bioRxiv Subject Collection: Neuroscience's Journal

Cross-species brain-wide mapping reveals a conserved and coordinated network engaged by NAc DBS
Nucleus accumbens (NAc) deep brain stimulation (DBS) has been increasingly explored as a treatment modality for refractory neuropsychiatric disorders. Uncovering the accumbens network that is engaged by DBS is a critical step forward in understanding how modulating this important node impacts the broader mesocorticolimbic circuit. Using whole-brain clearing and unbiased, brain-wide neural activity mapping, we found that NAc DBS increases neural activity in a coordinated mesocorticolimbic network in mice. Simultaneous intracranial electrophysiology recordings from the human NAc and brief stimulation epochs of homologous mesocorticolimbic nodes revealed similar connectivity. Altogether, these results identify specific connectivity conserved across species within the mesocorticolimbic circuit that may underlie mechanisms of NAc DBS.

Modeling Attention and Binding in the Brain through Bidirectional Recurrent Gating
Attention is a key component of the visual system, essential for perception, learning, and memory. Attention can also be seen as a solution to the binding problem: concurrent attention to all parts of an entity allows separating it from the rest. However, the rich models of attention in computational neuroscience are generally not scaled to real-world problems and there are thus many behavioral and neural phenomena that current models cannot explain. Here, we propose a bidirectional recurrent model of attention that is inspired by modern neural networks for image segmentation. It conceptualizes recurrent connections as a multi-stage internal gating process where bottom-up connections transmit features, while top-down and lateral connections transmit attentional gating signals. Our model can recognize and segment simple stimuli such as digits as well as objects in natural images and is able to be prompted with object labels, attributes or locations. It can learn to perform a range of behavioral findings, such as object binding, selective attention, inhibition of return, and visual search. It also replicates a variety of neural findings, including increased activity for attended objects, features, and locations, attention-invariant tuning, and relatively late onset attention. Most importantly, our proposed model unifies decades of cognitive and neurophysiological findings of visual attention into a single principled architecture. Our results highlight that the ability to selectively and dynamically focus on specific parts of stimulus streams can help artificial neural networks to better generalize and align with human brains.

Photoreceptor degeneration has heterogeneous effects on functional retinal ganglion cell types
Retinitis pigmentosa is a hereditary disease causing progressive degeneration of rod and cone photoreceptors, with no effective therapies. Using the rd10 mouse model, which mirrors the human condition, we examined its disease progression. Rods deteriorate by postnatal day (P) 45, followed by cone degeneration, with most photoreceptors lost by P180. Until then, retinal ganglion cells (RGCs) remain light-responsive, albeit only under photopic conditions, despite extensive outer retinal remodelling. However, it is still unknown whether the different functional RGC types remain stable, or if some types differentially alter their activity or are even lost during disease progression. Here, we addressed if and how the response diversity of functional RGC types changes with rd10 disease progression. At P30, we were able to identify all functional wild-type RGC types also in rd10 retina, suggesting that at this early degenerative stage, the full breadth of retinal output is still present. Remarkably, we found that the fractions of functional types changed throughout progressing degeneration between rd10 and wild-type: Responses of RGCs with 'Off'-components ('Off' and 'On-Off' RGCs) seemed to be more vulnerable than 'On'-cells, with 'Fast-On' types being the most resilient. Notably, direction-selective RGCs appeared to be more vulnerable than orientation-selective RGCs. In summary, we found differences in resilience of response types (from resilient to vulnerable): 'Uncertain' > 'Fast On' > 'Slow On' > 'On-Off' > 'Off'. Taken together, our results suggest that rd10 photoreceptor degeneration has heterogeneous effects on functional RGC types, with distinct sets of types losing their characteristic light responses earlier than others. This differential susceptibility of RGC circuits may be of relevance for future neuroprotective therapeutic strategies.

A three-dimensional immunofluorescence atlas of the brain of the hackled-orb weaver spider, Uloborus diversus.
Spider orb-web building is a captivating, rare example of animal construction, whose neural underpinnings remain undiscovered. An essential step in understanding the basis of this behavior is a foundational mapping of the spider's neuroanatomy, which has thus far been primarily studied using non-web building species. We created a three-dimensional atlas for the hackled orb-weaver, Uloborus diversus, based on immunostaining for the presynaptic component, synapsin, in whole-mounted spider synganglia. Aligned to this volume, we examined the expression patterns of neuronal populations representing many of the classical neurotransmitter and neuromodulators, as well as a subset of neuropeptides - detailing immunoreactivity in an unbiased fashion throughout the synganglion, revealing co-expression in known structures, as well as novel neuropils not evident in prior spider works. This optically-sliced, whole-mount atlas is the first of its kind for spiders, representing a substantive addition to knowledge of brain anatomy and neurotransmitter expression patterns for an orb-weaving species.

Bradykinesia and postural instability in a model of prodromal Synucleinopathy with alpha-Synuclein aggregation in the gigantocellular nuclei.
Alpha-Synuclein (aSyn) accumulation within the extra-nigral neuronal populations in brainstem, including the gigantocellular nuclei (GRN/Gi) of reticular formation, is a recognized feature during the prodromal phase of Parkinson disease (PD). Accordingly, there is a burgeoning interest in animal model development for understanding the pathological significance of extra-nigral synucleinopathy, in relation to motor and/or non-motor symptomatology in PD. Here, we report an experimental paradigm for the induction of aSyn aggregation in brainstem, with stereotaxic delivery of pre-formed fibrillar (PFF) aSyn in the pontine GRN of transgenic mice expressing the mutant human Ala53Thr aSyn (M83 line). Our data show that PFF aSyn-induced aggregate pathology in GRN leads to progressive decline in spontaneous locomotion and an early phenotype of postural instability. This early phase of bradykinesia was followed by a moribund stage, characterized by worsening motor performance and impaired survival with substantial aSyn aggregation in several brain regions beyond the GRN. Collectively, our observations suggest an experimental framework for studying the pathological significance of aSyn aggregation in GRN in relation to features of movement disability in PD. With further refinements, we anticipate that this model holds promise as a test-bed for translational research in PD and related disorders.

Use of the non-paretic arm reflects a habitual behaviour in chronic stroke
Background: A proportion of stroke survivors use their affected arm less than might be expected based on their level of impairment. The resulting non-use of the affected arm has a negative impact on participation in neurorehabilitation and functional independence. However, non-use remains poorly understood. One possibility is that prioritising the non-paretic arm reflects a habit, despite residual functional capacity in the paretic arm. Methods: 30 chronic stroke survivors (Mean FM: 28.9 +/- 11.3) participated in a simplified version of the forced response paradigm, which reliably identifies the presence of a habit. Participants were asked to choose which arm to use to maximise points scored during a reaching task. During half of the trials, the presumed habit of using the non-paretic arm yielded more points, whereas in the other half using the non-paretic arm incurred a loss of points. Participants completed two versions of this task, once with unlimited response time available and once without. Results: Participants scored fewer points in the limited response condition compared to the unlimited response conditions. This difference was driven by a selective increase in the use of the non-paretic arm in trials where the paretic arm yielded more points. The results were not mediated by former hand dominance. Conclusions: Our results demonstrate that not using the non-paretic arm may reflect a habit response that is more readily triggered in demanding (e.g. time-limited) situations. This may explain why successful neurorehabilitation does not always result in a more functionally useful arm. Our results pave the way for targeted interventions such as habit breaking techniques to be included in clinical practise.

Three Subtypes Of Autism Spectrum Disorder With Transcriptomic Signatures Derived From Morphometric Similarity Networks
Autism spectrum disorder (ASD) is a prevalent and highly heterogeneous neurodevelopmental disorder. Previous studies have attempted to identify ASD subgroups by analyzing isolated cortical structural features. However, these studies have not considered the relationship between multiple structural features, which provide information on the structural organization of the brain. Morphometric similarity network (MSN), a structural brain network contributed by multiple anatomical features (gray matter volume, mean cortical thickness, surface area, mean curvature, Gaussian curvature, curvature index, and fold index), strongly relates to cytoarchitectonic and genomic measures of histological similarity between cortical areas. We applied K-means clustering on MSN from 236 individuals with ASD and identified three subtypes. Subtype-1 showed relatively similar MSN values with typically developmental individuals (TD). Subtype-2 showed higher morphometric similarities in the lateral frontal and temporal cortical regions and lower in anterior prefrontal and occipital regions compared to TD. These patterns were the opposite in subtype-3. Behaviorally, subtype-3 had more severe verbal and social deficits compared to subtype-2. The weaker resting-state functional connectivity (rs-FC) between the language and salience networks was observed between subtype-2 and TD. Subtype-3 had stronger rs-FC between salience and default mode networks (DMN), between frontoparietal and visual networks, and between language and dorsal attention networks, while weaker rs-FC within DMN, within sensorimotor, and within salience networks. In addition, genes with expression patterns associated with regional MS changes in ASD subtypes were functionally enriched in neuron-specific biological processes related to nervous system development, synaptic signaling and chromatin organization. These genes were particularly enriched in GABAergic neurons, glutamatergic neurons, astrocytes and microglia. Taken together, our findings suggest the existence of different neuroanatomical subtypes based on multiple anatomical features in ASD with distinct transcriptomic signatures and functional connectome patterns.

Mitochondrial complex I deficiency occurs in skeletal muscle of a subgroup of individuals with Parkinson's disease
Widespread neuronal complex I (CI) deficiency was recently reported to be a characteristic in a subgroup of individuals with idiopathic Parkinson's disease (PD). Here, we sought to determine whether a CI deficient subgroup could be discerned using clinically accessible muscle biopsy. Vastus lateralis needle biopsies were collected from 83 individuals with PD and 29 neurologically healthy controls and analyzed by immunohistochemistry for complexes I and IV, cytochrome c oxidase/succinate dehydrogenase (COX/SDH) histochemistry, and spectrophotometric activity assays of complexes I-IV. Mitochondrial DNA (mtDNA) copy number, deletions, and point variation were analyzed in single muscle fibers and bulk biopsy samples. PD muscle exhibited reduced CI activity at the group level, with 9% of cases falling below two standard deviations of the control group. This deficiency was not associated with mtDNA abnormalities. Our findings support the existence of a PD subpopulation characterized by CI pathology and suggest that stratification by extra-neural mitochondrial dysfunction may be informative for selecting individuals for clinical trials.

Ventral tegmental area dopamine neural activity switches simultaneously with rule representations in the prefrontal cortex and hippocampus
Multiple brain regions need to coordinate activity to support cognitive flexibility and behavioral adaptation. Neural activity in both the hippocampus (HPC) and prefrontal cortex (PFC) is known to represent spatial context and is sensitive to reward and rule alterations. Midbrain dopamine (DA) activity is key in reward seeking behavior and learning. There is abundant evidence that midbrain DA modulates HPC and PFC activity. However, it remains underexplored how these networks engage dynamically and coordinate temporally when animals must adjust their behavior according to changing reward contingencies. In particular, is there any relationship between DA reward prediction change during rule switching, and rule representation changes in PFC and CA1? We addressed these questions using simultaneous recording of neuronal population activity from the hippocampal area CA1, PFC and ventral tegmental area (VTA) in male TH-Cre rats performing two spatial working memory tasks with frequent rule switches in blocks of trials. CA1 and PFC ensembles showed rule-specific activity both during maze running and at reward locations, with PFC rule coding more consistent across animals compared to CA1. Optogenetically tagged VTA DA neuron firing activity responded to and predicted reward outcome. We found that the correct prediction in DA emerged gradually over trials after rule-switching in coordination with transitions in PFC and CA1 ensemble representations of the current rule after a rule switch, followed by behavioral adaptation to the correct rule sequence. Therefore, our study demonstrates a crucial temporal coordination between the rule representation in PFC/CA1, the dopamine reward signal and behavioral strategy.

Behavioral state and stimulus strength regulate the role of somatostatin interneurons in stabilizing network activity
Inhibition stabilization enables cortical circuits to encode sensory signals across diverse contexts. Somatostatin-expressing (SST) interneurons are well-suited for this role through their strong recurrent connectivity with excitatory pyramidal cells. We developed a cortical circuit model predicting that SST cells become increasingly important for stabilization as sensory input strengthens. We tested this prediction in mouse primary visual cortex by manipulating excitatory input to SST cells, a key parameter for inhibition stabilization, with a novel cell-type specific pharmacological method to selectively block glutamatergic receptors on SST cells. Consistent with our model predictions, we find antagonizing glutamatergic receptors drives a paradoxical facilitation of SST cells with increasing stimulus contrast. In addition, we find even stronger engagement of SST-dependent stabilization when the mice are aroused. Thus, we reveal that the role of SST cells in cortical processing gradually switches as a function of both input strength and behavioral state.

Early life stress influences epilepsy outcomes in mice
Stress is a common seizure trigger that has been implicated in worsening epilepsy outcomes. The neuroendocrine response to stress is mediated by the hypothalamic-pituitary-adrenal (HPA) axis and HPA axis dysfunction worsens epilepsy outcomes, increasing seizure burden, behavioral comorbidities, and risk for sudden unexpected death in epilepsy (SUDEP) in mice. Early life stress (ELS) reprograms the HPA axis into adulthood, impacting both the basal and stress-induced activity. Thus, we propose that ELS may influence epilepsy outcomes by influencing the function of the HPA axis. To test this hypothesis, we utilized the maternal separation paradigm and examined the impact on seizure susceptibility. We show that ELS exerts a sex dependent effect on seizure susceptibility in response to acute administration of the chemoconvulsant, kainic acid, which is associated with an altered relationship between seizure activity and HPA axis function. To further examine the impact of ELS on epilepsy outcomes, we utilized the intrahippocampal kainic acid model of chronic epilepsy in mice previously exposed to maternal separation. We find that the relationship between corticosterone levels and the extent of epileptiform activity is altered in mice subjected to ELS. We demonstrate that ELS impacts behavioral outcomes associated with chronic epilepsy in a sex-dependent manner, with females being more affected. We also observe reduced mortality (presumed SUDEP) in female mice subjected to ELS, consistent with previous findings suggesting a role for HPA axis dysfunction in SUDEP risk. These data demonstrate for the first time that ELS influences epilepsy outcomes and suggest that previous life experiences may impact the trajectory of epilepsy.

Neurite Density and Free Water in the Gray and White Matter of Early Psychosis Patients
Diffusion weighted imaging has been frequently used to characterize the white matter in patients with schizophrenia, but the most commonly used model, diffusion tensor imaging (DTI), is not specific to the histological nature of microstructural changes. This is particularly true in the more complex grey matter tissue. Furthermore, DTI changes have not been consistently reported in early schizophrenia populations, but this does not exclude more subtle changes that may not affect the model fit. Recently developed biophysical models of diffusion, such as the neurite orientation dispersion and density imaging (NODDI) model, may overcome these issues by quantifying specific tissue subcompartments, capturing diffusion profiles characteristic of intra-neurite, extra-neurite, and free water space. We applied the NODDI model to early schizophrenia patients (n=54) and healthy controls (n=51) from the Human Connectome Project - Early Psychosis dataset, investigating both the grey and white matter. We observed a diffuse, increased free water fraction throughout the grey matter, especially in the left insula, though there were not notable changes in the white matter. The spatial variation in the grey matter free water was not fully explained by the partial volume effects from the cerebrospinal fluid, indicating a role for tissue edema. The role of vasogenic processes in early stages of psychosis that may precede white matter anomalies documented in later disease stages warrant further investigation.

Non-allometric expansion and enhanced compartmentalization of Purkinje cell dendrites in the human cerebellum
Purkinje cell (PC) dendrites are optimized to integrate the vast cerebellar input array and drive the sole cortical output. Classically, PCs are stereotypical computational units. Yet, mouse PCs are morphologically diverse and those with multi-dendritic structure can receive non-canonical climbing fiber (CF) multi-innervation that confers independent compartment-specific signaling. This morphological motif is universal among human PCs, but their morphology is otherwise uncharacterized. Do human PCs exceed allometry to achieve enhanced integrative capacities relative to mouse? To answer this, we used comparative histology in human and mouse to analyze cellular morphology, parallel fiber (PF) and CF input arrangement, and regional PC demographics. Quantitatively and qualitatively distinct, human PCs: are substantially larger than predicted by cortical thickness, have increased spine density and size, commonly host multiple CFs, and exhibit previously unreported "spine clusters". They harness a horizontally oriented multi-dendritic motif to multiplex broad PF/CF arrays, which may subserve computations requiring multi-modal association.

An embodied perspective: angular gyrus and precuneus decode selfhood in memories of naturalistic events
While memory encoding is often assumed to occur from an in-body (first-person) perspective, out-of-body experiences demonstrate that we can form memories from a third-person perspective. This phenomenon offers a unique opportunity to investigate how embodiment interacts with visual perspective during encoding to shape how past events are recalled. Participants formed memories for naturalistic events following a manipulation of their sense of embodiment from in-body and out-of-body perspectives and recalled them during functional scanning. Region of interest multivariate analyses examined how the angular gyrus, precuneus, and hippocampus reflected visual perspective, embodiment, and their interaction during remembering. Patterns of activity during retrieval in the left angular gyrus and bilateral precuneus predicted the combination of embodiment and visual perspective, and embodiment on its own separated from visual perspective. Decoding accuracy was not significant for any region when predicting visual perspective alone. Our results suggest that the involvement of posterior parietal regions in establishing visual perspectives within memories cannot be disentangled from embodiment. Encoding events from an embodied in-body perspective led to higher memory accuracy following repeated retrieval. These results elucidate how fundamental feelings of being located within and experiencing the world from the perspective of one's own body are integrated within memory.

Developmental progression of prefrontal circuit dysfunction in a Shank3-/- mouse model of autism spectrum disorder
Autism Spectrum Disorders (ASD) are a group of neurodevelopmental disorders with heterogeneous causes, characterized by communication deficits, impaired social interactions, and repetitive behaviors. Despite numerous studies focused on pathophysiological circuit mechanisms of ASD in mature mice, little is known regarding ASD onset and its evolution through development in these models. To explore early disruptions in mPFC development, we utilized the Shank3 knockout (Shank3-/-) mouse model, a well-established genetic model of ASD. The medial prefrontal cortex (mPFC) is crucial for higher-order cognitive functions and social behavior, making it a key brain area of interest for understanding ASD pathology. SHANK3 is crucial for glutamatergic synapse maturation, and the Shank3-/- mouse has been well-characterized for displaying ASD-related behavioral phenotypes. We investigated network, cellular, and synaptic changes in the mPFC at two developmental stages, P14 and adulthood (>P55). Our findings revealed that while differences in neuronal excitability including hypofunction are detectable at P14, global mPFC dysfunction, including network hyperfunction and layer 5 pyramidal cell hyperexcitability, only becomes evident in adulthood. This suggests that early cellular changes that precede the development of behavioral deficits may lead to compensatory mechanisms that contribute to more pronounced mPFC deficits later in development. These results highlight the complex and evolving nature of mPFC dysfunction in ASD and suggest that early synaptic changes may set the stage for later behavioral and cognitive deficits.

Ketogenic interventions restore cognition and modulate peripheral metabolic dysfunctions in Alzheimer's disease mouse models
Lifestyle factors modulate dementia risk. We investigated mechanisms of dementia risk reduction by emerging dietary ketogenic interventions. We show that distinct interventions, a medium-chain triglycerides (MCT)-enriched diet and a carbohydrate-free, high-fat diet (CFHF), improve cognition and dendritic spine density of memory-associated hippocampal neurons in two mouse models of Alzheimer disease (AD). Only the CFHF diet drove increased circulating ketones, suggesting distinct underlying mechanisms. AD mice exhibited baseline and diet-induced susceptibility to peripheral metabolic disturbances that were improved by MCT and exacerbated by CFHF diets. Prominent AD-associated dysregulation of the liver transcriptome was largely restored by both interventions, but MCT also downregulated lipogenic enzymes and did not trigger a CFHF-like inflammatory signature. Novel AD- and diet-induced plasmatic changes in hormones and lipid species were identified. Thus, different ketogenic interventions yield cognitive benefits in AD models while showing intervention-specific modulation of peripheral metabolic defects, with implications for design of therapeutic ketogenic strategies.

Unravelling the impact of TLR4 and sex on chronic alcohol consumption-induced lipidome dysregulation in extracellular vesicles
The lipids that form extracellular vesicles (EVs) play critical structural and regulatory roles, and cutting-edge bioinformatics strategies have shown the ability to decipher lipid metabolism and related molecular mechanisms. We previously demonstrated that alcohol abuse induces an inflammatory immune response through Toll-like receptor 4 (TLR4), leading to structural and cognitive dysfunction. This study evaluated how TLR4 and sex as a variable (male/female) impact the lipidome of plasma-resident EVs after chronic alcohol exposure. Using a mouse model of chronic ethanol exposure in wild-type and TLR4-deficient mice, enrichment networks generated by LINEX2 highlighted significant ethanol-induced changes in the EV lipid substrate-product of enzyme reactions associated with glycerophospholipid metabolism. We also demonstrated ethanol-induced differences in Lipid Ontology enrichment analysis in EVs, focusing on terms related to lipid bilayer properties. A lipid abundance analysis revealed higher amounts of significant lipid subclasses in all experimental comparisons associated with inflammatory responses and EV biogenesis/secretion. These findings suggest that interrogating EV lipid abundance with a sensitive lipidomic-based strategy can provide deep insight into the molecular mechanisms underlying biological processes associated with sex, alcohol consumption, and TLR4 immune responses and open new avenues for biomarker identification and therapeutic development.

Distributional learning drives statistical deafening
Humans and other animals use information about how likely it is for something to happen. The absolute and relative probability of an event influences a remarkable breadth of behaviors, from foraging for food to comprehending linguistic constructions -- even when these probabilities are learned implicitly. It is less clear how, and under what circumstances, statistical learning of simple probabilities might drive changes in perception and cognition. Here, across a series of 29 experiments, we probe listeners' sensitivity to task-irrelevant changes in the probability distribution of tones' acoustic frequency across tone-in-noise detection and tone duration decisions. We observe that the task-irrelevant frequency distribution influences the ability to detect a sound and the speed with which perceptual decisions are made. The shape of the probability distribution, its range, and a tone's relative position within that range impact observed patterns of suppression and enhancement of tone detection and decision making. Perceptual decisions are also modulated by a newly discovered perceptual bias, with lower frequencies in the distribution more often and more rapidly perceived as longer, and higher frequencies as shorter. Perception is sensitive to rapid distribution changes, but distributional learning from previous probability distributions also carries over. In fact, massed exposure to a single point along the dimension results in a sustained 'statistical deafening' along a range of subsequently encountered frequencies. This seemingly maladaptive loss of sensitivity - occurring entirely in the absence of feedback or reward - points to a gain mechanism that suppresses sensitivity to regions along a perceptual dimension that are less likely to be encountered.

Addressing inconsistency in functional neuroimaging: A replicable data-driven multi-scale functional atlas for canonical brain networks
The advent of various neuroimaging methodologies has greatly aided in the conceptualization of large-scale brain networks in the field of cognitive neuroscience. However, there is inconsistency across studies in both nomenclature and the functional entities being described. There is a need for a unifying framework which standardizes terminology across studies while also bringing analyses and results into the same reference space. Here we present a functional whole-brain atlas of canonical brain networks derived from more than 100k resting-state fMRI datasets. These data-driven networks are highly replicable across datasets as well as multiple spatial scales. We have organized, labeled, and described them with terms familiar to the fields of cognitive and affective neuroscience in order to optimize their utility in future neuroimaging analyses and enhance the accessibility of new findings. The benefits of this atlas are not limited to future template-based or reference-guided analyses, but also extend to other data-driven neuroimaging approaches across modalities, such as those using blind independent component analysis (ICA). Future studies utilizing this atlas will contribute to greater harmonization and standardization in functional neuroimaging research.

Identifying Functional Homologues in Human and Marmoset Brain Networks via Movie-Driven Ultra-High Field fMRI
Numerous task-based functional magnetic resonance imaging (fMRI) studies have demonstrated that complex neural functions such as language processing, action observation, face recognition, and motor coordination are governed by widespread, intricate networks that span both cortical and subcortical areas. Nonhuman primate models are indispensable for advancing our understanding of the evolution of these networks and provide unique opportunities for experimental interventions that are not feasible in humans. In this study, we utilized movie-driven fMRI (md-fMRI) to investigate and delineate homologous functional networks in the common marmoset (Callithrix jacchus). Both marmosets and human subjects watched the same movie which incorporated a variety of visual and auditory stimuli. This method enabled the identification of potential homologues of large-scale functional networks involved in visual, auditory, cognitive, motor, and limbic functions in marmosets, offering new insights into the shared neurofunctional architecture across species.

Evaluating noise correction approaches for non-invasive electrophysiology of the human spinal cord
The spinal cord is a vital component of the central nervous system for the processing of sensorimotor information transmitted between the body and the brain. Electrospinography (ESG) is the most accessible non-invasive technique for recording spinal signals in humans, but the vast and detrimental impact of physiological noise (mostly of cardiac nature) has prevented widespread adoption. Here, we aim to address this issue by examining various denoising algorithms for cardiac artefact reduction - including principal component analysis-based techniques (PCA), independent component analysis-based approaches (ICA) and signal space projection (SSP). We observed that in situations where large numbers of spinal electrodes are used, SSP offers the best results in terms of balancing the removal of harmful noise and preserving neural information of interest. In cases where only a small number of electrodes are available, an approach based on PCA is deemed helpful. Approaches based on ICA were found to be unsuitable for cardiac artefact removal in ESG, due to a suboptimal balance of artefact removal and signal preservation. Finally, we also approached this issue from a signal-enhancement perspective and observed that in cases where extensive electrode arrays are used in the context of task-based designs, a spatial filtering technique based on canonical correlation analysis (CCA) reveals clear evoked spinal potentials even with single-trial resolution. Taken together, there are several appropriate algorithms for physiological noise removal in ESG, rendering this an accessible and easy-to-use technique for non-invasive assessments of human spinal cord function.

Time-on-task-related decrements in performance in the rodent continuous performance test are not caused by physical disengagement from the task
Attention deficits, a hallmark of many neuropsychiatric disorders, significantly impair quality of life and functional outcome for patients. Continuous Performance Tests (CPTs) are widely used to assess attentional function in clinical settings and have been adapted for mice as the rodent Continuous Performance Test (rCPT). In this study, we combined traditional analyses of rCPT performance with markerless pose estimation using DeepLabCut and visual field analysis (VFA) to objectively measure the orientation of mice toward stimuli during rCPT sessions. Additionally, we extended session lengths to assess performance decrements over time. Our findings show that extending rCPT sessions from 45 to 90 minutes results in a significant decline in performance in male mice, which aligns with performance decrements observed in clinical research. Importantly, physical engagement with the task remained relatively stable throughout the session, even as performance deteriorated. This suggests that the performance decline specifically reflects a time-on-task (TOT)-dependent vigilance decrement rather than physical disengagement. We also investigated the effects of amphetamine, an FDA-approved treatment for attention-deficit/hyperactivity disorder (ADHD), on rCPT performance. Amphetamine significantly improved rCPT performance in male mice by reducing false alarms without modulating orientation or physical engagement with the task stimuli. Collectively, these findings validate a behavioral tracking platform for objectively measuring physical engagement in the rCPT and a task modification that accentuates TOT-dependent performance decrements, enhancing the translational value of the rCPT for studies related to human neuropsychiatric disorders.

Fixation Drift Increases as a Function of Time-on-Task
Ocular fixations contain microsaccades, drift and tremor. We report an increase in the slope of linear fixation drift as a function of time-on-task (TOT). We employed a very large dataset (322 distinct subjects, multiple visits per subject). Subjects performed a random saccade task. The task, in which the target dot jumped randomly over the display area every 1 sec, was 100 sec in duration. Fixations were identified using a published classification method. For each fixation, we regressed eye position against time across multiple segment lengths (50, 100, 200, 300, 400, and 500 ms). We started with the first sample and continued until no further regressions were possible based on the particular segment length being evaluated. For each segment length, each fixation was characterized by a single value: the maximum slope over the segment length. The slopes were expressed in deg/sec. We were not interested in the direction of the linear drift so we took the absolute value of the slope as the measure. For data analysis, each 100 sec task was divided into five 20 sec epochs. We found that median slope increased across epochs in both session recordings. Although similar trends were found regardless of segment length, the results were clearer and more consistent when using segment lengths of 200 ms or greater. Although we describe these changes in linear drift as related to time-on-task (TOT), we think it is likely, though no certain, that these effects are due to some sort of short-term oculomotor fatigue.

Newly Acquired Word-Action Associations Trigger Auditory Cortex Activation During Movement Preparation: Implications for Hebbian Plasticity in Action Words Learning
Hebbian learning is believed to play a key role in acquisition of action words. However, this biological mechanism requires activation of the neural assemblies representing a word form and a corresponding movement to repeatedly overlap in time. In reality, though, these associated events could be separated by seconds. In the current MEG study, we examined trial-and-error learning of associations between novel auditory pseudowords and movements of specific body parts. We aimed to explore how the brain bridges the temporal gap between the transient activity evoked by auditory input and the preparatory motor activation before the corresponding movement. To address this, we compared learning-induced changes in neuromagnetic responses locked to the onset of the stimulus and to the onset of the movement. As learning progressed, both types of neural responses showed sustained enhancement during the delay period between the auditory pseudoword and the required movement. Cortical sources of this learning-induced increase were localized bilaterally in the lateral and medial temporal cortices. Notably, the learning effect was significantly stronger when measured time-locked to the movement onset, rather than to the pseudoword onset. This suggests that, after the pseudoword-movement associations were reliably acquired, the non-primary auditory cortex was reactivated in sync with the preparation of the upcoming movement. Such reactivation likely served to bring together in time the representations of the correct action and the preceding auditory cue. This temporal alignment could enable Hebbian learning, leading to long-lasting synaptic changes in temporally correlated neural assemblies.

The effect of unilateral hand muscle contraction on frontal alpha asymmetry and inhibitory control in intrinsic reward contexts, a randomized controlled trial
Challenged inhibitory control has been implicated in various disorders, including addiction. Previous research suggests that asymmetry of frontal brain activity, indexed by frontal alpha asymmetry (FAA), is associated with inhibitory control and could be a target for neuromodulatory intervention. Some evidence suggests that unilateral muscle contraction (UMC) can modulate FAA; however, experimental evidence is scarce. We conducted a randomized controlled trial, with 65 participants (Mage = 26.6; SD = 7.4), 37 of whom were females. We collected EEG data to calculate FAA and assessed inhibitory performance using the Stop Signal Task (SST) in neutral and intrinsic reward (palatable food) conditions, both before and after a unilateral left-hand muscle contraction task aimed at enhancing right relative to left frontal activity. We found a significant main effect of group on FAA. Specifically, UMC group was associated with higher right relative to left frontal activity, associated with resting state inhibitory activity. Event-related potential analyses revealed a significant dissociation between the stop N2 and stop P3 components as a function of time. More specifically, as time progressed, the stop N2 was enhanced, while the stop P3 was reduced. These results did not lead to observable changes in the behavioral index of stopping. In conclusion, UMC did not affect any behavioral and brain activity indices. There is some indication of a potential effect on FAA. However, this effect could reflect coincidental differences in trait FAA. Our findings provide new insights into the temporal dynamics of brain activity indices of inhibitory control.

A trans-synaptic IgLON adhesion molecular complex directly contacts and clusters a nicotinic receptor
The localization and clustering of neurotransmitter receptors at appropriate postsynaptic sites is a key step in the control of synaptic transmission. Here, we identify a novel paradigm for the synaptic localization of an ionotropic acetylcholine receptor (AChR) based on the direct interaction of its extracellular domain with a cell adhesion molecule of the IgLON family. Our results show that RIG-5 and ZIG-8, which encode the sole IgLONs in C. elegans, are tethered in the pre- and postsynaptic membranes, respectively, and interact in vivo through their first immunoglobulin-like (Ig) domains. In addition, ZIG-8 traps ACR-16 via a direct cis-interaction between the ZIG-8 Ig2 domain and the base of the large extracellular AChR domain. Such mechanism has never been reported, but all these molecules are conserved during evolution. Similar interactions may directly couple Ig superfamily adhesion molecules and members of the large family of Cys-loop ionotropic receptors, including AChRs, in the mammalian nervous system, and may be relevant in the context of IgLON-associated brain diseases.

Dynamic estimation of the attentional field from visual cortical activity
Navigating around the world, we must adaptively allocate attention to our surroundings based on anticipated future stimuli and events. This allocation of spatial attention boosts visuocortical representations at attended locations and locally enhances perception. Indeed, spatial attention has often been analogized to a 'spotlight' shining on the item of relevance. Although the neural underpinnings of the locus of this attentional spotlight have been relatively well studied, less is known about the size of the spotlight: to what extent can the attentional field be broadened and narrowed in accordance with behavioral demands? In this study, we developed a paradigm for dynamically estimating the locus and spread of covert spatial attention, inferred from visuocortical activity using fMRI in humans. We measured BOLD activity in response to an annulus while participants (4 female, 4 male) used covert visual attention to determine whether more numbers or letters were present in a cued region of the annulus. Importantly, the width of the cued area was systematically varied, calling for different sizes of the attentional spotlight. The deployment of attention was associated with an increase in BOLD activity in corresponding retinotopic regions of visual areas V1-V3. By modeling the visuocortical attentional modulation, we could reliably recover the cued location, as well as a broadening of the attentional enhancement with wider attentional cues. This modeling approach offers a useful window into the dynamics of attention and spatial uncertainty.

Drift in Individual Behavioral Phenotype as a Strategy for Unpredictable Worlds
Individuals, even with matched genetics and environment, show substantial phenotypic variability. This variability may be part of a bet-hedging strategy, where populations express a range of phenotypes to ensure survival in unpredictable environments. In addition phenotypic variability between individuals ("bet-hedging"), individuals also show variability in their phenotype across time, even absent external cues. There are few evolutionary theories that explain random shifts in phenotype across an animals life, which we term drift in individual phenotype. We use individuality in locomotor handedness in Drosophila melanogaster to characterize both bet-hedging and drift. We use a continuous circling assay to show that handedness spontaneously changes over timescales ranging from seconds to the lifespan of a fly. We compare the amount of drift and bet-hedging across a number of different fly strains and show independent strain specific differences in bet-hedging and drift. We show manipulation of serotonin changes the rate of drift, indicating a potential circuit substrate controlling drift. We then develop a theoretical framework for assessing the adaptive value of drift, demonstrating that drift may be adaptive for populations subject to selection pressures that fluctuate on timescales similar to the lifespan of an animal. We apply our model to real world environmental signals and find patterns of fluctuations that favor random drift in behavioral phenotype, suggesting that drift may be adaptive under some real world conditions. These results demonstrate that drift plays a role in driving variability in a population and may serve an adaptive role distinct from population level bet-hedging.

Structured and unstructured reactivations during REM sleep are modulated by novel experiences
Mammalian sleep is composed of two distinct phases characterized by unique neural activity patterns: rapid eye movement (REM) and non-REM (nREM) sleep. While both phases are essential for memory consolidation, neural replay of awake experience as a candidate mechanism for memory consolidation has only been shown for nREM sleep and it remains unclear whether awake experiences are reactivated during REM sleep. Here, we evaluated whether awake experiences are reactivated by hippocampal CA1 pyramidal neurons during REM sleep using a combination of approaches including Bayesian decoding, sequence factorization, and co-activation analysis. We confirmed that representations of awake exploration are recapitulated during subsequent REM episodes with varying levels of temporal structure. We also found that temporally organized sequences were replayed with a higher frequency during REM sleep following a novel experience. Finally, we find internalized structure in CA1 activity prior to novel task exposure that is expressed in subsequent behaviour. Altogether, these results suggest that while hippocampal ensembles appear as a result of structural priors, salient experiences refine temporal sequences during subsequent REM sleep, suggesting a unique role for REM sleep in salient-experience consolidation.

Trained deep neural network models of the ventral visual pathway encode numerosity with robustness to object and scene identity
"Number sense", the ability to quickly estimate quantities of objects in a visual scene, is present in humans and many other animals, and has recently been demonstrated in biologically inspired vision models, even before training. However, real-world number perception requires abstraction from the properties of individual objects and their contexts, in contrast to the simplified dot patterns used in previous studies. Using novel, synthetically generated photorealistic stimuli, we discovered that deep convolutional neural networks optimized for object recognition can encode numerical information across varying object and scene identities in their distributed activity patterns. In contrast, untrained networks failed to discriminate numbers, and appeared to encode low-level visual summary statistics of scenes rather than the number of discrete objects per se. These results caution against using untrained networks to model early numerical abilities and highlight the need to use more complex stimuli to understand the mechanisms behind the brain's visual number sense.

Hyperglycemia selectively increases cerebral non-oxidative glucose consumption without affecting blood flow
Multiple studies have shown that hyperglycemia increases the cerebral metabolic rate of glucose (CMRglc) in subcortical white matter. This observation remains unexplained. Using positron emission tomography (PET) and euinsulinaemic glucose clamps, we found, for the first time, that acute hyperglycemia increases non-oxidative CMRglc (i.e., aerobic glycolysis (AG)) in subcortical white mater as well as in medial temporal lobe structures, cerebellum and brainstem, all areas with low euglycemic CMRglc. Surprisingly, hyperglycemia did not change regional cerebral blood flow (CBF), the cerebral metabolic rate of oxygen (CMRO2), or the blood-oxygen-level-dependent (BOLD) response. Regional gene expression data reveal that brain regions where CMRglc increased have greater expression of hexokinase 2 (HK2). Simulations of glucose transport revealed that, unlike hexokinase 1, HK2 is not saturated at euglycemia, thus accommodating increased AG during hyperglycemia.

Age-associated transcriptomic and epigenetic alterations in mouse hippocampus
Aging represents a major risk for human neurodegenerative disorders, such as dementia and Alzheimers disease, and is associated with a functional decline in neurons and impaired synaptic plasticity, leading to a gradual decline in memory. Previous research has identified molecular and functional changes associated with aging through transcriptomic studies and neuronal excitability measurements, while the role of chromatin-level regulation in vulnerability to aging-related diseases is not well understood. Moreover, the causal relationship between molecular alterations and aging-associated decline in functions of different cell types remains poorly understood. Here, we systematically characterized gene regulatory networks in a cell type-specific manner in the aging mouse hippocampus, a central brain region involved in learning and memory formation, by simultaneously profiling gene expression and chromatin accessibility at a single nuclei level. The analysis of multiome (RNA and ATAC) sequencing recapitulated the diversity of glial and neuronal cell types in the hippocampus, and allowed revealing transcriptomic and chromatin accessibility level changes in different cell types, among which oligodendrocytes and dentate gyrus (DG) neurons exhibited the most drastic changes. We found that aging-dependent chromatin-level changes were more pronounced than transcriptomic changes for genes related to synaptic plasticity among neurons. Our data suggest that BACH2, a candidate transcription factor in the aging-mediated functional decline of DG neurons, potentially regulates genes associated with synaptic plasticity, cell death, and inflammation during aging.

Mapping the topographic organization of the human zona incerta using diffusion MRI
The zona incerta (ZI) is a deep brain region originally described by Auguste Forel as an "immensely confusing area about which nothing can be said." Despite the elusive nature of this structure, mounting evidence supports the role of the ZI and surrounding regions across a diverse range of brain functions and as a candidate target for neuromodulatory therapies. Using in vivo diffusion MRI and data-driven connectivity, we identify a topographic organization between the ZI and neocortex. Specifically, our methods identify a rostral-caudal gradient predominantly connecting the frontopolar and ventral prefrontal cortices with the rostral ZI, and the primary sensorimotor cortices with the caudal ZI. Moreover, we demonstrate how clustering and gradient approaches build complementary evidence including facilitating the mapping of a central region of the ZI, connected with the dorsal prefrontal cortex. These results were shown to be replicable across multiple datasets and at the individual subject level, building evidence for the important role of the ZI in mediating frontal lobe-associated tasks, ranging from motor to cognitive to emotional control. Finally, we consider the impact of this topographic organization on the refinement of neuromodulatory targets. These results pave the way for an increasingly detailed understanding of ZI substructures, and considerations for in vivo targeting of the ZI for neuromodulation.

Presence of distinct operant phenotypes and transient withdrawal-induced escalation of operant ethanol intake in female rats
Operant self-administration is frequently used to investigate the neurobiological mechanisms underlying alcohol seeking and drinking and to test the efficacy of drugs under development for the treatment of alcohol use disorder (AUD). Although widely used by the research community, there is a paucity of operant ethanol self-administration studies that include female subjects. The current study characterizes home cage drinking and operant ethanol self-administration in female Sprague Dawley, Long Evans, and Wistar rats. Rats underwent three weeks of intermittent-access two-bottle choice home cage drinking before being trained to lever press for ethanol in standard operant chambers equipped with contact lickometers. After capturing baseline operant performance, rats were chronically exposed to control or ethanol liquid diet using the Lieber-DeCarli method. Operant ethanol self-administration was re-evaluated after chronic liquid diet exposure to determine whether female rats exhibit similar withdrawal-induced escalation of ethanol intake as is regularly observed in male rats. Our findings reveal the presence of three distinct operant phenotypes (Drinker, Responder, Nonresponder), the prevalence of which within each strain is strikingly similar to our previous observations in males. Within a given phenotype, rats of each strain performed similarly during operant testing. Ethanol intake during home cage drinking was unable to predict future operant phenotype. Relative to controls, Drinkers chronically exposed to ethanol liquid diet exhibited a significant, but transient, escalation in consummatory, but not appetitive, responding during acute withdrawal. Collectively, these data closely parallel many of our previous observations in males while also highlighting potential sex differences in drinking strategies following dependence. The presence of the Responder phenotype reinforces the importance of using direct measures of ethanol consumption. Our findings provide new insight into similarities and differences in operant ethanol self-administration between males and females and emphasize the importance of including females in future studies of ethanol drinking and dependence.

Glia multitask to compensate for neighboring glial cell dysfunction
As glia mature, they undergo glial tiling to abut one another without invading each other's boundaries. Upon the loss of the secreted neurotrophin Sptazle3 (Spz3), Drosophila cortex glia transform morphologically and lose their intricate interactions with neurons and surrounding glial subtypes. Here, we reveal that all neighboring glial cell types (astrocytes, ensheathing glia, and subperineurial glia) react by extending processes into the previous cortex glial territory to compensate for lost cortex glial function and reduce the buildup of neuronal debris. However, the loss of Spz3 alone is not sufficient for glia to cross their natural borders, as blocking CNS growth via nutrient-restriction blocks the aberrant infiltration induced by the loss of Spz3. Surprisingly, even when these neighboring glia divert their cellular resources beyond their typical borders to take on new compensatory roles, they are able to multitask to continue to preserve their own normal functions to maintain CNS homeostasis.

Semaglutide Administration in Healthy Mice Alters Behaviour Related to Stress and Motivation
Semaglutide, a GLP-1 receptor agonist used primarily to regulate blood sugar and appetite, has been studied mostly in models of obesity and diabetes. Yet, little is known about its effects on healthy animals. In this study, daily dosing of semaglutide (0.1 mg/kg) in healthy C57BL/6JRj male wildtype mice led to noticeable changes in behavioural tests commonly used to evaluate stress and motivation. The mice showed increased jumping in the open field, reduced shredding of nestlets, less interest in sniffing female urine, and heightened activity in the forced swim test. These behavioural shifts may indicate potential side effects of semaglutide in healthy animals, providing a crucial baseline for understanding how the drug could affect conditions like obesity, addiction, or cognitive decline.

CD300f immune receptor is a microglial tissue damage sensor and regulates efferocytosis after brain damage
Microglia, the resident phagocytes of the central nervous system (CNS), continuously monitor the parenchyma and surrounding borders and are the primary responders to brain damage. CD300f is a lipid-sensing immunoreceptor present in the microglial cell membrane, which binds to phosphatidylserine and other lipid mediators. Defining the functional microglial sensome is critical to understand their function and cell state determination. Using intravital two-photon microscopy we show that microglia lacking the CD300f receptor fail to detect environmental damage cues after a laser ablation injury. After a mild traumatic brain injury or after the intracortical injection of apoptotic cells, CD300f-/- microglia showed reduced capacity for detecting and phagocytosing dyeing cells, leading to the accumulation of dead cells in the neural parenchyma. Moreover, at later timepoints, increased accumulation of dyeing cells was found inside CD300f-/- microglia in vivo and in bone marrow-derived macrophages in vitro, suggesting that these cells display a reduced capacity for metabolizing phagocytosed cells. Finally, CD300f deficiency increased functional compromise after a contusive traumatic brain injury, associated to increased conservation of brain tissue. Collectively, these results suggest that CD300f function as a damage-associated molecular pattern (DAMP) receptor that coordinates microglial process reaction towards tissue debris and highlights its central role in microglial sensome machinery and in the modulation of in vivo microglial efferocytosis.

A physiologically inspired hybrid CPG/Reflex controller for cycling simulations that generalizes to walking
Predictive simulations based on explicit, physiologically inspired, control policies, can be used to test theories on motor control and to evaluate the effect of interventions on the different components of control. Several control architectures have been proposed for simulating locomotor tasks, based on fully feedback, reflex-based, controllers, or on feedforward architectures mimicking the Central Pattern Generators. Recently, hybrid architectures integrating both feedback and feedforward components have been shown to represent a viable alternative to fully feedback or feedforward controllers. Current literature on controller-based simulations, however, almost exclusively presents task-specific controllers that do not generalize across different tasks. The task-specificity of current controllers limits the generalizability of the neurophysiological principles behind such controllers. Here we propose a hybrid controller for predictive simulations of cycling based where the feedforward component is based on a well-known theoretical model, the Unit Burst Generation model, and the feedback component includes a limited set of reflex pathways, expected to be active during submaximal steady cycling. We show that this controller can simulate physiological cycling patterns at different desired speeds. We also show that the controller can generalize to walking behaviors by just adding an additional control component for accounting balance needs. The controller here proposed, although simple in design, represent an instance of physiologically inspired generalizable controller for cyclical lower limb tasks.

There is no Biophysical Distinction between Temporal Interference Stimulation and Direct kHz Stimulation for Actuation of Peripheral Nerves
Temporal interference stimulation (TIS) has attracted increasing attention as a promising noninvasive electrical stimulation method. Despite positive results and optimistic expectations, the TIS field has been beset by misunderstandings concerning its mechanism of action and efficacy in safely targeting deep neural structures. Various studies posit that TIS exploits the interference of multiple supraphysiological frequency (kHz range) carriers to essentially deliver low-frequency stimulation at the intersection of the carriers, thereby circumventing limitations associated with tissue impedance and depth penetration. Due to the documented electrophysiological effects of kHz-range electric stimuli, such a picture is an oversimplification. Moreover, recent theoretical modelling work has established that the biophysics of TIS is based on kHz stimulation mechanisms. This paper presents experimental evidence supporting this conclusion, by comparing TIS with direct kHz stimulation on peripheral nerve targets in an invertebrate model (Locusta migratoria), and in human subjects. Our findings show that the stimulation effects of TIS are achievable through two-electrode kHz stimulation, without necessitating carrier interference in tissue. By comparing four-electrode TIS with two-electrode stimulation via kHz sine waves for targeting of peripheral nerves, we demonstrate overlapping strength-frequency (s-f) dependence across all stimulation types. Since all stimulation waveforms are governed by the same s-f curve, this implicates a common underlying biophysical mechanism. This equivalence challenges the notion that TIS uniquely facilitates neural engagement via other mechanisms. Furthermore, performing TIS with higher carrier frequencies into the MHz range fails to lead to stimulation. We evaluate the regions of tonic (unmodulated) and phasic (amplitude-modulated) stimulation regions inherent when using TIS, and the associated possibility of off-target effects. Our study further suggests that possible practical advantages of TIS can be achieved in an easier way by simply using amplitude-modulated kHz waveforms.

DendroTweaks: An interactive approach for unraveling dendritic dynamics
Neurons rely on the interplay between dendritic morphology and ion channels to transform synaptic inputs into a sequence of somatic spikes. Detailed biophysical models with active dendrites have been instrumental in exploring this interaction. However, such models can be challenging to understand and validate due to the large number of parameters involved. In this work, we introduce DendroTweaks -- a toolbox designed to illuminate how morpho-electric properties map to dendritic events and how these dendritic events shape neuronal output. DendroTweaks features a web-based graphical interface, where users can explore single-cell neuronal models and adjust their morphological and biophysical parameters with real-time visual feedback. In particular, DendroTweaks is tailored to interactive fine-tuning of subcellular properties, such as kinetics and distributions of ion channels, as well as the dynamics and allocation of synaptic inputs. It offers an automated approach for standardization and refinement of voltage-gated ion channel models to make them more comprehensible and reusable. The toolbox allows users to run various experimental protocols and record data from multiple dendritic and somatic locations, thereby enhancing model validation. Finally, it aims to deepen our understanding of which dendritic properties are essential for neuronal input-output transformation. Using this knowledge, one can simplify models through a built-in morphology reduction algorithm and export them for further use in faster, more interpretable networks. With DendroTweaks, users can gain better control and understanding of their models, advancing research on dendritic input-output transformations and their role in network computations.