bioRxiv Subject Collection: Neuroscience's Journal

Stable, chronic in-vivo recordings from a fully wireless subdural-contained 65,536-electrode brain-computer interface device
Minimally invasive, high-bandwidth brain-computer-interface (BCI) devices can revolutionize human applications. With orders-of-magnitude improvements in volumetric efficiency over other BCI technologies, we developed a 50-m-thick, mechanically flexible micro-electrocorticography (ECoG) BCI, integrating 256x256 electrodes, signal processing, data telemetry, and wireless powering on a single complementary metal-oxide-semiconductor (CMOS) substrate containing 65,536 recording and 16,384 stimulation channels, from which we can simultaneously record up to 1024 channels at a given time. Fully implanted below the dura, our chip is wirelessly powered, communicating bi-directionally with an external relay station outside the body. We demonstrated chronic, reliable recordings for up to two weeks in pigs and up to two months in behaving non-human primates from somatosensory, motor, and visual cortices, decoding brain signals at high spatiotemporal resolution.

Reconciling Flexibility and Efficiency: Medial Entorhinal Cortex Represents a Compositional Cognitive Map
The influential concept of a cognitive map envisions that the brain builds mental representations of objects, barriers, and goals. This idea has been formalized in a range of computational models that show how such representations can be useful for guiding goal-directed behavior, for instance by planning novel routes to maximize long-run rewards. One key feature of flexible cognitive representations generally is that they exploit compositionality -the ability to build complex structures by recombining simpler parts. However, how this principle plays out in neural representations of cognitive maps and map-based planning remains largely unexplored. Indeed, as we show here, compositionality can be difficult to reconcile with efficient planning: because reuse tends to oppose flexibility, it is challenging to construct a compositional representation of the environment which is also organized in a way that enables generalizability and efficient planning. Here, we propose a novel model for efficiently creating and planning with compositional predictive maps, and further show that it successfully simulates various aspects of response fields in the medial entorhinal cortex, particularly object vector cells and grid cells. The model treats each object as an alteration to a baseline map linked to open space, creating complete predictive maps by combining object-related representations compositionally. Overall, this work provides a comprehensive and realistic model for efficient model learning and model-based planning in animals, and offers insights into the brain processes supporting efficient, flexible planning using compositional predictive maps.

Regulation of Neuronal Chloride Homeostasis by Pro- and Mature Brain-Derived Neurotrophic Factor (BDNF) via KCC2 Cation-Chloride Cotransporters in Rat Cortical Neurons
The strength of inhibitory neurotransmission depends on intracellular neuronal chloride concentration, primarily regulated by the activity of cation-chloride cotransporters NKCC1 and KCC2. Brain-derived neurotrophic factor (BDNF) influences the functioning of these co-transporters. BDNF is synthesized from precursor proteins (proBDNF), which undergo proteolytic cleavage to yield mature BDNF (mBDNF). While previous studies have indicated the involvement of BDNF signaling in the activity of KCC2, its specific mechanisms are unclear. We investigated the interplay between both forms of BDNF and chloride homeostasis in rat hippocampal neurons and in-utero electroporated cortices of rat pups, spanning the behavioral, cellular, and molecular levels. We found that both pro- and mBDNF play a comparable role in immature neurons by inhibiting the capacity of neurons to extrude chloride. Additionally, proBDNF increases the endocytosis of KCC2 while maintaining a depolarizing shift of EGABA in maturing neurons. Behaviorally, proBDNF-electroporated rat pups in the somatosensory cortex exhibit sensory deficits delayed huddling and cliff avoidance. These findings emphasize the role of BDNF signaling in regulating chloride transport through the modulation of KCC2. In summary, this study provides valuable insights into the intricate interplay between BDNF, chloride homeostasis, and inhibitory synaptic transmission, shedding light on the underlying cellular mechanisms involved.

Valence ambiguity dynamically shapes striatal dopamine heterogeneity
Adaptive decision making relies on dynamic updating of learned associations where environmental cues come to predict positive and negatively valenced stimuli, such as food or threat. Flexible cue-guided behaviors depend on a network of brain systems, including dopamine signaling in the striatum, which is critical for learning and maintenance of conditioned behaviors. Critically, it remains unclear how dopamine signaling encodes multi-valent, dynamic learning contexts, where positive and negative associations must be rapidly disambiguated. To understand this, we employed a Pavlovian discrimination paradigm, where cues predicting positive and negative outcomes were intermingled during conditioning sessions, and their meaning was serially reversed across training. We found that rats readily distinguished these cues, and updated their behavior rapidly upon valence reversal. Using fiber photometry, we recorded dopamine signaling in three major striatal subregions - the dorsolateral striatum (DLS), the nucleus accumbens core, and the nucleus accumbens medial shell - and found heterogeneous responses to positive and negative conditioned cues and their predicted outcomes. Valence ambiguity introduced by cue reversal reshaped striatal dopamine on different timelines: nucleus accumbens core and shell signals updated more readily than those in the DLS. Together, these results suggest that striatal dopamine flexibly encodes multi-valent learning contexts, and these signals are dynamically modulated by changing contingencies to resolve ambiguity about the meaning of environmental cues.

TMS-based neurofeedback training of mental finger individuation induces neuroplastic changes in the sensorimotor cortex
Neurofeedback (NF) training based on motor imagery is increasingly used in neurorehabilitation with the aim to improve motor functions. However, the neuroplastic changes underpinning these improvements are poorly understood. Here, we used mental finger individuation, i.e., the selective facilitation of single finger representations without producing overt movements, as a model to study neuroplasticity induced by NF. To enhance mental finger individuation, we used transcranial magnetic stimulation (TMS)-based NF training. During motor imagery of individual finger movements, healthy participants were provided visual feedback on the size of motor evoked potentials, reflecting their finger-specific corticospinal excitability. We found that TMS-NF improved the top-down activation of finger-specific representations. First, intracortical inhibitory circuits in the primary motor cortex were tuned after training such that inhibition was selectively reduced for the finger that was mentally activated. Second, motor imagery finger representations in sensorimotor areas assessed with functional MRI became more distinct after training. Together, our results indicate that the neural underpinnings of finger individuation, a well-known model system for neuroplasticity, can be modified using TMS-NF guided motor imagery training. These findings demonstrate that TMS-NF induces neuroplasticity in the sensorimotor system, highlighting the promise of TMS-NF on the recovery of fine motor function.

High delay discounting relates to core symptoms and to pulvinar atrophy in frontotemporal dementia
Behavioural variant frontotemporal dementia (bvFTD) is a neurodegenerative disorder characterized by behavioural changes and atrophy in brain regions important for decision-making. Computations such as trading off between larger later (LL) and smaller sooner (SS) rewards, called delay discounting in behavioural economics, might be heavily impaired by bvFTD. In this cross-sectional study, our objectives were to investigate (1) whether bvFTD patients show higher delay discounting than healthy controls, (2) whether this maladaptive discounting correlates with impulsivity-related bvFTD symptoms, and (3) in which brain regions atrophy is related to bvFTD's steeper discounting. BvFTD patients (N=24) and matched controls (N=18) performed two delay discounting tasks: one with monetary rewards and one with food rewards. We compared discount rates (log(k)) in bvFTD patients and controls and tested their correlations with symptoms. We used participants' structural MRI data and applied whole-brain mediation analyses to investigate brain structures mediating the effect of bvFTD on delay discounting. For both monetary and food rewards, delay discounting was significantly higher in bvFTD patients than in healthy controls. BvFTD patients' higher discounting of both money and food was associated with their greater disinhibition and eating behaviour changes. Whole-brain mediation analyses revealed that (1) several brain regions (left thalamic pulvinar, left parahippocampal cortex, right temporal lobe) were predictive of steeper discounting of both money and food and (2) grey matter density in these brain regions, including most prominently the medial pulvinar, mediated the effect of bvFTD on discounting. The impulsive preference for sooner rewards captured by delay discounting might constitute a common mechanism of the behavioural symptoms of inhibition deficit and eating behaviour changes in bvFTD. Future studies could further investigate the potential role of medial pulvinar structural modifications as a transdiagnostic marker and a therapeutic target of impulsivity troubles.

Developmental olfactory dysfunction and abnormal odor memory in immune-challenged Disc1+/- mice
Neuronal activity in the olfactory bulb (OB) drives coordinated activity in the hippocampal-prefrontal network during early development. Inhibiting OB output in neonatal mice disrupts functional development of the hippocampal formation as well as cognitive abilities. These impairments manifest early in life and resemble dysfunctions of the hippocampus and the prefrontal cortex that have been linked to neuropsychiatric disorders. Thus, we investigated a disease mouse model and asked whether activity in the OB might be altered, thereby contributing to the dysfunctional development of the hippocampal-prefrontal network. We addressed this question by combining in vivo electrophysiology with behavioral assessment of immune-challenged Disc1+/- mice that mimic the dual genetic-environmental etiology of neuropsychiatric disorders. In wildtype mice, we found high DISC1 expression levels in OB projection neurons during development. Furthermore, neuronal and network activity in the OB, as well as the drive from the bulb to the hippocampal-prefrontal network were reduced in immune-challenged Disc1+/- mice during early development. This early deficit did not affect odor-evoked activity and odor perception but resulted in impaired long-term odor memory. We propose that reduced endogenous activity in the developing OB contributes to altered maturation of the hippocampal-prefrontal network, leading to memory impairment in immune-challenged Disc1+/- mice.

Mapping vascular network architecture in primate brain using ferumoxytol-weighted laminar MRI
Mapping the vascular organization of the brain is of great importance across various domains of basic neuroimaging research, diagnostic radiology, and neurology. However, the intricate task of precisely mapping vasculature across brain regions and cortical layers presents formidable challenges, resulting in a limited understanding of neurometabolic factors influencing the brains microvasculature. Addressing this gap, our study investigates whole-brain vascular volume using ferumoxytol-weighted laminar-resolution multi-echo gradient-echo imaging in macaque monkeys. We validate the results with published data for vascular densities and compare them with cytoarchitecture, neuron and synaptic densities. The ferumoxytol-induced change in transverse relaxation rate ({Delta}R2*), an indirect proxy measure of cerebral blood volume (CBV), was mapped onto twelve equivolumetric laminar cortical surfaces. Our findings reveal that CBV varies 3-fold across the brain, with the highest vascular volume observed in the inferior colliculus and lowest in the corpus callosum. In the cerebral cortex, CBV is notably high in early primary sensory areas and low in association areas responsible for higher cognitive functions. Classification of CBV into distinct groups unveils extensive replication of translaminar vascular network motifs, suggesting distinct computational energy supply requirements in areas with varying cytoarchitecture types. Regionally, baseline R2* and CBV exhibit positive correlations with neuron density and negative correlations with receptor densities. Adjusting image resolution based on the critical sampling frequency of penetrating cortical vessels, allows us to delineate approximately 30% of the arterial-venous vessels. Collectively, these results mark significant methodological and conceptual advancements, contributing to the refinement of cerebrovascular MRI. Furthermore, our study establishes a linkage between neurometabolic factors and the vascular network architecture in the primate brain.

Electrophysiological correlates of visual memory search
In everyday life, we frequently engage in hybrid search, where we look for multiple items stored in memory (e.g., a mental shopping list) in our visual environment. Across three experiments, we used event-related potentials to better understand the contributions of visual working memory (VWM) and long-term memory (LTM) during the memory search component of hybrid search. Experiments 1 and 2 demonstrated that the FN400, an index of LTM recognition, and the CDA, an index of VWM, increased with memory set size (target load), suggesting that both VWM and LTM are involved in memory search, even when memory load exceeds capacity limitations of VWM. In Experiment 3, we used these electrophysiological indices to test how categorical similarity of targets and distractors affects memory search. The CDA and FN400 were modulated by memory set size only if items resembled targets. This suggests that dissimilar distractor items can be rejected before eliciting a memory search. Together, our findings demonstrate the interplay of VWM and LTM processes during memory search for multiple targets.

Brain-wide functional connectome analysis of 40,000 individuals reveals brain networks that show aging effects in older adults
The functional connectome changes with aging. We systematically evaluated aging related alterations in the functional connectome using a whole-brain connectome network analysis in 39,675 participants in UK Biobank project. We used adaptive dense network discovery tools to identify networks directly associated with aging from resting-state fMRI data. We replicated our findings in 499 participants from the Lifespan Human Connectome Project in Aging study. The results consistently revealed two motor-related subnetworks (both permutation test p-values <0.001) that showed a decline in resting-state functional connectivity (rsFC) with increasing age. The first network primarily comprises sensorimotor and dorsal/ventral attention regions from precentral gyrus, postcentral gyrus, superior temporal gyrus, and insular gyrus, while the second network is exclusively composed of basal ganglia regions, namely the caudate, putamen, and globus pallidus. Path analysis indicates that white matter fractional anisotropy mediates 19.6% (p<0.001, 95% CI [7.6% 36.0%]) and 11.5% (p<0.001, 95% CI [6.3% 17.0%]) of the age-related decrease in both networks, respectively. The total volume of white matter hyperintensity mediates 32.1% (p<0.001, 95% CI [16.8% 53.0%]) of the aging-related effect on rsFC in the first subnetwork.

Anterior pituitary gland volume mediates associations between pubertal hormones and changes in transdiagnostic symptoms in youth
The pituitary gland (PG) plays a central role in the production and secretion of pubertal hormones, with documented links to the emergence and increase in mental health symptoms known to occur during adolescence. Although much of the literature has focused on examining whole PG volume, recent findings suggest that there are associations among pubertal hormone levels, including dehydroepiandrosterone (DHEA), subregions of the PG, and elevated mental health symptoms (e.g., internalizing symptoms) during adolescence. Surprisingly, studies have not yet examined associations among these factors and increasing transdiagnostic symptomology, despite DHEA being a primary output of the anterior PG. Therefore, the current study sought to fill this gap by examining whether anterior PG volume specifically mediates associations between DHEA levels and changes in dysregulation symptoms in an adolescent sample (N = 114, 9-17 years, Mage = 12.87, SD = 1.88). Following manual tracing of the anterior and posterior PG, structural equation modeling revealed that greater anterior, not posterior, PG volume mediated the association between greater DHEA levels and increasing dysregulation symptoms across time, controlling for baseline dysregulation symptom levels. These results suggest specificity in the role of the anterior PG in adrenarcheal processes that may confer risk for psychopathology during adolescence. This work not only highlights the importance of separately tracing the anterior and posterior PG, but also suggests that transdiagnostic factors like dysregulation are useful in parsing hormone-related increases in mental health symptoms in youth.

Age-related constraints on the spatial geometry of the brain
Age-related structural brain changes may be better captured by assessing complex spatial geometric differences rather than isolated changes to individual regions. We applied a novel analytic method to quantify age-related changes to the spatial anatomy of the brain by measuring expansion and compression of global brain shape and the distance between cross-hemisphere homologous regions. To test how global brain shape and regional distances are affected by aging, we analyzed 2,603 structural MRIs (range: 30-97 years). Increasing age was associated with global shape expansion across inferior-anterior gradients, global compression across superior-posterior gradients, and regional expansion between frontotemporal homologues. Specific patterns of global and regional expansion and compression were further associated with clinical impairment and distinctly related to deficits in various cognitive domains. These findings suggest that changes to the complex spatial anatomy and geometry of the aging brain may be associated with reduced efficiency and cognitive dysfunction in older adults.

Examining speech-brain tracking during early bidirectional, free-flowing caregiver-infant interactions
Neural entrainment to slow modulations in the amplitude envelope of infant-directed speech is thought to drive early language learning. Most previous research with infants examining speech-brain tracking has been conducted in controlled, experimental settings, which are far from the complex environments of everyday interactions. Whilst recent work has begun to investigate speech-brain tracking to naturalistic speech, this work has been conducted in semi-structured paradigms, where infants listen to live adult speakers, without engaging in free-flowing social interactions. Here, we test the applicability of mTRF modelling to measure speech-brain tracking in naturalistic and bidirectional free-play interactions of 9-12-month-olds with their caregivers. Using a backwards modelling approach, we test individual and generic training procedures, and examine the effects of data quantity and quality on model fitting. We show model fitting is most optimal using an individual approach, trained on continuous segments of interaction data. Corresponding to previous findings, individual models showed significant speech-brain tracking at delta modulation frequencies, but not in alpha and theta bands. These findings open new methods for studying the interpersonal micro-processes that support early language learning. In future work, it will be important to develop a mechanistic framework for understanding how our brains track naturalistic speech during infancy.

Aging leads to sex-dependent effects on pair bonding and increased number of oxytocin-producing neurons in monogamous prairie voles
Pair bonds powerfully modulate health, which becomes particularly important when facing the detrimental effects of aging. To examine the impact of aging on relationship formation and response to loss, we examined behavior in 6-, 12-, and 18-month male and female prairie voles, a monogamous species that forms mating-based pair bonds. We found that older males (18-months) bonded quicker than younger voles, while similarly aged female voles increased partner directed affiliative behaviors. Supporting sex differences in bonding behaviors, we found that males were more likely to sample both partner and novel voles while females were more likely to display partner preference during the initial 20 minutes of the test. Using partner separation to study loss, we observed an erosion of partner preference only in 12-month females, but an overall decrease in partner-directed affiliation in females across all groups, but not in males. Finally, we found that the number of oxytocin, but not vasopressin, cells in the paraventricular hypothalamus increased during aging. These results establish prairie voles as a novel model to study the effects of normal and abnormal aging on pair bonding.

Comparison of MR coil options for concurrent TMS-fMRI
Concurrent transcranial magnetic stimulation (TMS) with functional magnetic resonance imaging (fMRI) is increasingly being used to study how TMS affects neural processing in local and remote connected brain regions. However, there are many technical challenges that arise when operating this unique combination of techniques. One such challenge is MR head coil compatibility and the image resolution that can be achieved. Here we compare the temporal-signal-to noise-ratio (tSNR) between 3 different MR head coils that can be used with TMS. We show that the 7-channel TMS-dedicated surface coils result in a very high tSNR directly under the TMS and the supplementary coil in comparison to the TxRx and the Magnetica. However, there is low tSNR elsewhere. This field inhomogeneity may not be suitable for all research questions, for example where the aim is to look at distributed neural responses. In these cases, an MR coil with a more homogeneous tSNR such as the Magnetica, may be more appropriate.

A stochastic RNA editing process targets a limited number of sites in individual Drosophila glutamatergic motoneurons
RNA editing is a post-transcriptional source of protein diversity and occurs across the animal kingdom. Given the complete profile of mRNA targets and their editing rate in individual cells is unclear, we analyzed single cell RNA transcriptomes from Drosophila larval tonic and phasic glutamatergic motoneuron subtypes to determine the most highly edited targets and identify cell-type specific editing. From ~15,000 genes encoded in the genome, 316 high confidence A-to-I canonical RNA edit sites were identified, with 102 causing missense amino acid changes in proteins regulating membrane excitability, synaptic transmission, and cellular function. Some sites showed 100% editing in single neurons as observed with mRNAs encoding mammalian AMPA receptors. However, most sites were edited at lower levels and generated variable expression of edited and unedited mRNAs within individual neurons. Together, these data provide insights into how the RNA editing landscape alters protein function to modulate the properties of two well-characterized neuronal populations in Drosophila.

Phase synchrony between prefrontal noradrenergic and cholinergic signals indexes inhibitory control
Inhibitory control is a critical executive function that allows animals to suppress their impulsive behavior in order to achieve certain goals or avoid punishment. We investigated norepinephrine (NE) and acetylcholine (ACh) dynamics and population neuronal activity in the prefrontal cortex during inhibitory control. Using fluorescent sensors to measure extracellular levels of NE and ACh, we simultaneously recorded the dynamics of prefrontal NE and ACh in mice performing an inhibitory control task. The prefrontal NE and ACh signals exhibited strong coherence at 0.4-0.8 Hz. Chemogenetic inhibition of locus coeruleus (LC) neurons that project to the basal forebrain region reduced inhibitory control performance to chance levels. However, this manipulation did not diminish the difference in NE/ACh signals between successful and failed trials; instead, it abolished the difference in NE-ACh phase synchrony between the successful and failed trials, indicating that NE-ACh phase synchrony is a task-relevant neuromodulatory feature. Chemogenetic inhibition of cholinergic neurons that project to the LC region did not impair the inhibitory control performance, nor did it abolish the difference in NE-ACh phase synchrony between successful or failed trials, further confirming the relevance of NE-ACh phase synchrony to inhibitory control. To understand the possible effect of NE-ACh synchrony on prefrontal population activity, we employed Neuropixels to record from the prefrontal cortex with and without inhibiting LC neurons that project to the basal forebrain during inhibitory control. The LC inhibition reduced the number of prefrontal neurons encoding inhibitory control. Demixed principal component analysis (dPCA) further revealed that population firing patterns representing inhibitory control were impaired by the LC inhibition. Disparities in NE-ACh phase synchrony relevant to inhibitory control occurred only in the prefrontal cortex, but not in the parietal cortex, somatosensory cortex, and the somatosensory thalamus. Taken together, these findings suggest that the LC modulates inhibitory control through its collective effect with cholinergic systems on population activity in the prefrontal cortex. Our results further revealed that NE-ACh phase synchrony is a critical neuromodulatory feature with important implications for cognitive control.

Epidural Spinal Cord Recordings (ESRs): Sources of Artifact in Stimulation Evoked Compound Action Potentials
Introduction: Evoked compound action potentials (ECAPs) measured using epidural spinal recordings (ESRs) during epidural spinal cord stimulation (SCS) can help elucidate fundamental mechanisms for the treatment of pain, as well as inform closed-loop control of SCS. Previous studies have used ECAPs to characterize the neural response to various neuromodulation therapies and have demonstrated that ECAPs are highly prone to multiple sources of artifact, including post-stimulus pulse capacitive artifact, electromyography (EMG) bleed-through, and motion artifact resulting from disturbance of the electrode/tissue interface during normal behavior. However, a thorough characterization has yet to be performed for how these sources of artifact may contaminate recordings within the temporal window commonly used to determine activation of A-beta fibers in a large animal model. Methods: We characterized the sources of artifacts that can contaminate the recording of ECAPs in an epidural SCS swine model using the Abbott Octrode lead. Muscle paralytics were administered to block muscle activation preventing EMG from contaminating the recorded ECAPs. Concurrent EMG recordings of the longissimus, a long muscle of the back, were used to confirm a 2-4 millisecond (ms) latency source of EMG bleed-through that frequently contaminated the A-beta temporal window. Additionally, we obtained recordings approximately 5-10 minutes post-mortem after clear evoked A-beta and associated EMG responses ceased to characterize the representation of stimulation artifact across the array. Results: Spinal ECAP recordings can be contaminated by capacitive artifact, short latency EMG from nearby long muscles of the back, and motion artifact from multiple sources. In many cases, the capacitive artifact can appear nearly identical in duration and waveshape to evoked A-beta responses. These sources of EMG can have phase shifts across the electrode array, very similar to the phase shift anticipated by propagation of an evoked A-beta fiber response across the array. This short latency EMG is often evident at currents similar to those needed to activate A-beta fibers associated with the treatment of pain. Changes in cerebrospinal fluid between the cord and dura, and motion induced during breathing created a cyclic oscillation in all evoked components of the recorded ECAP signal. Conclusion: Careful controls must be implemented to accurately separate neural signal from the sources of artifact in spinal cord ECAPs. To address this, we suggest experimental procedures and associated reporting requirements necessary to disambiguate the underlying neural response from these confounds. These data are important to better understand the conceptual framework for recorded ESRs, with components such as ECAPs, EMG responses and artifacts, and have important implications for closed-loop control algorithms to account for transient motion such as postural changes and cough.

A chromosome region linked to neurodevelopmental disorders acts in distinct neuronal circuits in males and females to control locomotor behavior
Biological sex shapes the manifestation and progression of neurodevelopmental disorders (NDDs). These disorders often demonstrate male-specific vulnerabilities; however, the identification of underlying mechanisms remains a significant challenge in the field. Hemideletion of the 16p11.2 region (16p11.2 del/+) is associated with NDDs, and mice modeling 16p11.2 del/+ exhibit sex-specific striatum-related phenotypes relevant to NDDs. Striatal circuits, crucial for locomotor control, consist of two distinct pathways: the direct and indirect pathways originating from D1 dopamine receptor (D1R) and D2 dopamine receptor (D2R) expressing spiny projection neurons (SPNs), respectively. In this study, we define the impact of 16p11.2 del/+ on striatal circuits in male and female mice. Using snRNA-seq, we identify sex- and cell type-specific transcriptomic changes in the D1- and D2-SPNs of 16p11.2 del/+ mice, indicating distinct transcriptomic signatures in D1-SPNs and D2-SPNs in males and females, with a ~5-fold greater impact in males. Further pathway analysis reveals differential gene expression changes in 16p11.2 del/+ male mice linked to synaptic plasticity in D1- and D2-SPNs and GABA signaling pathway changes in D1-SPNs. Consistent with our snRNA-seq study revealing changes in GABA signaling pathways, we observe distinct changes in miniature inhibitory postsynaptic currents (mIPSCs) in D1- and D2-SPNs from 16p11.2 del/+ male mice. Behaviorally, we utilize conditional genetic approaches to introduce the hemideletion selectively in either D1- or D2-SPNs and find that conditional hemideletion of genes in the 16p11.2 region in D2-SPNs causes hyperactivity in male mice, but hemideletion in D1-SPNs does not. Within the striatum, hemideletion of genes in D2-SPNs in the dorsal lateral striatum leads to hyperactivity in males, demonstrating the importance of this striatal region. Interestingly, conditional 16p11.2 del/+ within the cortex drives hyperactivity in both sexes. Our work reveals that a locus linked to NDDs acts in different striatal circuits, selectively impacting behavior in a sex- and cell type-specific manner, providing new insight into male vulnerability for NDDs.

Development of the Motor Periphery is the Rate-Limiting Step in the Ontogeny of the Vestibulo-ocular Reflex
Sensory deprivation reshapes developing neural circuits, and sensory feedback adjusts the strength of reflexive behaviors throughout life. Sensory development might therefore limit the rate with which behaviors mature, but the complexity of most sensorimotor circuits preclude identifying this fundamental constraint. Here we compared the functional development of components of the vertebrate vestibulo-ocular reflex circuit that stabilizes gaze. We found that vestibular interneuron responses to body tilt sensation developed well before behavioral performance peaked, even without motor neuron-derived feedback. Motor neuron responses developed similarly. Instead, the ontogeny of behavior matched the rate of neuromuscular junction development. When sensation was delayed until after the neuromuscular junction developed, behavioral performance was immediately strong. The matching timecourse and ability to determine behavior establish the development of the neuromuscular junction, and not sensory-derived information, as the rate-limiting process for an ancient and evolutionarily-conserved neural circuit.