bioRxiv Subject Collection: Neuroscience's Journal

Planning and movement activities co-adapt in a motor-reference frame during 3D BCI-controlled reach adaptation in monkey frontal and parietal cortices
Perturbing visual feedback is a powerful tool for studying visuomotor adaptation. However, unperturbed proprioceptive signals in common paradigms inherently co-varies with physical movements and causes incongruency with the visual input. This can create challenges when interpreting underlying neurophysiological mechanisms. We employed a brain-computer interface (BCI) in rhesus monkeys to investigate spatial encoding in frontal and parietal areas during a 3D visuomotor rotation task where only visual feedback was movement-contingent. We found that both brain regions better reflected the adapted motor commands than the perturbed visual feedback during movement preparation and execution. This adaptive response was observed in both local and remote neurons, even when they did not directly contribute to the BCI input signals. The transfer of adaptive changes in planning activity to corresponding movement corrections was stronger in the frontal than in the parietal cortex. Our results suggest an integrated large-scale visuomotor adaptation mechanism in a motor-reference frame spanning across frontoparietal cortices.

Two ways to learn in visuomotor adaptation
Previous research has demonstrated significant inter-individual variability in the recruitment of the fast-explicit and slow-implicit processes during motor adaptation. In addition, we previously identified qualitative individual differences in adaptation linked to the formation and updating of new memory processes. Here, we investigated quantitative and qualitative differences in visuomotor adaptation with a design incorporating repeated learning and forgetting blocks, allowing for precise estimation of individual learning and forgetting rates in fast-slow adaptation models. Participants engaged in a two-day online visuomotor adaptation task. They first adapted to a 30-degree perturbation to eight targets in three blocks separated by short blocks of no feedback trials. Approximately 24 hours later, they performed a no-feedback retention block and a relearning block. We clustered the participants into strong and weak learners based on adaptation levels at the end of day one and fitted a fast-slow system to the adaptation data. Strong learners exhibited a negative correlation between the estimated slow and fast processes, which predicted 24-hour retention and savings, respectively, supporting the engagement of a fast-slow system. The pronounced individual differences in the recruitment of the two processes were attributed to wide ranges of estimated learning rates. Conversely, weak learners exhibited a positive correlation between the two estimated processes, as well as retention but no savings, supporting the engagement of a single slow system. Finally, both during baseline and adaptation, reaction times were shorter for weak learners. Our findings thus revealed two distinct ways to learn in visuomotor adaptation and highlight the necessity of considering both quantitative and qualitative individual differences in studies of motor learning.

Dampened α7 nAChR activity contributes to audiogenic seizures and hyperactivity in a mouse model of Fragile X Syndrome
Fragile X Syndrome (FXS) is the most common form of inherited intellectual disability and often accompanied with debilitating pathologies including seizures and hyperactivity. FXS arises from a trinucleotide repeat expansion in the 5' UTR of the FMR1 gene that silences expression of the RNA-binding protein FMRP. Despite progress in understanding FMRP functions, the identification of effective therapeutic targets has lagged and at present there are no viable treatment options. Here we identify the 7 nicotinic acetylcholine receptor (nAChR) as candidate target for intervention in FXS. In the early postnatal hippocampus of Fmr1 knockout (KO) mice, an established pre-clinical model of FXS, the 7 nAChR accessory protein Ly6H is abnormally enriched at the neuronal surface and mislocalized in dendrites. Ly6H, a GPI-anchored protein, binds 7 nAChRs with high affinity and can limit 7 nAChR surface expression and signaling. We find that 7 nAChR-evoked Ca2+ responses are dampened in immature Glutamatergic and GABAergic Fmr1KO neurons compared to wild type. Knockdown of endogenous Ly6H in Fmr1KO neurons is sufficient to rescue dampened 7 nAChR Ca2+ responses in vitro, providing evidence of a cell-autonomous role for Ly6H aberrant expression in 7 nAChR hypofunction. In line with intrinsic deficits in 7 nAChR activity in Fmr1KO neurons, in vivo administration of the 7 nAChR-selective positive allosteric modulator PNU-120596 reduced hyperactivity and seizure severity in adolescent Fmr1KO mice. Our mechanistic studies together with evidence of the in vivo efficacy of 7 nAChR augmentation implicate 7 nAChR hypofunction in FXS pathology.

Investigate c-Fos changes in genetically identified amygdala neurons after mild footshock stress
The amygdala is a key brain region that processes stress-related inputs to reshape future behaviors. The lateral amygdala (LA), basolateral amygdala (BLA), and central amygdala (CeA) are important subregions that mediate different aspects of stress experiences from receiving sensory input to memory formation and behavioral responding. The principal neurons in these regions are glutamatergic pyramidal neurons, which are genetically separable into two subpopulations, protein phosphatase 1 regulatory subunit 1B-positive (Ppp1r1b, also known as DARPP-32) parvocellular neurons and R-spondin2-positive (Rspo2) magnocellular neurons. Recent studies show that these two subpopulations of amygdala neurons differentially regulate appetitive versus aversive behaviors. The research goal of this study is to explore whether amygdala Ppp1r1b and Rspo2 neurons are transcriptionally activated by moderate stress experience, such that persistent cellular changes are made to influence future functional output of these two subtypes of neurons. To test transcriptional activation, we focused on c-Fos, one of the early genes that are transiently expressed in response to cellular stimulations to regulate downstream gene transcription. Moderate stress was introduced through brief footshocks, with mice without footshock as controls. Between shocked and control mice, we observed similar numbers of Ppp1r1b or Rspo2 neurons per unit area that expressed c-Fos, which was consistent across LA-BLA and CeA. Moreover, in LA-BLA, Ppp1r1b/c-Fos cells consistently outnumber Rspo2/c-Fos cells across treatment conditions, and the reverse is true in CeA. These results suggest that moderate stress experience is not sufficient to induce robust transcriptional alterations in the two key subpopulations of amygdala neurons, and Ppp1r1b versus Rspo2 neuron activities, as measured by c-Fos expression levels, show differential dominance in amygdala subregions.

Constitutive expression of CX3CR1-BAC-Cre introduces minimal off-target effects in microglia
CX3CR1-Cre mouse lines have produced important advancements in our understanding of microglial biology. Recent studies have demonstrated the adverse effects of tamoxifen-induced CX3CR1-Cre expression during development, which include changes in microglial density, phenotype, and DNA damage, as well as anxiety-like behavior. However, the unintended effects of constitutive CX3CR1-BAC-Cre expression remain unexplored. Here, we characterized the effects of CX3CR1-BAC-Cre expression on microglia in CX3CR1-BAC-Cre+/- and CX3CR1-BAC-Cre-/- male and female littermates during early postnatal development and adulthood in multiple brain regions. Additionally, we performed anxiety-like behavior tests to assess changes caused by Cre expression. We found that CX3CR1-BAC-Cre expression causes subtle region-and sex-specific changes in microglial density, volume, and morphology during development, but these changes normalized by adulthood in all brain regions except the hippocampus. No behavioral effects were found. Our findings suggest that the constitutive-Cre model might be less detrimental than the inducible model, and highlight the need for proper controls.

Impact of prenatal delta-9-tetrahydrocannabinol exposure on mouse brain development: a fetal-to-adulthood magnetic resonance imaging study
While cannabis use during pregnancy is often perceived as harmless, little is known about its consequences on offspring neurodevelopment. There is an urgent need to map the effects of prenatal cannabis exposure on the brain through the course of the lifespan. We used magnetic resonance imaging spanning nine timepoints, behavioral assays, and electron microscopy to build a trajectory from gestation to adulthood in mice exposed prenatally to delta-9-tetrahydrocannabinol (THC). Our results demonstrate a spatio-temporal patterning, with ventriculomegaly in THC-exposed embryos followed by a deceleration of brain growth in neonates that is sustained until adulthood, especially in females. We observed consistently impacted regions in both the cortex and subcortex, aligned with sex-dependent changes to social behavior in neonates and increased anxiety-like behavior in adolescents. Our results suggest prenatal THC exposure has a sustained sex-dependent impact on neurodevelopment that may persist into early adulthood.

Sleep Disruption Improves Performance in Simple Olfactory and Visual Decision-Making Tasks
Sleep disruption drastically impacts cognitive functions including decision-making and attention across many different species. In this study, we leveraged the small size and conserved vertebrate brain structure of larval zebrafish to investigate how sleep disruption modulates visual- and olfactory-decision-making. Strikingly, sleep disruption improved performance in both paradigms. Specifically, sleep disruption lengthens reaction times and increases correct decisions in a visual motion discrimination task, an effect that we attribute to longer integration periods in disrupted animals. Using a drift diffusion model, we predict specific circuit changes underlying these effects. Additionally, we demonstrate that sleep disruption heightens odor sensitivity in an olfactory decision-making task, likely mediated by cortisol. Our findings lay essential groundwork for investigating the brain circuit changes that arise from sleep disruption across species.

The role of REM sleep in neural differentiation of memories in the hippocampus
When faced with a familiar situation, we can use memory to make predictions about what will happen next. If such predictions turn out to be erroneous, the brain can adapt by differentiating the representations of the cues that generated the prediction from the mispredicted item itself, reducing the likelihood of future prediction errors. Prior work by Kim et al. (2017) found that violating a sequential association in a statistical learning paradigm triggered differentiation of the neural representations of the associated items in the hippocampus. Here, we used fMRI to test the preregistered hypothesis that this hippocampal differentiation occurs only when violations are followed by rapid eye movement (REM) sleep. In the morning, participants first learned that some items predict others (e.g., A predicts B) then encountered a violation in which a predicted item (B) failed to appear when expected after its associated item (A); the predicted item later appeared on its own after an unrelated item. Participants were then randomly assigned to one of three conditions: remain awake, take a nap containing non-REM sleep only, or take a nap with both non-REM and REM sleep. While the predicted results were not observed in the preregistered left CA2/3/DG ROI, we did observe evidence for our hypothesis in closely related hippocampal ROIs, uncorrected for multiple comparisons: In right CA2/3/DG, differentiation in the group with REM sleep was greater than in the groups without REM sleep (wake and non-REM nap); this differentiation was item-specific and concentrated in right DG. Differentiation effects were also greater in bilateral DG when the predicted item was more strongly reactivated during the violation. Overall, the results presented here provide initial evidence linking REM sleep to changes in the hippocampal representations of memories in humans.

Policy optimization emerges from noisy representation learning
Nervous systems learn representations of the world and policies to act within it. We present a framework that uses reward-dependent noise to facilitate policy optimization in representation learning networks. These networks balance extracting normative features and task-relevant information to solve tasks. Moreover, their representation changes reproduce several experimentally observed shifts in the neural code during task learning. Our framework presents a biologically plausible mechanism for emergent policy optimization amid evidence that representation learning plays a vital role in governing neural dynamics.

Mild focal cooling selectively impacts computations in dendritic trees
Focal cooling is a powerful technique to temporally scale neural dynamics. However, the underlying cellular mechanisms causing this scaling remain unresolved. Here, using targeted focal cooling (with a spatial resolution of 100 micrometers), dual somato-dendritic patch clamp recordings, two-photon calcium imaging, transmitter uncaging, and modeling we reveal that a 5 deg C drop can enhance synaptic transmission, plasticity, and input-output transformations in the distal apical tuft, but not in the basal dendrites of intrinsically bursting L5 pyramidal neurons. This enhancement depends on N-methyl-D-aspartate (NMDA) and Kv4.2, suggesting electrical structure modulation. Paradoxically, and despite the increase in tuft excitability, we observe a reduced rate of recovery from inactivation for apical Na+ channels, thereby regulating back-propagating action potential invasion, coincidence detection, and overall burst probability, resulting in an apparent slowing of somatic spike output. Our findings reveal a differential temperature sensitivity along the basal-tuft axis of L5 neurons analog modulates cortical output.

Computational modelling shows evidence in support of both sensory and frontal theories of consciousness
The role of the prefrontal cortex (PFC) in consciousness is hotly debated. Frontal theories argue that the PFC is necessary for consciousness, while sensory theories propose that consciousness arises from recurrent activity in the posterior cortex alone, with activity in the PFC resulting from the mere act of reporting. To resolve this dispute, we re-analysed an EEG dataset of 30 participants from a no-report inattentional blindness paradigm where faces are (un)consciously perceived. Dynamic causal modelling was used to estimate the effective connectivity between the key contended brain regions, the prefrontal and the posterior cortices. Then, a second-level parametric empirical Bayesian model was conducted to determine how connectivity was modulated by awareness and task-relevance. While an initial data-driven search could not corroborate neither sensory nor frontal theories of consciousness, a more directed hypothesis-driven analysis revealed strong evidence that both theories could explain the data, with a very slight preference for frontal theories. Specifically, a model with backward connections switched off within the posterior cortex explained awareness better (53%) than a model without backward connections from the PFC to sensory regions. Our findings provide some support for a subtle, yet crucial, contribution of the frontal cortex in consciousness, and highlight the need to revise current theories of consciousness.

On the neural substrates of mind wandering and dynamic thought: A drug and brain stimulation study
The impact of mind wandering on our daily lives ranges from diminishing productivity, to facilitating creativity and problem solving. There is evidence that distinct internal thought types can be modulated by transcranial direct current stimulation (tDCS), although little is known about optimal stimulation parameters or the mechanisms behind such effects. In addition, recent findings suggest changes in dopamine availability may alter the effect tDCS has on neural and behavioural outcomes. Dopaminergic functioning has also been implicated in executive processes anticorrelated with mind wandering such as attention and working memory, however the neurochemical mechanisms involved in internal thoughts are largely unknown. Here, we investigated the role of dopamine, and tDCS, on internal thought processes. Specifically, using an attentional control task, we tested whether dopamine availability (levodopa or placebo) mediated the effects of online high definition tDCS (HD-tDCS; 2mA, or sham). There was no evidence for our hypothesised effect of left prefrontal cortex HD-tDCS reducing task unrelated thought, nor freely moving thought. This failure to replicate previous HD-tDCS findings emphasises the importance of employing robust methodological practices within this field to improve confidence in the findings. However, we did find that levodopa reduced freely moving thought, relative to placebo. We also found preliminary evidence that dopamine availability may moderate the relationship between stimulation and behavioural variability performance during periods of task unrelated thought. Overall, these findings suggest that stimulation does not affect dynamic internal thought, however there is initial evidence for the potential effectiveness of targeting the dopaminergic system to reduce spontaneous internal thoughts and improve behavioural performance.

Neuron-astrocyte Coupling in Lateral Habenula Mediates Depressive-like Behaviors
The lateral habenular (LHb) neurons and astrocytes have been strongly implicated in depression etiology but it was not clear how the two dynamically interact during depression onset. Here, using multi-brain-region calcium photometry recording in freely-moving mice, we discover that stress induces a unique, bimodal neuronal response and a most rapid astrocytic response in the LHb. LHb astrocytic calcium requires the 1A-adrenergic receptor, and depends on a recurrent neural network between the LHb and locus coeruleus (LC). Through the gliotransmitter glutamate and ATP/Adenosine, LHb astrocytes mediate the second-wave activation of local LHb neurons as well as release of norepinephrine (NE). Activation or inhibition LHb astrocytic calcium signaling facilitates or prevents stress-induced depressive-like behaviors respectively. These results identify a stress-induced positive feedback loop in the LHb-LC axis, with astrocytes being a critical signaling relay. The identification of this prominent neuron-glia interaction may shed light on stress management and depression prevention.

Cilia dysfunction in the lateral ventricles after neonatal intraventricular hemorrhage does not lead to functional changes in cilia-based CSF flow networks
Intraventricular hemorrhage (IVH) has long been thought to lead to motile cilia dysfunction whereby intraventricular blood breakdown products damage and slough cilia from the ependymal wall. However, specifically how IVH may affect cilia development, structure, and transcriptional activation is not well-understood. Moreover, the impact of blood breakdown product-mediated cilia damage on the functional organization of cilia-based CSF flow networks is unknown. Here, we show hemoglobin exposure affects the number of ciliated ependymal cells in the lateral ventricle (LV) but does not impact in vitro beat frequency of the remaining cilia. Ultrastructurally, IVH decreases the total number of ciliary tufts without impacting axoneme structure. IVH does not result in changes in the expression of cilia-related genes and instead leads to downregulation of neurogenesis markers in parallel with innate immune upregulation. Functionally, we identify three previously uncharacterized cilia-mediated CSF flow domains in the LV lateral wall and show that IVH does not result in widespread disruption of their functional organization. These data de-emphasize cilia as a major contributor to global CSF dysfunction after IVH, and instead call attention to preserving the neurodevelopmental environment and preventing runaway innate immune system activation, as considerations to developing treatment strategies to prevent posthemorrhagic hydrocephalus and other neurodevelopmental sequelae.

A Bidirectional Brain-Fat Body Axis for Pathogen Avoidance
Ingesting pathogens through spoiled food can cause serious harm, including infections, tissue damage, and even death. To prevent these outcomes, many animals have evolved behaviors to avoid consuming harmful pathogens. While pathogen avoidance behavior is conserved across species, the mechanisms linking immune responses of the body with neuron-controlled behavior remain unclear. Building on our previous findings, we here present a new bidirectional body-brain communication between the fat body and the nervous system that drives immune receptor-induced avoidance behavior. We show that immune receptor signaling and a specific antimicrobial peptide (AMP) are essential in both octopaminergic neuromodulatory neurons and the fat body for rapidly reducing pathogen intake after initial ingestion. Mechanistically, the octopaminergic neurons innervate the fly fat body where they trigger a calcium response through a specific octopamine receptor. This octopaminergic signal prompts the fat body to release dopamine. In turn, Dop1R1 signaling in output neurons of the mushroom body, the insect higher brain center, drives pathogen avoidance. Together, our data suggest that ingested pathogens are detected by immune receptors in neurons, which, through synaptic connections, trigger the release of dopamine and AMPs from fat cells. While AMPs combat the pathogens, dopamine reduces further ingestion by inducing behavioral changes. This mechanism demonstrates efficient communication between the body and brain, coordinating survival behaviors through systemic dopamine signaling from the fat body to the brain.

Pyramidal cell types and 5-HT2A receptors are essential for psilocybin's lasting drug action
Psilocybin is a serotonergic psychedelic with therapeutic potential for treating mental illnesses. At the cellular level, psychedelics induce structural neural plasticity, exemplified by the drug-evoked growth and remodeling of dendritic spines in cortical pyramidal cells. A key question is how these cellular modifications map onto cell type-specific circuits to produce psychedelics' behavioral actions. Here, we use in vivo optical imaging, chemogenetic perturbation, and cell type-specific electrophysiology to investigate the impact of psilocybin on the two main types of pyramidal cells in the mouse medial frontal cortex. We find that a single dose of psilocybin increased the density of dendritic spines in both the subcortical-projecting, pyramidal tract (PT) and intratelencephalic (IT) cell types. Behaviorally, silencing the PT neurons eliminates psilocybin's ability to ameliorate stress-related phenotypes, whereas silencing IT neurons has no detectable effect. In PT neurons only, psilocybin boosts synaptic calcium transients and elevates firing rates acutely after administration. Targeted knockout of 5-HT2A receptors abolishes psilocybin's effects on stress-related behavior and structural plasticity. Collectively these results identify a pyramidal cell type and the 5-HT2A receptor in the medial frontal cortex as playing essential roles for psilocybin's long-term drug action.

Synchronous activation of striatal cholinergic interneurons induces local serotonin release
Striatal cholinergic interneurons (CINs) activate nicotinic acetylcholine receptors (nAChRs) on dopamine axons to extend the range of dopamine release. Here we show that synchronous activation of CINs induces and extends the range of local serotonin release via a similar mechanism. This process is exaggerated in the hypercholinergic striatum of a mouse model of OCD-like behavior, implicating CINs as critical regulators of serotonin levels in the healthy and pathological striatum.

Synaptic and Somatic Targeting of ArcLight, a Genetically Encoded Voltage Indicator
Voltage signals in neurons are highly compartmentalized, which can influence their specific functions within neuronal circuits. Targeting of a genetically encoded voltage indicator (GEVI) to specific subcellular compartments can enhance the signal-to-noise ratio and provide more precise information about the location and timing of synaptic firing across different neuronal regions, reducing spatiotemporal signal convolution. To achieve subcellular targeting of the GEVI, ArcLight, we utilized five different postsynaptic targeting sequences (Shaker K+ channel C-terminus, stargazin C-terminus, rat Neuroligin-1 C-terminus, and anti-homer1 nanobodies HC20 & HC87) to direct ArcLight expression to the excitatory postsynaptic density. Additionally, we assessed a presynaptic-targeting tag (rat Neurexin-1{beta} C-terminus) and a somatodendritic targeting tag (Kv2.1-Lk-Tlcn C-terminus). Patch clamp experiments in HEK293 cells showed that the targeting tags used in this study did not significantly alter ArcLight's voltage sensitivity compared to controls. AAV infection in the mouse olfactory bulb demonstrated that the subcellular targeting sequences effectively localized GEVI expression to specific compartments of mitral/tufted cells, including postsynaptic densities, presynaptic terminals, and somatodendritic regions. Furthermore, in vivo voltage imaging in mice expressing targeting-enhanced ArcLight variants revealed odorant-evoked responses similar to those observed with the original ArcLight. This indicates that subcellular targeting did not significantly impact the voltage sensing capability of ArcLight in mitral/tufted cells.

An exploration of complex action stopping across multiple datasets: Insights into the mechanisms of action cancellation and re-programming
A long history of psychological experiments has utilised stop signal paradigms to assess action inhibition. Recent studies have investigated complex stopping behaviours, such as response-selective stopping where only one component of a bimanual action requires cancellation. A current emphasis has been to utilise electromyographical (EMG) recordings to assess the temporal dynamics of action inhibition at the level of the muscle, beyond those based solely on observable behavioural events. Here, we combine EMG and behavioural data from 17 cohorts of healthy younger and older adults yielding over 42,000 response-selective stopping trials, providing unique insights into this emerging field. Expanding from past research in this area, our robust single-trial EMG analyses permit detection of cancelled (partial) and response-generating EMG bursts in both hands, revealing substantial overlaps in the distributions of timing of action cancellation and re-programming. These findings are consistent with recent experimental and modelling evidence, suggesting that response-selective stopping involves two independent processes: a discrete bimanual stop and initiation of a new unimanual response. This overlap appears incompatible with the recent pause-then-cancel model, and more consistent with a broader 'pause-then-retune' account, where a slower process mediates any action updating, not just cancellation. Moreover, this independence means that cancellation can happen at any time during motor planning and execution, against the notion of an observable 'point of no return' in motor actions. We also discuss best practices for the analysis of EMG data and indicate how methodological aspects, such as choosing appropriate reference time points, can influence the outcomes and their interpretation.

Tachykinin1-expressing neurons in the parasubthalamic nucleus control active avoidance learning
Active avoidance is a type of instrumental behavior that requires an organism actively to engage in specific actions to avoid or escape from a potentially aversive stimulus and is crucial for the survival and well-being of organisms. It requires a widely distributed, hard-wired neural circuits spanning multiple brain regions, including the amygdala and thalamus. However, less is known about whether and how the hypothalamus encodes and controls active avoidance learning. Here we identify a previously unknown role for the parasubthalamic nucleus (PSTN), located in the lateral subdivision of the posterior hypothalamus, in the encoding and control of active avoidance learning. Fiber photometry calcium imaging shows that the activity of tachykinin1-expressing PSTN (PSTNTac1) neurons progressively increases during this learning. Cell-type specific ablation and optogenetic inhibition of PSTNTac1 neurons attenuates active avoidance learning, whereas optogenetic activation of these cells promotes this learning via a negative motivational drive. Moreover, the PSTN mediates this learning differentially through its downstream targets. Together, this study identifies the PSTN as a new member of the neural networks involved in active avoidance learning and offers us potential implications for therapeutic interventions targeting anxiety disorders and other conditions involving maladaptive avoidance learning.

Robustness in Hopfield neural networks with biased memory patterns
Biological neural networks are able to store and retrieve patterns in the presence of different types of noise. Hopfield neural networks have been inspired by biological neural networks and provide a model for auto-associative memory patterns. An important parameter in these networks is the pattern bias, i.e. the mean activity level of the network, which is closely related to the degree of sparseness in the coding scheme. Here we studied the relation between robustness against different types of biologically-motivated noise and pattern bias. To do so, we developed performance and robustness measures, which are applicable to varying degrees of sparseness of the memory representations, using analytically-optimized thresholds and corruption tolerances adjusted by mutual information. We then applied these tools in numerical simulations and found that, for different types of noise, the pattern load, i.e. the number of patterns that the network has to store, determined which pattern bias is most robust. Across different types of noise, the higher the pattern load was, the more biased was the most robust performing pattern representation. Given the variation in the sparseness level in different brain regions, our findings suggest that memory pattern encoding schemes (i.e. degree of sparseness) in different brain regions might be adapted to the expected memory load in order to best mitigate the adverse effects of disruptions.

Endocytosis restricts synapse growth by attenuating Highwire/PHR1-dependent JNK signaling in a pathway parallel to the BMP signaling
Endocytosis regulates the retrieval of synaptic membranes and the trafficking of growth signaling receptors. While Drosophila endocytic mutants show synaptic overgrowth at the neuromuscular junctions (NMJs), the signaling pathways by which endocytosis restricts synapse growth remain poorly understood. Here, we demonstrate that sigma2-adaptin, one of the obligate subunits of the AP2 complex, facilitates the degradation and trafficking of E3-ubiquitin ligase Highwire (Hiw)/PHR1 and inhibits the c-Jun N-terminal kinase (JNK) signaling. This function of sigma2-adaptin is independent of its Bone Morphogenetic Protein (BMP) signaling regulation. Loss of sigma2-adaptin leads to Hiw accumulation and mislocalization in the neuronal cell body, leading to elevated MAP3K Wallenda levels. Stabilizing Hiw by expressing Rae1 or genetically blocking the JNK signaling suppresses the synaptic overgrowth defects observed in sigma2-adaptin mutants. Remarkably, blocking BMP and JNK signaling pathways suppressed the synaptic overgrowth observed in the sigma2-adaptin mutant to the wild-type levels. Finally, we show that loss of Rab11 but not Rab5 or Rab7 leads to accumulation/mislocalization of Hiw in the neuronal cell body akin to sigma2-adaptin mutants. We propose a model in which endocytosis regulates Rab11-mediated Hiw trafficking and attenuates JNK signaling in a pathway parallel to the BMP signaling to restrict synaptic growth.

Meta-atlas of Juvenile and Adult Enteric Neuron scRNA-seq for Dataset Comparisons and Consensus on Transcriptomic Definitions of Enteric Neuron Subtypes
Background The enteric nervous system (ENS) is a complex network of interconnected ganglia within the gastrointestinal (GI) tract. Among its diverse functions, the ENS detects bowel luminal contents and coordinates the passing of stool. ENS defects predispose to GI motility disorders. Previously, distinct enteric neuron types were cataloged by dye-filling techniques, immunohistochemistry, retrograde labeling, and electrophysiology. Recent technical advances in single cell RNA-sequencing (scRNA-seq) have enabled transcriptional profiling of hundreds to millions of individual cells from the intestine. These data allow cell types to be resolved and compared to using their transcriptional profiles (clusters) rather than relying on antibody labeling. As a result, greater diversity of enteric neuron types has been appreciated. Because each scRNA-seq study has relied on different methods for cell isolation and library generation, numbers of neuron clusters and cell types detected differs between analyses. Cell counts in each dataset are particularly important for characterization of rare cell types since small numbers of profiled cells may not sample rare cell types. Importantly, each dataset, depending on the isolation methods, may contain different proportions of cells that are not detected in other datasets. Aggregation of datasets can effectively increase the total number of cells being analyzed and can be helpful for confirming the presence of low-abundance neuron types that might be absent or observed infrequently in any single dataset. Results Here we briefly systematically review each Mus musculus single cell or single nucleus RNA-sequencing enteric nervous system dataset. We then reprocess and computationally integrate these select independent scRNA-seq enteric neuron datasets with the aim to identify new cell types, shared marker genes across juvenile to adult ages, dataset differences, and achieve some consensus on transcriptomic definitions of enteric neuronal subtypes. Conclusions Data aggregation generates a consensus view of enteric neuron types and improves resolution of rare neuron classes. This meta-atlas offers a deeper understanding of enteric neuron diversity and may prove useful to investigators aiming to define alterations among enteric neurons in disease states. Future studies face the challenge of connecting these deep transcriptional profiles for enteric neurons with historical classification systems.

Intelligence and Cognitive Flexibility Selectively Modulate Working Memory Functioning
Working memory is a key component of intelligence, which can be underpinned by task connectome, while cognitive flexibility plays a role in adaptive and executive function that supports working memory processes. However, it remains unknown how intelligence and cognitive flexibility modulate working memory functioning, in terms of behavioural performance and task-related brain hierarchy. Current study investigated the working memory task-related behaviour and brain connectomic gradient in healthy adults together with their intelligence and cognitive flexibility measures. Results showed cognitive flexibility and intelligence were not significantly correlated with each other but with working memory function. Principal component and partial least square analysis revealed that nearly half of variance was explained by their overlap component, which linked with task gradient values of frontoparietal and ventral attention network representing executive, control and cognitive functioning. Individuals with higher intelligence and cognitive flexibility showed less distance between frontoparietal/ventral attention network and unimodal regions in gradient axis during working memory performance. Further analyses demonstrated that task gradient of frontoparietal and ventral attention network was significantly associated with working memory function, and selectively mediated by cognitive flexibility and intelligence, which may suggest partly convergent neural mechanisms for higher order functions that are involved in working memory functioning. In conclusion, current study provides new insight into the relationship among task connectomic gradient, working memory, intelligence, and cognitive flexibility, which helps understand the multi-component model of working memory and underlying task gradient principle.

Normalized Dynamic Time Warping Increases Sensitivity In Differentiating Functional Network Connectivity In Schizophrenia
Our study advances the application of dynamic time warping (DTW) as a functional connectivity measure by introducing a normalization technique which enhances the detection of schizophrenia effects in comparison to both standard DTW and traditional correlation methods. By rigorously examining the statistical validity of DTW and our proposed normalized DTW measure, we show that it effectively captures interdependencies between fMRI signals beyond linear correlation, offering a more robust, complementary and informative approach to functional connectivity analysis. Through comprehensive evaluations, we demonstrate that normalized DTW is more sensitive to differences in functional brain network connections between schizophrenia and controls, highlighting its potential to provide deeper insights into clinical research.

Association between loneliness and hippocampal responses to dynamic social stimuli in psychotic disorders
Background: The incidence of loneliness has increased over the past several decades worldwide and is particularly common among people with serious mental illnesses. However, this public health problem has been difficult to address, in part because the neurocognitive mechanisms underlying loneliness are poorly understood. Methods: To investigate these mechanisms, a functional magnetic resonance imaging (fMRI) study was conducted which accounted for known cognitive biases associated with loneliness. Participants with (n = 40) and without (n = 60) psychotic disorders (PD) viewed images of faces that appeared to approach or withdraw from the participants, while fMRI data were collected. Following the scanning, participants rated the trustworthiness of the faces, and these ratings were included as weights in the fMRI analyses. Neural responses to approaching versus withdrawing faces were measured, and whole brain regression analyses, with loneliness as the regressor, were performed. Results: In the PD and full samples, a higher level of loneliness was significantly associated with greater responses of the hippocampus and areas of the basal ganglia to withdrawing (versus approaching) face stimuli. Moreover, the effects in the hippocampus, but not the basal ganglia, remained significant after controlling for potential confounds such as social activity levels, depression and social anhedonia. Lastly, in a subset of the sample (n = 66), greater hippocampal responses to withdrawing faces predicted greater loneliness one year later. Conclusions: Heightened responses of the hippocampus to withdrawing faces may represent a candidate objective marker of loneliness that could be modified by interventions targeting loneliness.

Molecular Signatures of Resilience to Alzheimer's Disease in Neocortical Layer 4 Neurons
Single-cell omics is advancing our understanding of selective neuronal vulnerability in Alzheimer's disease (AD), revealing specific subtypes that are either susceptible or resilient to neurodegeneration. Using single-nucleus and spatial transcriptomics to compare neocortical regions affected early (prefrontal cortex and precuneus) or late (primary visual cortex) in AD, we identified a resilient excitatory population in layer 4 of the primary visual cortex expressing RORB, CUX2, and EYA4. Layer 4 neurons in association neocortex also remained relatively preserved as AD progressed and shared overlapping molecular signatures of resilience. Early in the disease, resilient neurons upregulated genes associated with synapse maintenance, synaptic plasticity, calcium homeostasis, and neuroprotective factors, including GRIN2A, RORA, NRXN1, NLGN1, NCAM2, FGF14, NRG3, NEGR1, and CSMD1. We also identified KCNIP4, which encodes a voltage-gated potassium (Kv) channel-interacting protein that interacts with Kv4.2 channels and presenilins, as a key factor linked to resilience. KCNIP4 was consistently upregulated in the early stages of pathology. Furthermore, AAV-mediated overexpression of Kcnip4 in a humanized AD mouse model reduced the expression of the activity-dependent genes Arc and c-Fos, suggesting compensatory mechanisms against neuronal hyperexcitability. Our dataset provides a valuable resource for investigating mechanisms underlying resilience to neurodegeneration.

Visually-guided compensation of deafening-induced song deterioration
Human language learning and maintenance depend primarily on auditory feedback but are also shaped by other sensory modalities. Individuals who become deaf after learning to speak (post-lingual deafness) experience a gradual decline in their language abilities. A similar process occurs in songbirds, where deafness leads to progressive song deterioration. However, songbirds can modify their songs using non-auditory cues, challenging the prevailing assumption that auditory feedback is essential for vocal control. In this study, we investigated whether deafened birds could use visual cues to prevent or limit song deterioration. We developed a new metric for assessing syllable deterioration called the spectrogram divergence score. We then trained deafened birds in a behavioral task where the spectrogram divergence score of a target syllable was computed in real-time, triggering a contingent visual stimulus based on the score. Birds exposed to the contingent visual stimulus - a brief light extinction - showed more stable song syllables than birds that received either no light extinction or randomly triggered light extinction. Notably, this effect was specific to the targeted syllable and did not influence other syllables. This study demonstrates that deafness-induced song deterioration in birds can be partially mitigated with visual cues.