An Acto-Myosin II Constricting Ring Initiates the Fission of Activity-Dependent Bulk Endosomes in Neurosecretory Cells

Activity-dependent bulk endocytosis allows neurons to internalize large portions of the plasma membrane in response to stimulation. However, whether this critical type of compensatory endocytosis is unique to neurons or also occurs in other excitable cells is currently unknown. Here we used fluorescent 70 kDa dextran to demonstrate that secretagogue-induced bulk endocytosis also occurs in bovine chromaffin cells. The relatively large size of the bulk endosomes found in this model allowed us to investigate how the neck of the budding endosomes constricts to allow efficient recruitment of the fission machinery. Using time-lapse imaging of Lifeact–GFP-transfected chromaffin cells in combination with fluorescent 70 kDa dextran, we detected acto-myosin II rings surrounding dextran-positive budding endosomes. Importantly, these rings were transient and contracted before disappearing, suggesting that they might be involved in restricting the size of the budding endosome neck. Based on the complete recovery of dextran fluorescence after photobleaching, we demonstrated that the actin ring-associated budding endosomes were still connected with the extracellular fluid. In contrast, no such recovery was observed following the constriction and disappearance of the actin rings, suggesting that these structures were pinched-off endosomes. Finally, we showed that the rings were initiated by a circular array of phosphatidylinositol(4,5)bisphosphate microdomains, and that their constriction was sensitive to both myosin II and dynamin inhibition. The acto-myosin II rings therefore play a key role in constricting the neck of budding bulk endosomes before dynamin-dependent fission from the plasma membrane of neurosecretory cells.

Hyperexcitability of Rat Thalamocortical Networks after Exposure to General Anesthesia during Brain Development

Prevailing literature supports the idea that common general anesthetics (GAs) cause long-term cognitive changes and neurodegeneration in the developing mammalian brain, especially in the thalamus. However, the possible role of GAs in modifying ion channels that control neuronal excitability has not been taken into consideration. Here we show that rats exposed to GAs at postnatal day 7 display a lasting reduction in inhibitory synaptic transmission, an increase in excitatory synaptic transmission, and concomitant increase in the amplitude of T-type calcium currents (T-currents) in neurons of the nucleus reticularis thalami (nRT). Collectively, this plasticity of ionic currents leads to increased action potential firing in vitro and increased strength of pharmacologically induced spike and wave discharges in vivo. Selective blockade of T-currents reversed neuronal hyperexcitability in vitro and in vivo. We conclude that drugs that regulate thalamic excitability may improve the safety of GAs used during early brain development.

Mechanism of Neuromuscular Dysfunction in Krabbe Disease

The atrophy of skeletal muscles in patients with Krabbe disease is a major debilitating manifestation that worsens their quality of life and limits the clinical efficacy of current therapies. The pathogenic mechanism triggering muscle wasting is unknown. This study examined structural, functional, and metabolic changes conducive to muscle degeneration in Krabbe disease using the murine (twitcher mouse) and canine [globoid cell leukodystrophy (GLD) dog] models. Muscle degeneration, denervation, neuromuscular [neuromuscular junction (NMJ)] abnormalities, and axonal death were investigated using the reporter transgenic twitcher–Thy1.1–yellow fluorescent protein mouse. We found that mutant muscles had significant numbers of smaller-sized muscle fibers, without signs of regeneration. Muscle growth was slow and weak in twitcher mice, with decreased maximum force. The NMJ had significant levels of activated caspase-3 but limited denervation. Mutant NMJ showed reduced surface areas and lower volumes of presynaptic terminals, with depressed nerve control, increased miniature endplate potential (MEPP) amplitude, decreased MEPP frequency, and increased rise and decay rate constants. Twitcher and GLD dog muscles had significant capacity to store psychosine, the neurotoxin that accumulates in Krabbe disease. Mechanistically, muscle defects involved the inactivation of the Akt pathway and activation of the proteasome pathway. Our work indicates that muscular dysfunction in Krabbe disease is compounded by a pathogenic mechanism involving at least the failure of NMJ function, activation of proteosome degradation, and a reduction of the Akt pathway. Akt, which is key for muscle function, may constitute a novel target to complement in therapies for Krabbe disease.

The Role of Telomerase Protein TERT in Alzheimer's Disease and in Tau-Related Pathology In Vitro

The telomerase reverse transcriptase protein TERT has recently been demonstrated to have a variety of functions both in vitro and in vivo, which are distinct from its canonical role in telomere extension. In different cellular systems, TERT protein has been shown to be protective through its interaction with mitochondria. TERT has previously been found in rodent neurons, and we hypothesize that it might have a protective function in adult human brain. Here, we investigated the expression of TERT at different stages of Alzheimer's disease pathology (Braak Stages I-VI) in situ and the ability of TERT to protect against oxidative damage in an in vitro model of tau pathology. Our data reveal that TERT is expressed in vitro in mouse neurons and microglia, and in vivo in the cytoplasm of mature human hippocampal neurons and activated microglia, but is absent from astrocytes. Intriguingly, hippocampal neurons expressing TERT did not contain hyperphosphorylated tau. Vice versa, neurons that expressed high levels of pathological tau did not appear to express TERT protein. TERT protein colocalized with mitochondria in the hippocampus of Alzheimer's disease brains (Braak Stage VI), as well as in cultured neurons under conditions of oxidative stress. Our in vitro data suggest that the absence of TERT increases ROS generation and oxidative damage in neurons induced by pathological tau. Together, our findings suggest that TERT protein persists in neurons of the adult human brain, where it may have a protective role against tau pathology.

Bax Regulates Neuronal Ca2+ Homeostasis

Excessive Ca²⁺ entry during glutamate receptor overactivation ("excitotoxicity") induces acute or delayed neuronal death. We report here that deficiency in bax exerted broad neuroprotection against excitotoxic injury and oxygen/glucose deprivation in mouse neocortical neuron cultures and reduced infarct size, necrotic injury, and cerebral edema formation after middle cerebral artery occlusion in mice. Neuronal Ca²⁺ and mitochondrial membrane potential (_m) analysis during excitotoxic injury revealed that bax-deficient neurons showed significantly reduced Ca²⁺ transients during the NMDA excitation period and did not exhibit the deregulation of _m that was observed in their wild-type (WT) counterparts. Reintroduction of bax or a bax mutant incapable of proapoptotic oligomerization equally restored neuronal Ca²⁺ dynamics during NMDA excitation, suggesting that Bax controlled Ca²⁺ signaling independently of its role in apoptosis execution. Quantitative confocal imaging of intracellular ATP or mitochondrial Ca²⁺ levels using FRET-based sensors indicated that the effects of bax deficiency on Ca²⁺ handling were not due to enhanced cellular bioenergetics or increased Ca²⁺ uptake into mitochondria. We also observed that mitochondria isolated from WT or bax-deficient cells similarly underwent Ca²⁺-induced permeability transition. However, when Ca²⁺ uptake into the sarco/endoplasmic reticulum was blocked with the Ca²⁺-ATPase inhibitor thapsigargin, bax-deficient neurons showed strongly elevated cytosolic Ca²⁺ levels during NMDA excitation, suggesting that the ability of Bax to support dynamic ER Ca²⁺ handling is critical for cell death signaling during periods of neuronal overexcitation.

Neural Cell Adhesion Molecule 2 Promotes the Formation of Filopodia and Neurite Branching by Inducing Submembrane Increases in Ca2+ Levels

Changes in expression of the neural cell adhesion molecule 2 (NCAM2) have been proposed to contribute to neurodevelopmental disorders in humans. The role of NCAM2 in neuronal differentiation remains, however, poorly understood. Using genetically encoded Ca²⁺ reporters, we show that clustering of NCAM2 at the cell surface of mouse cortical neurons induces submembrane [Ca²⁺] spikes, which depend on the L-type voltage-dependent Ca²⁺ channels (VDCCs) and require activation of the protein tyrosine kinase c-Src. We also demonstrate that clustering of NCAM2 induces L-type VDCC- and c-Src-dependent activation of CaMKII. NCAM2-dependent submembrane [Ca²⁺] spikes colocalize with the bases of filopodia. NCAM2 activation increases the density of filopodia along neurites and neurite branching and outgrowth in an L-type VDCC-, c-Src-, and CaMKII-dependent manner. Our results therefore indicate that NCAM2 promotes the formation of filopodia and neurite branching by inducing Ca²⁺ influx and CaMKII activation. Changes in NCAM2 expression in Down syndrome and autistic patients may therefore contribute to abnormal neurite branching observed in these disorders.

Visual Landmark Information Gains Control of the Head Direction Signal at the Lateral Mammillary Nuclei

The neural representation of directional heading is conveyed by head direction (HD) cells located in an ascending circuit that includes projections from the lateral mammillary nuclei (LMN) to the anterodorsal thalamus (ADN) to the postsubiculum (PoS). The PoS provides return projections to LMN and ADN and is responsible for the landmark control of HD cells in ADN. However, the functional role of the PoS projection to LMN has not been tested. The present study recorded HD cells from LMN after bilateral PoS lesions to determine whether the PoS provides landmark control to LMN HD cells. After the lesion and implantation of electrodes, HD cell activity was recorded while rats navigated within a cylindrical arena containing a single visual landmark or while they navigated between familiar and novel arenas of a dual-chamber apparatus. PoS lesions disrupted the landmark control of HD cells and also disrupted the stability of the preferred firing direction of the cells in darkness. Furthermore, PoS lesions impaired the stable HD cell representation maintained by path integration mechanisms when the rat walked between familiar and novel arenas. These results suggest that visual information first gains control of the HD cell signal in the LMN, presumably via the direct PoS -> LMN projection. This visual landmark information then controls HD cells throughout the HD cell circuit.

Left Dorsal Speech Stream Components and Their Contribution to Phonological Processing

Models propose an auditory-motor mapping via a left-hemispheric dorsal speech-processing stream, yet its detailed contributions to speech perception and production are unclear. Using fMRI-navigated repetitive transcranial magnetic stimulation (rTMS), we virtually lesioned left dorsal stream components in healthy human subjects and probed the consequences on speech-related facilitation of articulatory motor cortex (M1) excitability, as indexed by increases in motor-evoked potential (MEP) amplitude of a lip muscle, and on speech processing performance in phonological tests. Speech-related MEP facilitation was disrupted by rTMS of the posterior superior temporal sulcus (pSTS), the sylvian parieto-temporal region (SPT), and by double-knock-out but not individual lesioning of pars opercularis of the inferior frontal gyrus (pIFG) and the dorsal premotor cortex (dPMC), and not by rTMS of the ventral speech-processing stream or an occipital control site. RTMS of the dorsal stream but not of the ventral stream or the occipital control site caused deficits specifically in the processing of fast transients of the acoustic speech signal. Performance of syllable and pseudoword repetition correlated with speech-related MEP facilitation, and this relation was abolished with rTMS of pSTS, SPT, and pIFG. Findings provide direct evidence that auditory-motor mapping in the left dorsal stream causes reliable and specific speech-related MEP facilitation in left articulatory M1. The left dorsal stream targets the articulatory M1 through pSTS and SPT constituting essential posterior input regions and parallel via frontal pathways through pIFG and dPMC. Finally, engagement of the left dorsal stream is necessary for processing of fast transients in the auditory signal.

Spontaneous Activity Does Not Predict Morphological Type in Cerebellar Interneurons

The effort to determine morphological and anatomically defined neuronal characteristics from extracellularly recorded physiological signatures has been attempted with varying success in different brain areas. Recent studies have attempted such classification of cerebellar interneurons (CINs) based on statistical measures of spontaneous activity. Previously, such efforts in different brain areas have used supervised clustering methods based on standard parameterizations of spontaneous interspike interval (ISI) histograms. We worried that this might bias researchers toward positive identification results and decided to take a different approach. We recorded CINs from anesthetized cats. We used unsupervised clustering methods applied to a nonparametric representation of the ISI histograms to identify groups of CINs with similar spontaneous activity and then asked how these groups map onto different cell types. Our approach was a fuzzy C-means clustering algorithm applied to the Kullbach–Leibler distances between ISI histograms. We found that there is, in fact, a natural clustering of the spontaneous activity of CINs into six groups but that there was no relationship between this clustering and the standard morphologically defined cell types. These results proved robust when generalization was tested to completely new datasets, including datasets recorded under different anesthesia conditions and in different laboratories and different species (rats). Our results suggest the importance of an unsupervised approach in categorizing neurons according to their extracellular activity. Indeed, a reexamination of such categorization efforts throughout the brain may be necessary. One important open question is that of functional differences of our six spontaneously defined clusters during actual behavior.

Trade-Off between Information Format and Capacity in the Olfactory System

As information about the sensory environment passes between layers within the nervous system, the format of the information often changes. To examine how information format affects the capacity of neurons to represent stimuli, we measured the rate of information transmission in olfactory neurons in intact, awake locusts (Schistocerca americana) while pharmacologically manipulating patterns of correlated neuronal activity. Blocking the periodic inhibition underlying odor-elicited neural oscillatory synchronization increased information transmission rates. This suggests oscillatory synchrony, which serves other information processing roles, comes at a cost to the speed with which neurons can transmit information. Our results provide an example of a trade-off between benefits and costs in neural information processing.

Propagating Waves Can Explain Irregular Neural Dynamics

Cortical neurons in vivo fire quite irregularly. Previous studies about the origin of such irregular neural dynamics have given rise to two major models: a balanced excitation and inhibition model, and a model of highly synchronized synaptic inputs. To elucidate the network mechanisms underlying synchronized synaptic inputs and account for irregular neural dynamics, we investigate a spatially extended, conductance-based spiking neural network model. We show that propagating wave patterns with complex dynamics emerge from the network model. These waves sweep past neurons, to which they provide highly synchronized synaptic inputs. On the other hand, these patterns only emerge from the network with balanced excitation and inhibition; our model therefore reconciles the two major models of irregular neural dynamics. We further demonstrate that the collective dynamics of propagating wave patterns provides a mechanistic explanation for a range of irregular neural dynamics, including the variability of spike timing, slow firing rate fluctuations, and correlated membrane potential fluctuations. In addition, in our model, the distributions of synaptic conductance and membrane potential are non-Gaussian, consistent with recent experimental data obtained using whole-cell recordings. Our work therefore relates the propagating waves that have been widely observed in the brain to irregular neural dynamics. These results demonstrate that neural firing activity, although appearing highly disordered at the single-neuron level, can form dynamical coherent structures, such as propagating waves at the population level.

Alpha and Beta Band Event-Related Desynchronization Reflects Kinematic Regularities

The short-lasting attenuation of brain oscillations is termed event-related desynchronization (ERD). It is frequently found in the alpha and beta bands in humans during generation, observation, and imagery of movement and is considered to reflect cortical motor activity and action-perception coupling. The shared information driving ERD in all these motor-related behaviors is unknown. We investigated whether particular laws governing production and perception of curved movement may account for the attenuation of alpha and beta rhythms. Human movement appears to be governed by relatively few kinematic laws of motion. One dominant law in biological motion kinematics is the 2/3 power law (PL), which imposes a strong dependency of movement speed on curvature and is prominent in action-perception coupling. Here we directly examined whether the 2/3 PL elicits ERD during motion observation by characterizing the spatiotemporal signature of ERD. ERDs were measured while human subjects observed a cloud of dots moving along elliptical trajectories either complying with or violating the 2/3 PL. We found that ERD within both frequency bands was consistently stronger, arose faster, and was more widespread while observing motion obeying the 2/3 PL. An activity pattern showing clear 2/3 PL preference and lying within the alpha band was observed exclusively above central motor areas, whereas 2/3 PL preference in the beta band was observed in additional prefrontal–central cortical sites. Our findings reveal that compliance with the 2/3 PL is sufficient to elicit a selective ERD response in the human brain.

Elucidating the Role of AII Amacrine Cells in Glutamatergic Retinal Waves

Spontaneous retinal activity mediated by glutamatergic neurotransmission—so-called "Stage 3" retinal waves—drives anti-correlated spiking in ON and OFF RGCs during the second week of postnatal development of the mouse. In the mature retina, the activity of a retinal interneuron called the AII amacrine cell is responsible for anti-correlated spiking in ON and OFF α-RGCs. In mature AIIs, membrane hyperpolarization elicits bursting behavior. Here, we postulated that bursting in AIIs underlies the initiation of glutamatergic retinal waves. We tested this hypothesis by using two-photon calcium imaging of spontaneous activity in populations of retinal neurons and by making whole-cell recordings from individual AIIs and α-RGCs in in vitro preparations of mouse retina. We found that AIIs participated in retinal waves, and that their activity was correlated with that of ON α-RGCs and anti-correlated with that of OFF α-RGCs. Though immature AIIs lacked the complement of membrane conductances necessary to generate bursting, pharmacological activation of the M-current, a conductance that modulates bursting in mature AIIs, blocked retinal wave generation. Interestingly, blockade of the pacemaker conductance I_h, a conductance absent in AIIs but present in both ON and OFF cone bipolar cells, caused a dramatic loss of spatial coherence of spontaneous activity. We conclude that during glutamatergic waves, AIIs act to coordinate and propagate activity generated by BCs rather than to initiate spontaneous activity.

Neural Correlates of Object-Associated Choice Behavior in the Perirhinal Cortex of Rats

The perirhinal cortex (PRC) is reportedly important for object recognition memory, with supporting physiological evidence obtained largely from primate studies. Whether neurons in the rodent PRC also exhibit similar physiological correlates of object recognition, however, remains to be determined. We recorded single units from the PRC in a PRC-dependent, object-cued spatial choice task in which, when cued by an object image, the rat chose the associated spatial target from two identical discs appearing on a touchscreen monitor. The firing rates of PRC neurons were significantly modulated by critical events in the task, such as object sampling and choice response. Neuronal firing in the PRC was correlated primarily with the conjunctive relationships between an object and its associated choice response, although some neurons also responded to the choice response alone. However, we rarely observed a PRC neuron that represented a specific object exclusively regardless of spatial response in rats, although the neurons were influenced by the perceptual ambiguity of the object at the population level. Some PRC neurons fired maximally after a choice response, and this post-choice feedback signal significantly enhanced the neuronal specificity for the choice response in the subsequent trial. Our findings suggest that neurons in the rat PRC may not participate exclusively in object recognition memory but that their activity may be more dynamically modulated in conjunction with other variables, such as choice response and its outcomes.

Plasticity during Motherhood: Changes in Excitatory and Inhibitory Layer 2/3 Neurons in Auditory Cortex

Maternal behavior can be triggered by auditory and olfactory cues originating from the newborn. Here we report how the transition to motherhood affects excitatory and inhibitory neurons in layer 2/3 (L2/3) of the mouse primary auditory cortex. We used in vivo two-photon targeted cell-attached recording to compare the response properties of parvalbumin-expressing neurons (PVNs) and pyramidal glutamatergic neurons (PyrNs). The transition to motherhood shifts the average best frequency of PVNs to higher frequency by a full octave, with no significant effect on average best frequency of PyrNs. The presence of pup odors significantly reduced the spontaneous and evoked activity of PVN. This reduction of feedforward inhibition coincides with a complimentary increase in spontaneous and evoked activity of PyrNs. The selective shift of PVN frequency tuning should render pup odor-induced disinhibition more effective for high-frequency stimuli, such as ultrasonic vocalizations. Indeed, pup odors increased neuronal responses of PyrNs to pup ultrasonic vocalizations. We conclude that plasticity in the mothers is mediated, at least in part, via modulation of the feedforward inhibition circuitry in the auditory cortex.

Daily Marijuana Use Is Not Associated with Brain Morphometric Measures in Adolescents or Adults

Recent research has suggested that marijuana use is associated with volumetric and shape differences in subcortical structures, including the nucleus accumbens and amygdala, in a dose-dependent fashion. Replication of such results in well controlled studies is essential to clarify the effects of marijuana. To that end, this retrospective study examined brain morphology in a sample of adult daily marijuana users (n = 29) versus nonusers (n = 29) and a sample of adolescent daily users (n = 50) versus nonusers (n = 50). Groups were matched on a critical confounding variable, alcohol use, to a far greater degree than in previously published studies. We acquired high-resolution MRI scans, and investigated group differences in gray matter using voxel-based morphometry, surface-based morphometry, and shape analysis in structures suggested to be associated with marijuana use, as follows: the nucleus accumbens, amygdala, hippocampus, and cerebellum. No statistically significant differences were found between daily users and nonusers on volume or shape in the regions of interest. Effect sizes suggest that the failure to find differences was not due to a lack of statistical power, but rather was due to the lack of even a modest effect. In sum, the results indicate that, when carefully controlling for alcohol use, gender, age, and other variables, there is no association between marijuana use and standard volumetric or shape measurements of subcortical structures.

Lymphocytes from Chronically Stressed Mice Confer Antidepressant-Like Effects to Naive Mice

We examined whether cells of the adaptive immune system retain the memory of psychosocial stress and thereby alter mood states and CNS function in the host. Lymphocytes from mice undergoing chronic social defeat stress or from unstressed control mice were isolated and adoptively transferred into naive lymphopenic Rag2^–/– mice. Changes in affective behavior, hippocampal cell proliferation, microglial activation states, and blood cytokine levels were examined in reconstituted stress-naive mice. The mice receiving lymphocytes from defeated donors showed less anxiety, more social behavior, and increased hippocampal cell proliferation compared with those receiving no cells or cells from unstressed donors. Mice receiving stressed immune cells had reduced pro-inflammatory cytokine levels in the blood relative to the other groups, an effect opposite to the elevated donor pro-inflammatory cytokine profile. Furthermore, mice receiving stressed immune cells had microglia skewed toward an anti-inflammatory, neuroprotective M2-like phenotype, an effect opposite the stressed donors' M1-like pro-inflammatory profile. However, stress had no effect on lymphocyte surface marker profiles in both donor and recipient mice. The data suggest that chronic stress-induced changes in the adaptive immune system, contrary to conferring anxiety and depressive behavior, protect against the deleterious effects of stress. Improvement in affective behavior is potentially mediated by reduced peripheral pro-inflammatory cytokine load, protective microglial activity, and increased hippocampal cell proliferation. The data identify the peripheral adaptive immune system as putatively involved in the mechanisms underlying stress resilience and a potential basis for developing novel rapid-acting antidepressant therapies.

Functional Consequences of Neurite Orientation Dispersion and Density in Humans across the Adult Lifespan

As humans age, a characteristic pattern of widespread neocortical dendritic disruption coupled with compensatory effects in hippocampus and other subcortical structures is shown in postmortem investigations. It is now possible to address age-related effects on gray matter (GM) neuritic organization and density in humans using multishell diffusion-weighted MRI and the neurite-orientation dispersion and density imaging (NODDI) model. In 45 healthy individuals across the adult lifespan (21–84 years), we used a multishell diffusion imaging and the NODDI model to assess the intraneurite volume fraction and neurite orientation-dispersion index (ODI) in GM tissues. We also determined the functional correlates of variations in GM microstructure by obtaining resting-state fMRI and behavioral data. We found a significant age-related deficit in neocortical ODI (most prominently in frontoparietal regions), whereas increased ODI was observed in hippocampus and cerebellum with advancing age. Neocortical ODI outperformed cortical thickness and white matter fractional anisotropy for the prediction of chronological age in the same individuals. Higher GM ODI sampled from resting-state networks with known age-related susceptibility (default mode and visual association networks) was associated with increased functional connectivity of these networks, whereas the task-positive networks tended to show no association or even decreased connectivity. Frontal pole ODI mediated the negative relationship of age with executive function, whereas hippocampal ODI mediated the positive relationship of age with executive function. Our in vivo findings align very closely with the postmortem data and provide evidence for vulnerability and compensatory neural mechanisms of aging in GM microstructure that have functional and cognitive impact in vivo.

Designer Receptors Enhance Memory in a Mouse Model of Down Syndrome

Dissociable Roles for the Basolateral Amygdala and Orbitofrontal Cortex in Decision-Making under Risk of Punishment

Several neuropsychiatric disorders are associated with abnormal decision-making involving risk of punishment, but the neural basis of this association remains poorly understood. Altered activity in brain systems including the basolateral amygdala (BLA) and orbitofrontal cortex (OFC) can accompany these same disorders, and these structures are implicated in some forms of decision-making. The current study investigated the role of the BLA and OFC in decision-making under risk of explicit punishment. Rats were trained in the risky decision-making task (RDT), in which they chose between two levers, one that delivered a small safe reward, and the other that delivered a large reward accompanied by varying risks of footshock punishment. Following training, they received sham or neurotoxic lesions of BLA or OFC, followed by RDT retesting. BLA lesions increased choice of the large risky reward (greater risk-taking) compared to both prelesion performance and sham controls. When reward magnitudes were equated, both BLA lesion and control groups shifted their choice to the safe (no shock) reward lever, indicating that the lesions did not impair punishment sensitivity. In contrast to BLA lesions, OFC lesions significantly decreased risk-taking compared with sham controls, but did not impair discrimination between different reward magnitudes or alter baseline levels of anxiety. Finally, neither lesion significantly affected food-motivated lever pressing under various fixed ratio schedules, indicating that lesion-induced alterations in risk-taking were not secondary to changes in appetitive motivation. Together, these findings indicate distinct roles for the BLA and OFC in decision-making under risk of explicit punishment.

Sustained Maintenance of Somatotopic Information in Brain Regions Recruited by Tactile Working Memory

To adaptively guide ongoing behavior, representations in working memory (WM) often have to be modified in line with changing task demands. We used event-related potentials (ERPs) to demonstrate that tactile WM representations are stored in modality-specific cortical regions, that the goal-directed modulation of these representations is mediated through hemispheric-specific activation of somatosensory areas, and that the rehearsal of somatotopic coordinates in memory is accomplished by modality-specific spatial attention mechanisms. Participants encoded two tactile sample stimuli presented simultaneously to the left and right hands, before visual retro-cues indicated which of these stimuli had to be retained to be matched with a subsequent test stimulus on the same hand. Retro-cues triggered a sustained tactile contralateral delay activity component with a scalp topography over somatosensory cortex contralateral to the cued hand. Early somatosensory ERP components to task-irrelevant probe stimuli (that were presented after the retro-cues) and to subsequent test stimuli were enhanced when these stimuli appeared at the currently memorized location relative to other locations on the cued hand, demonstrating that a precise focus of spatial attention was established during the selective maintenance of tactile events in WM. These effects were observed regardless of whether participants performed the matching task with uncrossed or crossed hands, indicating that WM representations in this task were based on somatotopic rather than allocentric spatial coordinates. In conclusion, spatial rehearsal in tactile WM operates within somatotopically organized sensory brain areas that have been recruited for information storage.

Behavioral and Circuit Basis of Sucrose Rejection by Drosophila Females in a Simple Decision-Making Task

Drosophila melanogaster egg-laying site selection offers a genetic model to study a simple form of value-based decision. We have previously shown that Drosophila females consistently reject a sucrose-containing substrate and choose a plain (sucrose-free) substrate for egg laying in our sucrose versus plain decision assay. However, either substrate is accepted when it is the sole option. Here we describe the neural mechanism that underlies females' sucrose rejection in our sucrose versus plain assay. First, we demonstrate that females explored the sucrose substrate frequently before most egg-laying events, suggesting that they actively suppress laying eggs on the sucrose substrate as opposed to avoiding visits to it. Second, we show that activating a specific subset of DA neurons triggered a preference for laying eggs on the sucrose substrate over the plain one, suggesting that activating these DA neurons can increase the value of the sucrose substrate for egg laying. Third, we demonstrate that neither ablating nor inhibiting the mushroom body (MB), a known Drosophila learning and decision center, affected females' egg-laying preferences in our sucrose versus plain assay, suggesting that MB does not mediate this specific decision-making task. We propose that the value of a sucrose substrate— as an egg-laying option—can be adjusted by the activities of a specific DA circuit. Once the sucrose substrate is determined to be the lesser valued option, females execute their decision to reject this inferior substrate not by stopping their visits to it, but by actively suppressing their egg-laying motor program during their visits.

The Effects of an APOE Promoter Polymorphism on Human Cortical Morphology during Nondemented Aging

Apolipoprotein E (APOE) is the best-known susceptibility gene for AD. It has been well demonstrated that the 4 allele of the APOE gene can affect brain structure/function in nondemented individuals; however, other polymorphisms in the APOE gene have been largely overlooked when assessing the effects of APOE on the neural system. Rs405509 is a newly recognized AD-related polymorphism located in the APOE promoter region that can regulate the transcriptional activity of the APOE gene. To date, it remains unknown whether and how this APOE promoter polymorphism affects the human brain in aging. Here, for the first time, we investigate the effects of the rs405509 genotype (T/T vs G-allele) on human cortical morphology using a large cohort of nondemented elderly subjects (120 subjects in total; aged 52– 81 years). High-resolution structural MRI was performed; cortical thickness and surface area were analyzed separately. Intriguingly, nondemented carriers of the rs405509 T/T genotype showed an accelerated age-related reduction of thickness in the left parahippocampal gyrus compared with the G-allele carriers. Furthermore, the cortical thickness covariance between the left parahippocampal gyrus and left medial cortex, including the left medial superior frontal gyrus, supplementary motor area, and paracentral lobule, was modulated by the interaction of the rs405509 genotype and age. These novel findings suggest an important role for the APOE promoter polymorphism in the human brain and also provide valuable insights into how the rs405509 genotype shapes the neural system to modulate the risk of developing AD.

Neural Alpha Dynamics in Younger and Older Listeners Reflect Acoustic Challenges and Predictive Benefits

Speech comprehension in multitalker situations is a notorious real-life challenge, particularly for older listeners. Younger listeners exploit stimulus-inherent acoustic detail, but are they also actively predicting upcoming information? And further, how do older listeners deal with acoustic and predictive information? To understand the neural dynamics of listening difficulties and according listening strategies, we contrasted neural responses in the alpha-band (~10 Hz) in younger (20–30 years, n = 18) and healthy older (60–70 years, n = 20) participants under changing task demands in a two-talker paradigm. Electroencephalograms were recorded while humans listened to two spoken digits against a distracting talker and decided whether the second digit was smaller or larger. Acoustic detail (temporal fine structure) and predictiveness (the degree to which the first digit predicted the second) varied orthogonally. Alpha power at widespread scalp sites decreased with increasing acoustic detail (during target digit presentation) but also with increasing predictiveness (in-between target digits). For older compared with younger listeners, acoustic detail had a stronger impact on task performance and alpha power modulation. This suggests that alpha dynamics plays an important role in the changes in listening behavior that occur with age. Last, alpha power variations resulting from stimulus manipulations (of acoustic detail and predictiveness) as well as task-independent overall alpha power were related to subjective listening effort. The present data show that alpha dynamics is a promising neural marker of individual difficulties as well as age-related changes in sensation, perception, and comprehension in complex communication situations.

Seeing Is Not Feeling: Posterior Parietal But Not Somatosensory Cortex Engagement During Touch Observation

Observing touch has been reported to elicit activation in human primary and secondary somatosensory cortices and is suggested to underlie our ability to interpret other's behavior and potentially empathy. However, despite these reports, there are a large number of inconsistencies in terms of the precise topography of activation, the extent of hemispheric lateralization, and what aspects of the stimulus are necessary to drive responses. To address these issues, we investigated the localization and functional properties of regions responsive to observed touch in a large group of participants (n = 40). Surprisingly, even with a lenient contrast of hand brushing versus brushing alone, we did not find any selective activation for observed touch in the hand regions of somatosensory cortex but rather in superior and inferior portions of neighboring posterior parietal cortex, predominantly in the left hemisphere. These regions in the posterior parietal cortex required the presence of both brush and hand to elicit strong responses and showed some selectivity for the form of the object or agent of touch. Furthermore, the inferior parietal region showed nonspecific tactile and motor responses, suggesting some similarity to area PFG in the monkey. Collectively, our findings challenge the automatic engagement of somatosensory cortex when observing touch, suggest mislocalization in previous studies, and instead highlight the role of posterior parietal cortex.

Action and Perception Are Temporally Coupled by a Common Mechanism That Leads to a Timing Misperception

We move our eyes to explore the world, but visual areas determining where to look next (action) are different from those determining what we are seeing (perception). Whether, or how, action and perception are temporally coordinated is not known. The preparation time course of an action (e.g., a saccade) has been widely studied with the gap/overlap paradigm with temporal asynchronies (TA) between peripheral target onset and fixation point offset (gap, synchronous, or overlap). However, whether the subjects perceive the gap or overlap, and when they perceive it, has not been studied. We adapted the gap/overlap paradigm to study the temporal coupling of action and perception. Human subjects made saccades to targets with different TAs with respect to fixation point offset and reported whether they perceived the stimuli as separated by a gap or overlapped in time. Both saccadic and perceptual report reaction times changed in the same way as a function of TA. The TA dependencies of the time change for action and perception were very similar, suggesting a common neural substrate. Unexpectedly, in the perceptual task, subjects misperceived lights overlapping by less than ~100 ms as separated in time (overlap seen as gap). We present an attention-perception model with a map of prominence in the superior colliculus that modulates the stimulus signal's effectiveness in the action and perception pathways. This common source of modulation determines how competition between stimuli is resolved, causes the TA dependence of action and perception to be the same, and causes the misperception.

Direct Physiologic Evidence of a Heteromodal Convergence Region for Proper Naming in Human Left Anterior Temporal Lobe

Retrieving the names of friends, loved ones, and famous people is a fundamental human ability. This ability depends on the left anterior temporal lobe (ATL), where lesions can be associated with impaired naming of people regardless of modality (e.g., picture or voice). This finding has led to the idea that the left ATL is a modality-independent convergence region for proper naming. Hypotheses for how proper-name dispositions are organized within the left ATL include both a single modality-independent (heteromodal) convergence region and spatially discrete modality-dependent (unimodal) regions. Here we show direct electrophysiologic evidence that the left ATL is heteromodal for proper-name retrieval. Using intracranial recordings placed directly on the surface of the left ATL in human subjects, we demonstrate nearly identical responses to picture and voice stimuli of famous U.S. politicians during a naming task. Our results demonstrate convergent and robust large-scale neurophysiologic responses to picture and voice naming in the human left ATL. This finding supports the idea of heteromodal (i.e., transmodal) dispositions for proper naming in the left ATL.

Neural Decoding Reveals Impaired Face Configural Processing in the Right Fusiform Face Area of Individuals with Developmental Prosopagnosia

Most of human daily social interactions rely on the ability to successfully recognize faces. Yet ~2% of the human population suffers from face blindness without any acquired brain damage [this is also known as developmental prosopagnosia (DP) or congenital prosopagnosia]). Despite the presence of severe behavioral face recognition deficits, surprisingly, a majority of DP individuals exhibit normal face selectivity in the right fusiform face area (FFA), a key brain region involved in face configural processing. This finding, together with evidence showing impairments downstream from the right FFA in DP individuals, has led some to argue that perhaps the right FFA is largely intact in DP individuals. Using fMRI multivoxel pattern analysis, here we report the discovery of a neural impairment in the right FFA of DP individuals that may play a critical role in mediating their face-processing deficits. In seven individuals with DP, we discovered that, despite the right FFA's preference for faces and it showing decoding for the different face parts, it exhibited impaired face configural decoding and did not contain distinct neural response patterns for the intact and the scrambled face configurations. This abnormality was not present throughout the ventral visual cortex, as normal neural decoding was found in an adjacent object-processing region. To our knowledge, this is the first direct neural evidence showing impaired face configural processing in the right FFA in individuals with DP. The discovery of this neural impairment provides a new clue to our understanding of the neural basis of DP.

Neural Correlates of Expected Risks and Returns in Risky Choice across Development

Adolescence is often described as a period of increased risk taking relative to both childhood and adulthood. This inflection in risky choice behavior has been attributed to a neurobiological imbalance between earlier developing motivational systems and later developing top-down control regions. Yet few studies have decomposed risky choice to investigate the underlying mechanisms or tracked their differential developmental trajectory. The current study uses a risk–return decomposition to more precisely assess the development of processes underlying risky choice and to link them more directly to specific neural mechanisms. This decomposition specifies the influence of changing risks (outcome variability) and changing returns (expected value) on the choices of children, adolescents, and adults in a dynamic risky choice task, the Columbia Card Task. Behaviorally, risk aversion increased across age groups, with adults uniformly risk averse and adolescents showing substantial individual differences in risk sensitivity, ranging from risk seeking to risk averse. Neurally, we observed an adolescent peak in risk-related activation in the anterior insula and dorsal medial PFC. Return sensitivity, on the other hand, increased monotonically across age groups and was associated with increased activation in the ventral medial PFC and posterior cingulate cortex with age. Our results implicate adolescence as a developmental phase of increased neural risk sensitivity. Importantly, this work shows that using a behaviorally validated decision-making framework allows a precise operationalization of key constructs underlying risky choice that inform the interpretation of results.

Dynamic Modulation of the Action Observation Network by Movement Familiarity

When watching another person's actions, a network of sensorimotor brain regions, collectively termed the action observation network (AON), is engaged. Previous research suggests that the AON is more responsive when watching familiar compared with unfamiliar actions. However, most research into AON function is premised on comparisons of AON engagement during different types of task using univariate, magnitude-based approaches. To better understand the relationship between action familiarity and AON engagement, here we examine how observed movement familiarity modulates AON activity in humans using dynamic causal modeling, a type of effective connectivity analysis. Twenty-one subjects underwent fMRI scanning while viewing whole-body dance movements that varied in terms of their familiarity. Participants' task was to either predict the next posture the dancer's body would assume or to respond to a non–action-related attentional control question. To assess individuals' familiarity with each movement, participants rated each video on a measure of visual familiarity after being scanned. Parametric analyses showed more activity in left middle temporal gyrus, inferior parietal lobule, and inferior frontal gyrus as videos were rated as increasingly familiar. These clusters of activity formed the regions of interest for dynamic causal modeling analyses, which revealed attenuation of effective connectivity bidirectionally between parietal and temporal AON nodes when participants observed videos they rated as increasingly familiar. As such, the findings provide partial support for a predictive coding model of the AON, as well as illuminate how action familiarity manipulations can be used to explore simulation-based accounts of action understanding.

Rescue of Impaired Long-Term Facilitation at Sensorimotor Synapses of Aplysia following siRNA Knockdown of CREB1

Memory impairment is often associated with disrupted regulation of gene induction. For example, deficits in cAMP response element-binding protein (CREB) binding protein (CBP; an essential cofactor for activation of transcription by CREB) impair long-term synaptic plasticity and memory. Previously, we showed that small interfering RNA (siRNA)-induced knockdown of CBP in individual sensory neurons significantly reduced levels of CBP and impaired 5-HT-induced long-term facilitation (LTF) in sensorimotor cocultures from Aplysia. Moreover, computational simulations of the biochemical cascades underlying LTF successfully predicted training protocols that restored LTF following CBP knockdown. We examined whether simulations could also predict a training protocol that restores LTF impaired by siRNA-induced knockdown of the transcription factor CREB1. Simulations based on a previously described model predicted rescue protocols that were specific to CREB1 knockdown. Empirical studies demonstrated that one of these rescue protocols partially restored impaired LTF. In addition, the effectiveness of the rescue protocol was enhanced by pretreatment with rolipram, a selective cAMP phosphodiesterase inhibitor. These results provide further evidence that computational methods can help rescue disruptions in signaling cascades underlying memory formation. Moreover, the study demonstrates that the effectiveness of computationally designed training protocols can be enhanced with complementary pharmacological approaches.

Frontal Eye Fields Control Attentional Modulation of Alpha and Gamma Oscillations in Contralateral Occipitoparietal Cortex

Covertly directing visuospatial attention produces a frequency-specific modulation of neuronal oscillations in occipital and parietal cortices: anticipatory alpha (8–12 Hz) power decreases contralateral and increases ipsilateral to attention, whereas stimulus-induced gamma (>40 Hz) power is boosted contralaterally and attenuated ipsilaterally. These modulations must be under top-down control; however, the control mechanisms are not yet fully understood. Here we investigated the causal contribution of the human frontal eye field (FEF) by combining repetitive transcranial magnetic stimulation (TMS) with subsequent magnetoencephalography. Following inhibitory theta burst stimulation to the left FEF, right FEF, or vertex, participants performed a visual discrimination task requiring covert attention to either visual hemifield. Both left and right FEF TMS caused marked attenuation of alpha modulation in the occipitoparietal cortex. Notably, alpha modulation was consistently reduced in the hemisphere contralateral to stimulation, leaving the ipsilateral hemisphere relatively unaffected. Additionally, right FEF TMS enhanced gamma modulation in left visual cortex. Behaviorally, TMS caused a relative slowing of response times to targets contralateral to stimulation during the early task period. Our results suggest that left and right FEF are causally involved in the attentional top-down control of anticipatory alpha power in the contralateral visual system, whereas a right-hemispheric dominance seems to exist for control of stimulus-induced gamma power. These findings contrast the assumption of primarily intrahemispheric connectivity between FEF and parietal cortex, emphasizing the relevance of interhemispheric interactions. The contralaterality of effects may result from a transient functional reorganization of the dorsal attention network after inhibition of either FEF.

Local Morphology Predicts Functional Organization of Experienced Value Signals in the Human Orbitofrontal Cortex

Experienced value representations within the human orbitofrontal cortex (OFC) are thought to be organized through an antero-posterior gradient corresponding to secondary versus primary rewards. Whether this gradient depends upon specific morphological features within this region, which displays considerable intersubject variability, remains unknown. To test the existence of such relationships, we performed a subject-by-subject analysis of fMRI data taking into account the local morphology of each individual. We tested 38 subjects engaged in a simple incentive delay task manipulating both monetary and visual erotic rewards, focusing on reward outcome (experienced value signal). The results showed reliable and dissociable primary (erotic) and secondary (monetary) experienced value signals at specific OFC sulci locations. More specifically, experienced value signal induced by monetary reward outcome was systematically located in the rostral portion of the medial orbital sulcus. Experienced value signal related to erotic reward outcome was located more posteriorly, that is, at the intersection between the caudal portion of the medial orbital sulcus and transverse orbital sulcus. Thus, the localizations of distinct experienced value signals can be predicted from the organization of the human orbitofrontal sulci. This study provides insights into the anatomo-functional parcellation of the anteroposterior OFC gradient observed for secondary versus primary rewards because there is a direct relationship between value signals at the time of reward outcome and unique OFC sulci locations.

Recollection-Related Increases in Functional Connectivity Predict Individual Differences in Memory Accuracy

Recollection involves retrieving specific contextual details about a prior event. Functional neuroimaging studies have identified several brain regions that are consistently more active during successful versus failed recollection—the "core recollection network." In the present study, we investigated whether these regions demonstrate recollection-related increases not only in activity but also in functional connectivity in healthy human adults. We used fMRI to compare time-series correlations during successful versus unsuccessful recollection in three separate experiments, each using a different operational definition of recollection. Across experiments, a broadly distributed set of regions consistently exhibited recollection-related increases in connectivity with different members of the core recollection network. Regions that demonstrated this effect included both recollection-sensitive regions and areas where activity did not vary as a function of recollection success. In addition, in all three experiments the magnitude of connectivity increases correlated across individuals with recollection accuracy in areas diffusely distributed throughout the brain. These findings suggest that enhanced functional interactions between distributed brain regions are a signature of successful recollection. In addition, these findings demonstrate that examining dynamic modulations in functional connectivity during episodic retrieval will likely provide valuable insight into neural mechanisms underlying individual differences in memory performance.

Creatine Supplementation Enhances Corticomotor Excitability and Cognitive Performance during Oxygen Deprivation

Impairment or interruption of oxygen supply compromises brain function and plays a role in neurological and neurodegenerative conditions. Creatine is a naturally occurring compound involved in the buffering, transport, and regulation of cellular energy, with the potential to replenish cellular adenosine triphosphate without oxygen. Creatine is also neuroprotective in vitro against anoxic/hypoxic damage. Dietary creatine supplementation has been associated with improved symptoms in neurological disorders defined by impaired neural energy provision. Here we investigate, for the first time in humans, the utility of creatine as a dietary supplement to protect against energetic insult. The aim of this study was to assess the influence of oral creatine supplementation on the neurophysiological and neuropsychological function of healthy young adults during acute oxygen deprivation. Fifteen healthy adults were supplemented with creatine and placebo treatments for 7 d, which increased brain creatine on average by 9.2%. A hypoxic gas mixture (10% oxygen) was administered for 90 min, causing global oxygen deficit and impairing a range of neuropsychological processes. Hypoxia-induced decrements in cognitive performance, specifically attentional capacity, were restored when participants were creatine supplemented, and corticomotor excitability increased. A neuromodulatory effect of creatine via increased energy availability is presumed to be a contributing factor of the restoration, perhaps by supporting the maintenance of appropriate neuronal membrane potentials. Dietary creatine monohydrate supplementation augments neural creatine, increases corticomotor excitability, and prevents the decline in attention that occurs during severe oxygen deficit. This is the first demonstration of creatine's utility as a neuroprotective supplement when cellular energy provision is compromised.

Morphometric and Histologic Substrates of Cingulate Integrity in Elders with Exceptional Memory Capacity

This human study is based on an established cohort of "SuperAgers," 80+-year-old individuals with episodic memory function at a level equal to, or better than, individuals 20–30 years younger. A preliminary investigation using structural brain imaging revealed a region of anterior cingulate cortex that was thicker in SuperAgers compared with healthy 50- to 65-year-olds. Here, we investigated the in vivo structural features of cingulate cortex in a larger sample of SuperAgers and conducted a histologic analysis of this region in postmortem specimens. A region-of-interest MRI structural analysis found cingulate cortex to be thinner in cognitively average 80+ year olds (n = 21) than in the healthy middle-aged group (n = 18). A region of the anterior cingulate cortex in the right hemisphere displayed greater thickness in SuperAgers (n = 31) compared with cognitively average 80+ year olds and also to the much younger healthy 50–60 year olds (p < 0.01). Postmortem investigations were conducted in the cingulate cortex in five SuperAgers, five cognitively average elderly individuals, and five individuals with amnestic mild cognitive impairment. Compared with other subject groups, SuperAgers showed a lower frequency of Alzheimer-type neurofibrillary tangles (p < 0.05). There were no differences in total neuronal size or count between subject groups. Interestingly, relative to total neuronal packing density, there was a higher density of von Economo neurons (p < 0.05), particularly in anterior cingulate regions of SuperAgers. These findings suggest that reduced vulnerability to the age-related emergence of Alzheimer pathology and higher von Economo neuron density in anterior cingulate cortex may represent biological correlates of high memory capacity in advanced old age.

Neural Mechanisms for Integrating Prior Knowledge and Likelihood in Value-Based Probabilistic Inference

In Bayesian decision theory, knowledge about the probabilities of possible outcomes is captured by a prior distribution and a likelihood function. The prior reflects past knowledge and the likelihood summarizes current sensory information. The two combined (integrated) form a posterior distribution that allows estimation of the probability of different possible outcomes. In this study, we investigated the neural mechanisms underlying Bayesian integration using a novel lottery decision task in which both prior knowledge and likelihood information about reward probability were systematically manipulated on a trial-by-trial basis. Consistent with Bayesian integration, as sample size increased, subjects tended to weigh likelihood information more compared with prior information. Using fMRI in humans, we found that the medial prefrontal cortex (mPFC) correlated with the mean of the posterior distribution, a statistic that reflects the integration of prior knowledge and likelihood of reward probability. Subsequent analysis revealed that both prior and likelihood information were represented in mPFC and that the neural representations of prior and likelihood in mPFC reflected changes in the behaviorally estimated weights assigned to these different sources of information in response to changes in the environment. Together, these results establish the role of mPFC in prior-likelihood integration and highlight its involvement in representing and integrating these distinct sources of information.

Listening to the Brainstem: Musicianship Enhances Intelligibility of Subcortical Representations for Speech

Auditory experiences including musicianship and bilingualism have been shown to enhance subcortical speech encoding operating below conscious awareness. Yet, the behavioral consequence of such enhanced subcortical auditory processing remains undetermined. Exploiting their remarkable fidelity, we examined the intelligibility of auditory playbacks (i.e., "sonifications") of brainstem potentials recorded in human listeners. We found naive listeners' behavioral classification of sonifications was faster and more categorical when evaluating brain responses recorded in individuals with extensive musical training versus those recorded in nonmusicians. These results reveal stronger behaviorally relevant speech cues in musicians' neural representations and demonstrate causal evidence that superior subcortical processing creates a more comprehensible speech signal (i.e., to naive listeners). We infer that neural sonifications of speech-evoked brainstem responses could be used in the early detection of speech–language impairments due to neurodegenerative disorders, or in objectively measuring individual differences in speech reception solely by listening to individuals' brain activity.

Plasticity of Intact Rubral Projections Mediates Spontaneous Recovery of Function after Corticospinal Tract Injury

Axons in the adult CNS fail to regenerate after injury, and therefore recovery from spinal cord injury (SCI) is limited. Although full recovery is rare, a modest degree of spontaneous recovery is observed consistently in a broad range of clinical and nonclinical situations. To define the mechanisms mediating spontaneous recovery of function after incomplete SCI, we created bilaterally complete medullary corticospinal tract lesions in adult mice, eliminating a crucial pathway for voluntary skilled movement. Anatomic and pharmacogenetic tools were used to identify the pathways driving spontaneous functional recovery in wild-type and plasticity-sensitized mice lacking Nogo receptor 1. We found that plasticity-sensitized mice recovered 50% of normal skilled locomotor function within 5 weeks of lesion. This significant, yet incomplete, spontaneous recovery was accompanied by extensive sprouting of intact rubrofugal and rubrospinal projections with the emergence of a de novo circuit between the red nucleus and the nucleus raphe magnus. Transient silencing of this rubro–raphe circuit in vivo via activation of the inhibitory DREADD (designer receptor exclusively activated by designer drugs) receptor hM4di abrogated spontaneous functional recovery. These data highlight the pivotal role of uninjured motor circuit plasticity in supporting functional recovery after trauma, and support a focus of experimental strategies on enhancing intact circuit rearrangement to promote functional recovery after SCI.

A Distinct Subtype of Dopaminergic Interneuron Displays Inverted Structural Plasticity at the Axon Initial Segment

The axon initial segment (AIS) is a specialized structure near the start of the axon that is a site of neuronal plasticity. Changes in activity levels in vitro and in vivo can produce structural AIS changes in excitatory cells that have been linked to alterations in excitability, but these effects have never been described in inhibitory interneurons. In the mammalian olfactory bulb (OB), dopaminergic interneurons are particularly plastic, undergoing constitutive turnover throughout life and regulating tyrosine hydroxylase expression in an activity-dependent manner. Here we used dissociated cultures of rat and mouse OB to show that a subset of bulbar dopaminergic neurons possess an AIS and that these AIS-positive cells are morphologically and functionally distinct from their AIS-negative counterparts. Under baseline conditions, OB dopaminergic AISs were short and located distally along the axon but, in response to chronic 24 h depolarization, lengthened and relocated proximally toward the soma. These activity-dependent changes were in the opposite direction to both those we saw in non-GABAergic OB neurons and those reported previously for excitatory cell types. Inverted AIS plasticity in OB dopaminergic cells was bidirectional, involved all major components of the structure, was dependent on the activity of L-type Ca_V1 calcium channels but not on the activity of the calcium-activated phosphatase calcineurin, and was opposed by the actions of cyclin-dependent kinase 5. Such distinct forms of AIS plasticity in inhibitory interneurons and excitatory projection neurons may allow considerable flexibility when neuronal networks must adapt to perturbations in their ongoing activity.

Opioid Receptor-Dependent Sex Differences in Synaptic Plasticity in the Hippocampal Mossy Fiber Pathway of the Adult Rat

Autocrine Boost of NMDAR Current in Hippocampal CA1 Pyramidal Neurons by a PMCA-Dependent, Perisynaptic, Extracellular pH Shift

The plasma membrane Ca²⁺-ATPase (PMCA) is found near postsynaptic NMDARs. This transporter is a Ca²⁺-H⁺ exchanger that raises cell surface pH. We tested whether the PMCA acts in an autocrine fashion to boost pH-sensitive, postsynaptic NMDAR currents. In mouse hippocampal slices, NMDAR EPSCs in a singly activated CA1 pyramidal neuron were reduced when buffering was augmented by exogenous carbonic anhydrase (XCAR). This effect was blocked by the enzyme inhibitor benzolamide and mimicked by the addition of HEPES buffer. Similar EPSC reduction occurred when PMCA activation was prevented by dialysis of BAPTA or the PMCA inhibitor carboxyeosin. Using HEPES, BAPTA, or carboxyeosin, the effect of XCAR was completely occluded. XCAR similarly curtailed NMDAR EPSCs of minimal amplitude, but had no effect on small AMPAR responses. These results indicate that a significant fraction of the postsynaptic NMDAR current is reliant on a perisynaptic extracellular alkaline shift generated by the PMCA.

The Spinal Muscular Atrophy with Pontocerebellar Hypoplasia Gene VRK1 Regulates Neuronal Migration through an Amyloid-{beta} Precursor Protein-Dependent Mechanism

Spinal muscular atrophy with pontocerebellar hypoplasia (SMA-PCH) is an infantile SMA variant with additional manifestations, particularly severe microcephaly. We previously identified a nonsense mutation in Vaccinia-related kinase 1 (VRK1), R358X, as a cause of SMA-PCH. VRK1-R358X is a rare founder mutation in Ashkenazi Jews, and additional mutations in patients of different origins have recently been identified. VRK1 is a nuclear serine/threonine protein kinase known to play multiple roles in cellular proliferation, cell cycle regulation, and carcinogenesis. However, VRK1 was not known to have neuronal functions before its identification as a gene mutated in SMA-PCH. Here we show that VRK1-R358X homozygosity results in lack of VRK1 protein, and demonstrate a role for VRK1 in neuronal migration and neuronal stem cell proliferation. Using shRNA in utero electroporation in mice, we show that Vrk1 knockdown significantly impairs cortical neuronal migration, and affects the cell cycle of neuronal progenitors. Expression of wild-type human VRK1 rescues both proliferation and migration phenotypes. However, kinase-dead human VRK1 rescues only the migration impairment, suggesting the role of VRK1 in neuronal migration is partly noncatalytic. Furthermore, we found that VRK1 deficiency in human and mouse leads to downregulation of amyloid-β precursor protein (APP), a known neuronal migration gene. APP overexpression rescues the phenotype caused by Vrk1 knockdown, suggesting that VRK1 affects neuronal migration through an APP-dependent mechanism.

NLP-12 Engages Different UNC-13 Proteins to Potentiate Tonic and Evoked Release

A neuropeptide (NLP-12) and its receptor (CKR-2) potentiate tonic and evoked ACh release at Caenorhabditis elegans neuromuscular junctions. Increased evoked release is mediated by a presynaptic pathway (egl-30 Gα_q and egl-8 PLCβ) that produces DAG, and by DAG binding to short and long UNC-13 proteins. Potentiation of tonic ACh release persists in mutants deficient for egl-30 Gα_q and egl-8 PLCβ and requires DAG binding to UNC-13L (but not UNC-13S). Thus, NLP-12 adjusts tonic and evoked release by distinct mechanisms.

Patterned, But Not Tonic, Optogenetic Stimulation in Motor Thalamus Improves Reaching in Acute Drug-Induced Parkinsonian Rats

High-frequency deep brain stimulation (DBS) in motor thalamus (Mthal) ameliorates tremor but not akinesia in Parkinson's disease. The aim of this study was to investigate whether there are effective methods of Mthal stimulation to treat akinesia. Glutamatergic Mthal neurons, transduced with channelrhodopsin-2 by injection of lentiviral vector (Lenti.CaMKII.hChR2(H134R).mCherry), were selectively stimulated with blue light (473 nm) via a chronically implanted fiber-optic probe. Rats performed a reach-to-grasp task in either acute drug-induced parkinsonian akinesia (0.03–0.07 mg/kg haloperidol, s.c.) or control (vehicle injection) conditions, and the number of reaches was recorded for 5 min before, during, and after stimulation. We compared the effect of DBS using complex physiological patterns previously recorded in the Mthal of a control rat during reaching or exploring behavior, with tonic DBS delivering the same number of stimuli per second (rate-control 6.2 or 1.8 Hz, respectively) and with stimulation patterns commonly used in other brain regions to treat neurological conditions (tonic 130 Hz, theta burst (TBS), and tonic 15 Hz rate-control for TBS). Control rats typically executed >150 reaches per 5 min, which was unaffected by any of the stimulation patterns. Acute parkinsonian rats executed <20 reaches, displaying marked akinesia, which was significantly improved by stimulating with the physiological reaching pattern or TBS (both p < 0.05), whereas the exploring and all tonic patterns failed to improve reaching. Data indicate that the Mthal may be an effective site to treat akinesia, but the pattern of stimulation is critical for improving reaching in parkinsonian rats.

Oligodendroglial Maturation Is Dependent on Intracellular Protein Shuttling

Multiple sclerosis is an autoimmune disease of the CNS resulting in degeneration of myelin sheaths and loss of oligodendrocytes, which means that protection and electrical insulation of axons and rapid signal propagation are impaired, leading to axonal damage and permanent disabilities. Partial replacement of lost oligodendrocytes and remyelination can occur as a result of activation and recruitment of resident oligodendroglial precursor cells. However, the overall remyelination capacity remains inefficient because precursor cells often fail to generate new oligodendrocytes. Increasing evidence points to the existence of several molecular inhibitors that act on these cells and interfere with their cellular maturation. The p57kip2 gene encodes one such potent inhibitor of oligodendroglial differentiation and this study sheds light on the underlying mode of action. We found that subcellular distribution of the p57kip2 protein changed during differentiation of rat, mouse, and human oligodendroglial cells both in vivo and in vitro. Nuclear export of p57kip2 was correlated with promoted myelin expression, higher morphological phenotypes, and enhanced myelination in vitro. In contrast, nuclear accumulation of p57kip2 resulted in blocked oligodendroglial differentiation. Experimental evidence suggests that the inhibitory role of p57kip2 depends on specific interactions with binding proteins such as LIMK-1, CDK2, Mash1, and Hes5 either by controlling their site of action or their activity. Because functional restoration in demyelinating diseases critically depends on the successful generation of oligodendroglial cells, a therapeutic need that is currently unmet, the regulatory mechanism described here might be of particular interest for identifying suitable drug targets and devising novel therapeutic approaches.

BDNF Stimulation of Protein Synthesis in Cortical Neurons Requires the MAP Kinase-Interacting Kinase MNK1

Although the MAP kinase-interacting kinases (MNKs) have been known for >15 years, their roles in the regulation of protein synthesis have remained obscure. Here, we explore the involvement of the MNKs in brain-derived neurotrophic factor (BDNF)-stimulated protein synthesis in cortical neurons from mice. Using a combination of pharmacological and genetic approaches, we show that BDNF-induced upregulation of protein synthesis requires MEK/ERK signaling and the downstream kinase, MNK1, which phosphorylates eukaryotic initiation factor (eIF) 4E. Translation initiation is mediated by the interaction of eIF4E with the m⁷GTP cap of mRNA and with eIF4G. The latter interaction is inhibited by the interactions of eIF4E with partner proteins, such as CYFIP1, which acts as a translational repressor. We find that BDNF induces the release of CYFIP1 from eIF4E, and that this depends on MNK1. Finally, using a novel combination of BONCAT and SILAC, we identify a subset of proteins whose synthesis is upregulated by BDNF signaling via MNK1 in neurons. Interestingly, this subset of MNK1-sensitive proteins is enriched for functions involved in neurotransmission and synaptic plasticity. Additionally, we find significant overlap between our subset of proteins whose synthesis is regulated by MNK1 and those encoded by known FMRP-binding mRNAs. Together, our data implicate MNK1 as a key component of BDNF-mediated translational regulation in neurons.

ATP Binding to Synaspsin IIa Regulates Usage and Clustering of Vesicles in Terminals of Hippocampal Neurons

Synaptic transmission is expensive in terms of its energy demands and was recently shown to decrease the ATP concentration within presynaptic terminals transiently, an observation that we confirm. We hypothesized that, in addition to being an energy source, ATP may modulate the synapsins directly. Synapsins are abundant neuronal proteins that associate with the surface of synaptic vesicles and possess a well defined ATP-binding site of undetermined function. To examine our hypothesis, we produced a mutation (K270Q) in synapsin IIa that prevents ATP binding and reintroduced the mutant into cultured mouse hippocampal neurons devoid of all synapsins. Remarkably, staining for synaptic vesicle markers was enhanced in these neurons compared with neurons expressing wild-type synapsin IIa, suggesting overly efficient clustering of vesicles. In contrast, the mutation completely disrupted the capability of synapsin IIa to slow synaptic depression during sustained 10 Hz stimulation, indicating that it interfered with synapsin-dependent vesicle recruitment. Finally, we found that the K270Q mutation attenuated the phosphorylation of synapsin IIa on a distant PKA/CaMKI consensus site known to be essential for vesicle recruitment. We conclude that ATP binding to synapsin IIa plays a key role in modulating its function and in defining its contribution to hippocampal short-term synaptic plasticity.

HDAC2 Selectively Regulates FOXO3a-Mediated Gene Transcription during Oxidative Stress-Induced Neuronal Cell Death

All neurodegenerative diseases are associated with oxidative stress-induced neuronal death. Forkhead box O3a (FOXO3a) is a key transcription factor involved in neuronal apoptosis. However, how FOXO3a forms complexes and functions in oxidative stress processing remains largely unknown. In the present study, we show that histone deacetylase 2 (HDAC2) forms a physical complex with FOXO3a, which plays an important role in FOXO3a-dependent gene transcription and oxidative stress-induced mouse cerebellar granule neuron (CGN) apoptosis. Interestingly, we also found that HDAC2 became selectively enriched in the promoter region of the p21 gene, but not those of other target genes, and inhibited FOXO3a-mediated p21 transcription. Furthermore, we found that oxidative stress reduced the interaction between FOXO3a and HDAC2, leading to an increased histone H4K16 acetylation level in the p21 promoter region and upregulated p21 expression in a manner independent of p53 or E2F1. Phosphorylation of HDAC2 at Ser 394 is important for the HDAC2–FOXO3a interaction, and we found that cerebral ischemia/reperfusion reduced phosphorylation of HDAC2 at Ser 394 and mitigated the HDAC2–FOXO3a interaction in mouse brain tissue. Our study reveals the novel regulation of FOXO3a-mediated selective gene transcription via epigenetic modification in the process of oxidative stress-induced cell death, which could be exploited therapeutically.

Dysregulation of Kv3.4 Channels in Dorsal Root Ganglia Following Spinal Cord Injury

Spinal cord injury (SCI) patients develop chronic pain involving poorly understood central and peripheral mechanisms. Because dysregulation of the voltage-gated Kv3.4 channel has been implicated in the hyperexcitable state of dorsal root ganglion (DRG) neurons following direct injury of sensory nerves, we asked whether such a dysregulation also plays a role in SCI. Kv3.4 channels are expressed in DRG neurons, where they help regulate action potential (AP) repolarization in a manner that depends on the modulation of inactivation by protein kinase C (PKC)-dependent phosphorylation of the channel's inactivation domain. Here, we report that, 2 weeks after cervical hemicontusion SCI, injured rats exhibit contralateral hypersensitivity to stimuli accompanied by accentuated repetitive spiking in putative DRG nociceptors. Also in these neurons at 1 week after laminectomy and SCI, Kv3.4 channel inactivation is impaired compared with naive nonsurgical controls. At 2–6 weeks after laminectomy, however, Kv3.4 channel inactivation returns to naive levels. Conversely, Kv3.4 currents at 2–6 weeks post-SCI are downregulated and remain slow-inactivating. Immunohistochemistry indicated that downregulation mainly resulted from decreased surface expression of the Kv3.4 channel, as whole-DRG-protein and single-cell mRNA transcript levels did not change. Furthermore, consistent with Kv3.4 channel dysregulation, PKC activation failed to shorten the AP duration of small-diameter DRG neurons. Finally, re-expressing synthetic Kv3.4 currents under dynamic clamp conditions dampened repetitive spiking in the neurons from SCI rats. These results suggest a novel peripheral mechanism of post-SCI pain sensitization implicating Kv3.4 channel dysregulation and potential Kv3.4-based therapeutic interventions.

Distribution and Function of HCN Channels in the Apical Dendritic Tuft of Neocortical Pyramidal Neurons

The apical tuft is the most remote area of the dendritic tree of neocortical pyramidal neurons. Despite its distal location, the apical dendritic tuft of layer 5 pyramidal neurons receives substantial excitatory synaptic drive and actively processes corticocortical input during behavior. The properties of the voltage-activated ion channels that regulate synaptic integration in tuft dendrites have, however, not been thoroughly investigated. Here, we use electrophysiological and optical approaches to examine the subcellular distribution and function of hyperpolarization-activated cyclic nucleotide-gated nonselective cation (HCN) channels in rat layer 5B pyramidal neurons. Outside-out patch recordings demonstrated that the amplitude and properties of ensemble HCN channel activity were uniform in patches excised from distal apical dendritic trunk and tuft sites. Simultaneous apical dendritic tuft and trunk whole-cell current-clamp recordings revealed that the pharmacological blockade of HCN channels decreased voltage compartmentalization and enhanced the generation and spread of apical dendritic tuft and trunk regenerative activity. Furthermore, multisite two-photon glutamate uncaging demonstrated that HCN channels control the amplitude and duration of synaptically evoked regenerative activity in the distal apical dendritic tuft. In contrast, at proximal apical dendritic trunk and somatic recording sites, the blockade of HCN channels decreased excitability. Dynamic-clamp experiments revealed that these compartment-specific actions of HCN channels were heavily influenced by the local and distributed impact of the high density of HCN channels in the distal apical dendritic arbor. The properties and subcellular distribution pattern of HCN channels are therefore tuned to regulate the interaction between integration compartments in layer 5B pyramidal neurons.

Role of Parafacial Nuclei in Control of Breathing in Adult Rats

Contiguous brain regions associated with a given behavior are increasingly being divided into subregions associated with distinct aspects of that behavior. Using recently developed neuronal hyperpolarizing technologies, we functionally dissect the parafacial region in the medulla, which contains key elements of the central pattern generator for breathing that are important in central CO₂-chemoreception and for gating active expiration. By transfecting different populations of neighboring neurons with allatostatin or HM₄D G_i/o-coupled receptors, we analyzed the effect of their hyperpolarization on respiration in spontaneously breathing vagotomized urethane-anesthetized rats. We identify two functionally separate parafacial nuclei: ventral (pF_V) and lateral (pF_L). Disinhibition of the pF_L with bicuculline and strychnine led to active expiration. Hyperpolarizing pF_L neurons had no effect on breathing at rest, or changes in inspiratory activity induced by hypoxia and hypercapnia; however, hyperpolarizing pF_L neurons attenuated active expiration when it was induced by hypercapnia, hypoxia, or disinhibition of the pF_L. In contrast, hyperpolarizing pF_V neurons affected breathing at rest by decreasing inspiratory-related activity, attenuating the hypoxia- and hypercapnia-induced increase in inspiratory activity, and when present, reducing expiratory-related abdominal activity. Together with previous observations, we conclude that the pF_V provides a generic excitatory drive to breathe, even at rest, whereas the pF_L is a conditional oscillator quiet at rest that, when activated, e.g., during exercise, drives active expiration.

Decoding a Wide Range of Hand Configurations from Macaque Motor, Premotor, and Parietal Cortices

Despite recent advances in decoding cortical activity for motor control, the development of hand prosthetics remains a major challenge. To reduce the complexity of such applications, higher cortical areas that also represent motor plans rather than just the individual movements might be advantageous. We investigated the decoding of many grip types using spiking activity from the anterior intraparietal (AIP), ventral premotor (F5), and primary motor (M1) cortices. Two rhesus monkeys were trained to grasp 50 objects in a delayed task while hand kinematics and spiking activity from six implanted electrode arrays (total of 192 electrodes) were recorded. Offline, we determined 20 grip types from the kinematic data and decoded these hand configurations and the grasped objects with a simple Bayesian classifier. When decoding from AIP, F5, and M1 combined, the mean accuracy was 50% (using planning activity) and 62% (during motor execution) for predicting the 50 objects (chance level, 2%) and substantially larger when predicting the 20 grip types (planning, 74%; execution, 86%; chance level, 5%). When decoding from individual arrays, objects and grip types could be predicted well during movement planning from AIP (medial array) and F5 (lateral array), whereas M1 predictions were poor. In contrast, predictions during movement execution were best from M1, whereas F5 performed only slightly worse. These results demonstrate for the first time that a large number of grip types can be decoded from higher cortical areas during movement preparation and execution, which could be relevant for future neuroprosthetic devices that decode motor plans.

Contributions of Diverse Excitatory and Inhibitory Neurons to Recurrent Network Activity in Cerebral Cortex

The recurrent synaptic architecture of neocortex allows for self-generated network activity. One form of such activity is the Up state, in which neurons transiently receive barrages of excitatory and inhibitory synaptic inputs that depolarize many neurons to spike threshold before returning to a relatively quiescent Down state. The extent to which different cell types participate in Up states is still unclear. Inhibitory interneurons have particularly diverse intrinsic properties and synaptic connections with the local network, suggesting that different interneurons might play different roles in activated network states. We have studied the firing, subthreshold behavior, and synaptic conductances of identified cell types during Up and Down states in layers 5 and 2/3 in mouse barrel cortex in vitro. We recorded from pyramidal cells and interneurons expressing parvalbumin (PV), somatostatin (SOM), vasoactive intestinal peptide (VIP), or neuropeptide Y. PV cells were the most active interneuron subtype during the Up state, yet the other subtypes also received substantial synaptic conductances and often generated spikes. In all cell types except PV cells, the beginning of the Up state was dominated by synaptic inhibition, which decreased thereafter; excitation was more persistent, suggesting that inhibition is not the dominant force in terminating Up states. Compared with barrel cortex, SOM and VIP cells were much less active in entorhinal cortex during Up states. Our results provide a measure of functional connectivity of various neuron types in barrel cortex and suggest differential roles for interneuron types in the generation and control of persistent network activity.

Changes in Purkinje Cell Simple Spike Encoding of Reach Kinematics during Adaption to a Mechanical Perturbation

The cerebellum is essential in motor learning. At the cellular level, changes occur in both the simple spike and complex spike firing of Purkinje cells. Because simple spike discharge reflects the main output of the cerebellar cortex, changes in simple spike firing likely reflect the contribution of the cerebellum to the adapted behavior. Therefore, we investigated in Rhesus monkeys how the representation of arm kinematics in Purkinje cell simple spike discharge changed during adaptation to mechanical perturbations of reach movements. Monkeys rapidly adapted to a novel assistive or resistive perturbation along the direction of the reach. Adaptation consisted of matching the amplitude and timing of the perturbation to minimize its effect on the reach. In a majority of Purkinje cells, simple spike firing recorded before and during adaptation demonstrated significant changes in position, velocity, and acceleration sensitivity. The timing of the simple spike representations change within individual cells, including shifts in predictive versus feedback signals. At the population level, feedback-based encoding of position increases early in learning and velocity decreases. Both timing changes reverse later in learning. The complex spike discharge was only weakly modulated by the perturbations, demonstrating that the changes in simple spike firing can be independent of climbing fiber input. In summary, we observed extensive alterations in individual Purkinje cell encoding of reach kinematics, although the movements were nearly identical in the baseline and adapted states. Therefore, adaption to mechanical perturbation of a reaching movement is accompanied by widespread modifications in the simple spike encoding.

Functional Mapping of Face-Selective Regions in the Extrastriate Visual Cortex of the Marmoset

The cerebral cortex of humans and macaques has specialized regions for processing faces and other visual stimulus categories. It is unknown whether a similar functional organization exists in New World monkeys, such as the common marmoset (Callithrix jacchus), a species of growing interest as a primate model in neuroscience. To address this question, we measured selective neural responses in the brain of four awake marmosets trained to fix their gaze upon images of faces, bodies, objects, and control patterns. In two of the subjects, we measured high gamma-range field potentials from electrocorticography arrays implanted over a large portion of the occipital and inferotemporal cortex. In the other two subjects, we measured BOLD fMRI responses across the entire brain. Both techniques revealed robust, regionally specific patterns of category-selective neural responses. We report that at least six face-selective patches mark the occipitotemporal pathway of the marmoset, with the most anterior patches showing the strongest preference for faces over other stimuli. The similar appearance of these patches to previous findings in macaques and humans, including their apparent arrangement in two parallel pathways, suggests that core elements of the face processing network were present in the common anthropoid primate ancestor living ~35 million years ago. The findings also identify the marmoset as a viable animal model system for studying specialized neural mechanisms related to high-level social visual perception in humans.

Corticospinal Tract Development and Spinal Cord Innervation Differ between Cervical and Lumbar Targets

The corticospinal (CS) tract is essential for voluntary movement, but what we know about the organization and development of the CS tract remains limited. To determine the total cortical area innervating the seventh cervical spinal cord segment (C7), which controls forelimb movement, we injected a retrograde tracer (fluorescent microspheres) into C7 such that it would spread widely within the unilateral gray matter (to >80%), but not to the CS tract. Subsequent detection of the tracer showed that, in both juvenile and adult mice, neurons distributed over an unexpectedly broad portion of the rostral two-thirds of the cerebral cortex converge to C7. This even included cortical areas controlling the hindlimbs (the fourth lumbar segment, L4). With aging, cell densities greatly declined, mainly due to axon branch elimination. Whole-cell recordings from spinal cord cells upon selective optogenetic stimulation of CS axons, and labeling of axons (DsRed) and presynaptic structures (synaptophysin) through cotransfection using exo utero electroporation, showed that overgrowing CS axons make synaptic connections with spinal cells in juveniles. This suggests that neuronal circuits involved in the CS tract to C7 are largely reorganized during development. By contrast, the cortical areas innervating L4 are limited to the conventional hindlimb area, and the cell distribution and density do not change during development. These findings call for an update of the traditional notion of somatotopic CS projection and imply that there are substantial developmental differences in the cortical control of forelimb and hindlimb movements, at least in rodents.

Interplay of Inhibition and Excitation Shapes a Premotor Neural Sequence

In the zebra finch, singing behavior is driven by a sequence of bursts within premotor neurons located in the forebrain nucleus HVC (proper name). In addition to these excitatory projection neurons, HVC also contains inhibitory interneurons with a role in premotor patterning that is unclear. Here, we used a range of electrophysiological and behavioral observations to test previously described models suggesting discrete functional roles for inhibitory interneurons in song production. We show that single HVC premotor neuron bursts are sufficient to drive structured activity within the interneuron network because of pervasive and facilitating synaptic connections. We characterize interneuron activity during singing and describe reliable pauses in the firing of those neurons. We then demonstrate that these gaps in inhibition are likely to be necessary for driving normal bursting behavior in HVC premotor neurons and suggest that structured inhibition and excitation may be a general mechanism enabling sequence generation in other circuits.

Musical Training Orchestrates Coordinated Neuroplasticity in Auditory Brainstem and Cortex to Counteract Age-Related Declines in Categorical Vowel Perception

Musicianship in early life is associated with pervasive changes in brain function and enhanced speech-language skills. Whether these neuroplastic benefits extend to older individuals more susceptible to cognitive decline, and for whom plasticity is weaker, has yet to be established. Here, we show that musical training offsets declines in auditory brain processing that accompanying normal aging in humans, preserving robust speech recognition late into life. We recorded both brainstem and cortical neuroelectric responses in older adults with and without modest musical training as they classified speech sounds along an acoustic–phonetic continuum. Results reveal higher temporal precision in speech-evoked responses at multiple levels of the auditory system in older musicians who were also better at differentiating phonetic categories. Older musicians also showed a closer correspondence between neural activity and perceptual performance. This suggests that musicianship strengthens brain-behavior coupling in the aging auditory system. Last, "neurometric" functions derived from unsupervised classification of neural activity established that early cortical responses could accurately predict listeners' psychometric speech identification and, more critically, that neurometric profiles were organized more categorically in older musicians. We propose that musicianship offsets age-related declines in speech listening by refining the hierarchical interplay between subcortical/cortical auditory brain representations, allowing more behaviorally relevant information carried within the neural code, and supplying more faithful templates to the brain mechanisms subserving phonetic computations. Our findings imply that robust neuroplasticity conferred by musical training is not restricted by age and may serve as an effective means to bolster speech listening skills that decline across the lifespan.

A53T Human {alpha}-Synuclein Overexpression in Transgenic Mice Induces Pervasive Mitochondria Macroautophagy Defects Preceding Dopamine Neuron Degeneration

In vitro evidence suggests that the inefficient removal of damaged mitochondria by macroautophagy contributes to Parkinson's disease (PD). Using a tissue-specific gene amplification strategy, we generated a transgenic mouse line with human α-synuclein A53T overexpression specifically in dopamine (DA) neurons. Transgenic mice showed profound early-onset mitochondria abnormalities, characterized by macroautophagy marker-positive cytoplasmic inclusions containing mainly mitochondrial remnants, which preceded the degeneration of DA neurons. Genetic deletion of either parkin or PINK1 in these transgenic mice significantly worsened mitochondrial pathologies, including drastically enlarged inclusions and loss of total mitochondria contents. These data suggest that mitochondria are the main targets of α-synuclein and their defective autophagic clearance plays a significant role during pathogenesis. Moreover, endogenous PINK1 or parkin is indispensable for the proper autophagic removal of damaged mitochondria. Our data for the first time establish an essential link between mitochondria macroautophagy impairments and DA neuron degeneration in an in vivo model based on known PD genetics. The model, its well-defined pathologies, and the demonstration of a main pathogenesis pathway in the present study have set the stage and direction of emphasis for future studies.

Evidence for Consolidation of Neuronal Assemblies after Seizures in Humans

The Full-Length Form of the Drosophila Amyloid Precursor Protein Is Involved in Memory Formation

The APP plays a central role in AD, a pathology that first manifests as a memory decline. Understanding the role of APP in normal cognition is fundamental in understanding the progression of AD, and mammalian studies have pointed to a role of secreted APPα in memory. In Drosophila, we recently showed that APPL, the fly APP ortholog, is required for associative memory. In the present study, we aimed to characterize which form of APPL is involved in this process. We show that expression of a secreted-APPL form in the mushroom bodies, the center for olfactory memory, is able to rescue the memory deficit caused by APPL partial loss of function. We next assessed the impact on memory of the Drosophila α-secretase kuzbanian (KUZ), the enzyme initiating the nonamyloidogenic pathway that produces secreted APPLα. Strikingly, KUZ overexpression not only failed to rescue the memory deficit caused by APPL loss of function, it exacerbated this deficit. We further show that in addition to an increase in secreted-APPL forms, KUZ overexpression caused a decrease of membrane-bound full-length species that could explain the memory deficit. Indeed, we observed that transient expression of a constitutive membrane-bound mutant APPL form is sufficient to rescue the memory deficit caused by APPL reduction, revealing for the first time a role of full-length APPL in memory formation. Our data demonstrate that, in addition to secreted APPL, the noncleaved form is involved in memory, raising the possibility that secreted and full-length APPL act together in memory processes.

Desynchronization of Fast-Spiking Interneurons Reduces {beta}-Band Oscillations and Imbalance in Firing in the Dopamine-Depleted Striatum

Oscillations in the β-band (8–30 Hz) that emerge in the output nuclei of the basal ganglia during Parkinson's disease, along with an imbalanced activation of the direct and indirect pathways, have been linked to the hypokinetic motor output associated with the disease. Although dopamine depletion causes a change in cellular and network properties in the striatum, it is unclear whether abnormal activity measured in the globus pallidus and substantia nigra pars reticulata is caused by abnormal striatal activity. Here we use a computational network model of medium spiny neurons (MSNs)—fast-spiking interneurons (FSIs), based on data from several mammalian species, and find that robust β-band oscillations and imbalanced firing emerge from implementation of changes to cellular and circuit properties caused by dopamine depletion. These changes include a reduction in connections between MSNs, a doubling of FSI inhibition to D₂ MSNs, an increase in D₂ MSN dendritic excitability, and a reduction in D₂ MSN somatic excitability. The model reveals that the reduced decorrelation between MSNs attributable to weakened lateral inhibition enables the strong influence of synchronous FSIs on MSN firing and oscillations. Weakened lateral inhibition also produces an increased sensitivity of MSN output to cortical correlation, a condition relevant to the parkinsonian striatum. The oscillations of FSIs, in turn, are strongly modulated by fast electrical transmission between FSIs through gap junctions. These results suggest that pharmaceuticals that desynchronize FSI activity may provide a novel treatment for the enhanced β-band oscillations, imbalanced firing, and motor dysfunction in Parkinson's disease.

The Potent BACE1 Inhibitor LY2886721 Elicits Robust Central A{beta} Pharmacodynamic Responses in Mice, Dogs, and Humans

BACE1 is a key protease controlling the formation of amyloid β, a peptide hypothesized to play a significant role in the pathogenesis of Alzheimer's disease (AD). Therefore, the development of potent and selective inhibitors of BACE1 has been a focus of many drug discovery efforts in academia and industry. Herein, we report the nonclinical and early clinical development of LY2886721, a BACE1 active site inhibitor that reached phase 2 clinical trials in AD. LY2886721 has high selectivity against key off-target proteases, which efficiently translates in vitro activity into robust in vivo amyloid β lowering in nonclinical animal models. Similar potent and persistent amyloid β lowering was observed in plasma and lumbar CSF when single and multiple doses of LY2886721 were administered to healthy human subjects. Collectively, these data add support for BACE1 inhibition as an effective means of amyloid lowering and as an attractive target for potential disease modification therapy in AD.

Chronic Oligodendrogenesis and Remyelination after Spinal Cord Injury in Mice and Rats

Adult progenitor cells proliferate in the acutely injured spinal cord and their progeny differentiate into new oligodendrocytes (OLs) that remyelinate spared axons. Whether this endogenous repair continues beyond the first week postinjury (wpi), however, is unknown. Identifying the duration of this response is essential for guiding therapies targeting improved recovery from spinal cord injury (SCI) by enhancing OL survival and/or remyelination. Here, we used two PDGFRα-reporter mouse lines and rats injected with a GFP-retrovirus to assess progenitor fate through 80 d after injury. Surprisingly, new OLs were generated as late as 3 months after injury and their processes ensheathed axons near and distal to the lesion, colocalized with MBP, and abutted Caspr+ profiles, suggesting newly formed myelin. Semithin sections confirmed stereotypical thin OL remyelination and few bare axons at 10 wpi, indicating that demyelination is relatively rare. Astrocytes in chronic tissue expressed the pro-OL differentiation and survival factors CNTF and FGF-2. In addition, pSTAT3+ NG2 cells were present through at least 5 wpi, revealing active signaling of the Jak/STAT pathway in these cells. The progenitor cell fate genes Sox11, Hes5, Id2, Id4, BMP2, and BMP4 were dynamically regulated for at least 4 wpi. Collectively, these data verify that the chronically injured spinal cord is highly dynamic. Endogenous repair, including oligodendrogenesis and remyelination, continues for several months after SCI, potentially in response to growth factors and/or transcription factor changes. Identifying and understanding spontaneous repair processes such as these is important so that beneficial plasticity is not inadvertently interrupted and effort is not exerted to needlessly duplicate ongoing spontaneous repair.