bioRxiv Subject Collection: Neuroscience's Journal

Changes in interlimb coordination induced by within-stride changes in treadmill speed
During walking, interlimb coordination involves the right and left legs working together to achieve a desired movement. Previously, dynamic treadmill walking has been shown to drive asymmetric gait changes in healthy young adults through selectively changing the speed of the whole treadmill. Currently, the coordination demands of this novel walking environment are unknown and must be understood prior to assessing dynamic treadmill walking in clinical populations. We investigated the interlimb coordination requirements of dynamic treadmill walking in ten healthy young adults. We quantified interlimb coordination changes as phase shift (the time for a maximum cross-correlation between limb angle trajectories of the left and right legs), center of oscillation (limb angle at midstance), and center of oscillation difference (oscillation angle difference between legs). We found that phase shift in the Fast trial (i.e., 1.0m/s treadmill speed in first 50% of gait cycle, 0.5m/s in latter 50%) was significantly more positive (i.e., the right leg oscillates ahead of the left leg in time) than in the Slow, Accelerate, and Decelerate conditions (all p<0.01). The Fast trial produced significantly positive center of oscillation values on the right leg, indicating that the right leg is oscillating about a more flexed axis than the left. Center of oscillation difference was similarly more positive during the Fast trial than in the Decelerate (p<0.01) and Slow (p<0.01) trials. These results exemplify that some forms of dynamic treadmill walking change interlimb coordination to a greater extent than others. After several minutes of dynamic treadmill walking, interlimb coordination is changed relative to baseline walking in the spatial domain (Fast and Decelerate conditions) and the temporal domain (Fast and Slow). Therefore, dynamic treadmill walking is tunable in both biomechanical and interlimb coordination parameters, creating a variety of options for restoring gait symmetry in asymmetric populations.

Born Connected: Do Infants Already Have Adult-Like Multi-Scale Connectivity Networks?
The human brain undergoes remarkable development with the first six postnatal months witnessing the most dramatic structural and functional changes, making this period critical for in-depth research. rsfMRI studies have identified intrinsic connectivity networks (ICNs), including the default mode network, in infants. Although early formation of these networks has been suggested, the specific identification and number of ICNs reported in infants vary widely, leading to inconclusive findings. In adults, ICNs have provided valuable insights into brain function, spanning various mental states and disorders. A recent study analyzed data from over 100,000 subjects and generated a template of 105 multi-scale ICNs enhancing replicability and generalizability across studies. Yet, the presence of these ICNs in infants has not been investigated. This study addresses this significant gap by evaluating the presence of these multi-scale ICNs in infants, offering critical insight into the early stages of brain development and establishing a baseline for longitudinal studies. To accomplish this goal, we employ two sets of analyses. First, we employ a fully data-driven approach to investigate the presence of these ICNs from infant data itself. Towards this aim, we also introduce burst independent component analysis (bICA), which provides reliable and unbiased network identification. The results reveal the presence of these multi-scale ICNs in infants, showing a high correlation with the template (rho > 0.5), highlighting the potential for longitudinal continuity in such studies. We next demonstrate that reference-informed ICA-based techniques can reliably estimate these ICNs in infants, highlighting the feasibility of leveraging the NeuroMark framework for robust brain network extraction. This approach not only enhances cross-study comparisons across lifespans but also facilitates the study of brain changes across different age ranges. In summary, our study highlights the novel discovery that the infant brain already possesses ICNs that are widely observed in older cohorts.

Rapid Semantic Processing: An MEG Study of Narrative Text Reading
Research has shown that semantic analysis occurs at early stages of word processing (less than 200 ms). While traditional studies have focused on isolated words/sentences, our research explores rapid semantic processing during reading stories using event-related potentials and magnetoencephalography. We employed the rapid serial visual presentation paradigm to present texts word by word. Each word presentation lasted 150 ms, enhancing rapid semantic processing. We computed semantic dissimilarity (SD) values for each word and categorized them into quartiles to investigate their effect on brain responses. Our analysis revealed significant ERP differences within early time windows (120-132 ms). Two distinct clusters were identified: positive in the right occipital region and negative in the left temporal region. In both clusters less pronounced responses were registered for words with lowest SD which corresponds to theories of predictive coding. These findings broaden our understanding of rapid semantic processing and suggest new methodology.

Sensory Entrained TMS (seTMS) enhances motor cortex excitability
Transcranial magnetic stimulation (TMS) applied to the motor cortex has revolutionized the study of motor physiology in humans. Despite this, TMS-evoked electrophysiological responses show significant variability, due in part to inconsistencies between TMS pulse timing and ongoing brain oscillations. Variable responses to TMS limit mechanistic insights and clinical efficacy, necessitating the development of methods to precisely coordinate the timing of TMS pulses to the phase of relevant oscillatory activity. We introduce Sensory Entrained TMS (seTMS), a novel approach that uses musical rhythms to synchronize brain oscillations and time TMS pulses to enhance cortical excitability. Focusing on the sensorimotor alpha rhythm, a neural oscillation associated with motor cortical inhibition, we examine whether rhythm-evoked sensorimotor alpha phase alignment affects primary motor cortical (M1) excitability in healthy young adults (n=33). We first confirmed using electroencephalography (EEG) that passive listening to musical rhythms desynchronizes inhibitory sensorimotor brain rhythms (mu oscillations) around 200 ms before auditory rhythmic events (27 participants). We then targeted this optimal time window by delivering single TMS pulses over M1 200 ms before rhythmic auditory events while recording motor-evoked potentials (MEPs; 19 participants), which resulted in significantly larger MEPs compared to standard single pulse TMS and an auditory control condition. Neither EEG measures during passive listening nor seTMS-induced MEP enhancement showed dependence on musical experience or training. These findings demonstrate that seTMS effectively enhances corticomotor excitability and establishes a practical, cost-effective method for optimizing non-invasive brain stimulation outcomes.

Pupil size variations reveal Bayesian inference in cognitive arithmetic
The assumption that the brain relies on Bayesian inference has been successful in accounting for many behavioural and neurophysiological observations, but to date, dependence on such mechanism has not been assessed in the context of arithmetic. Bayesian inference implies the representation of uncertainty and reliance on prior beliefs. In arithmetic problem solving, it would consist in refining prior knowledge about the response range as the system progressively integrates the numerical information conveyed by the operands. Within this framework, the amount of information needed to progress from a prior to a posterior probability distribution over responses can be quantified by the information gain, which would relate to the cognitive workload of the task. To test this hypothesis, we designed three experiments in which participants computed the sum of two numbers presented one after another through headphones. In each experiment, the information about response predictability conveyed by the first operand was manipulated. The first operand was either highly informative and contributed to narrow down the response range, or poorly informative and conveyed little information about a plausible response. Throughout all experiments, we found that pupil-related arousal signalled the information gain associated with the first operand, indicating that participants already updated the probability distribution of possible responses upon hearing that first stimulus. This finding shows that Bayesian inference is central to arithmetic problem solving and that information gains consecutive to the integration of the operands can be tracked over time through pupillometry.

Rac1 inhibition prevents axonal cytoskeleton dysfunction in Transthyretin Amyloid Polyneuropathy
Transthyretin Amyloid Polyneuropathy (ATTR-PN) is characterized by the deposition of amyloidogenic TTR, particularly in dorsal root ganglia (DRG) and peripheral nerve axons, resulting in sensory axonopathy. Here, we investigated the role of cytoskeleton alterations in peripheral axons from an ATTR-PN mouse model and searched for genetic modifiers in human patient samples. We employed the hTTRA97S knock-in mouse model for ATTR-PN to examine cellular and molecular changes in peripheral axons. Our approach combined proteomic analysis of the sural nerve, live imaging techniques, and pharmacological intervention targeting Rac1. Additionally, DNA samples from individuals diagnosed with early- and late-onset ATTR-PN were analyzed to identify genetic variants in Rac1 and specific regulators potentially associated with the disease-onset. Guided by proteomics of the sural nerve of hTTRA97S mice, which revealed dysregulation of actin-related proteins, we investigated actin organization in mutant neurons. We found a defective actin distribution in growth cones from hTTRA97S DRG neurons, along with a reduction in axonal actin trails, and an associated impairment in the pool of pre-synaptic vesicles. Additionally, microtubule dynamics and axonal transport abnormalities were observed in mutant axons. Importantly, cytoskeletal defects in hTTRA97S neurons preceded axonal degeneration and were mediated by Rac1. Hyperactivation of Rac1 was observed in both hTTRA97S DRG neurites and sciatic nerves of pre-symptomatic mice, and its inhibition rescued cytoskeleton alterations, preventing subsequent degeneration. Remarkably, in ATTR-PN patients with late-onset disease, we identified a variant in the RACGAP1 gene, which encodes for a specific Rac1 inactivator, further supporting the neuroprotective role of Rac1 inhibition. Our findings demonstrate that cytoskeletal defects precede axonal degeneration in ATTR-PN and highlight Rac1 as a promising therapeutic target. The identification of a protective genetic variant in patients corroborates this potential, suggesting a new avenue for therapeutic intervention in ATTR-PN.

Individual differences in the effects of musical familiarity and musical features on brain activity during relaxation
Finding a way to relax is increasingly difficult in our overstimulating modern society and chronic stress can have severe psychological and physiological consequences. Music is a promising tool to promote relaxation by lowering heart rate, modulating mood and thoughts, and providing a sense of safety. Here, we used functional magnetic resonance imaging (fMRI) to investigate how music influence brain activity during relaxation with a particular focus on the participants' experience of different types of music. In a 2x2 design, 57 participants were scanned while rating how relaxed they felt after listening to 28-second excerpts of either familiar or unfamiliar relaxation music with calm or energetic features. Behaviourally, calm music was the strongest predictor of relaxation, followed by familiar music. fMRI results revealed activations of auditory, motor, emotion, and memory areas, for listening to familiar compared to unfamiliar music. This suggests increased audio-motor synchronization and participant engagement of known music. Listening to unfamiliar music was correlated with attention-related brain activity, suggesting increased attentional load for this music. Behaviourally, we identified four clusters of participants based on their relaxation response to the different types of music. These groups also displayed distinct auditory and motor activity patterns, suggesting that the behavioural responses are linked to changes in music processing. Interestingly, some individuals found energetic music to be relaxing if it is familiar, whereas others only found calm music to be relaxing. Such individual behavioural and neurological differences in relaxation responses to music emphasise the importance of developing personalised music-based interventions.

Chemotagging: a chemogenetic approach for identifying cell types with in vivo calcium imaging
The ability to monitor the activity of specific cell types in vivo is critical for understanding the complex interplay between various neuronal populations driving freely moving behavior. Existing methods, such as optogenetic tagging (i.e., Optotagging), have proven useful for identifying cell types in in vivo electrophysiological recordings during freely moving behavior. However, electrophysiological recordings are limited in their capacity to track the same neuronal populations across long periods of time (days to weeks). Single-photon miniscope imaging offers the advantage of tracking the same cells across weeks to months; however, it is difficult to distinguish different cell types within the recorded population. Here, we present "chemotagging," a technique that allows for the identification of specific cell types in in vivo calcium imaging recordings. This protocol offers a method for tagging cell types with chemogenetic tools like Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), while simultaneously recording calcium activity from a pan-neuronal population with calcium indicators. We highlight the key advantages and limitations of chemotagging and its potential implications for neuroscience research.

Dynamic consensus-building between neocortical areas via long-range connections
The neocortex is organized into functionally specialized areas. While the functions and underlying neural circuitry of individual neocortical areas are well studied, it is unclear how these regions operate collectively to form percepts and implement cognitive processes. In particular, it remains unknown how distributed, potentially conflicting computations can be reconciled. Here we show that the reciprocal excitatory connections between cortical areas orchestrate neural dynamics to facilitate the gradual emergence of a 'consensus' across areas. We investigated the joint neural dynamics of primary (V1) and higher-order lateromedial (LM) visual areas in mice, using simultaneous multi-area electrophysiological recordings along with focal optogenetic perturbations to causally manipulate neural activity. We combined mechanistic circuit modeling with state-of-the-art data-driven nonlinear system identification, to construct biologically-constrained latent circuit models of the data that we could further interrogate. This approach revealed that long-range, reciprocal excitatory connections between V1 and LM implement an approximate line attractor in their joint dynamics, which promotes activity patterns encoding the presence of the stimulus consistently across the two areas. Further theoretical analyses revealed that the emergence of line attractor dynamics is a signature of a more general principle governing multi-area network dynamics: reciprocal inter-area excitatory connections reshape the dynamical landscape of the network, specifically slowing down the decay of activity patterns that encode stimulus features congruently across areas, while accelerating the decay of inconsistent patterns. This selective dynamic amplification leads to the emergence of multi-dimensional consensus between cortical areas about various stimulus features. Our analytical framework further predicted the timescales of specific activity patterns across areas, which we directly verified in our data. Therefore, by linking the anatomical organization of inter-area connections to the features they reconcile across areas, our work introduces a general theory of multi-area computation.

Differential effects of statins on the anti-dyskinetic activity of sub-anesthetic ketamine
Sub-anesthetic ketamine has been demonstrated to reduce abnormal involuntary movements (AIMs) in preclinical models of L-DOPA-induced dyskinesia (LID) and retrospective Parkinson's disease case reports. In this study, we examined the effects on L-DOPA-induced dyskinesia of two statins alone and in combination with ketamine in unilateral 6-hydroxydopamine-lesioned male rats, the standard preclinical LID model. Sub-anesthetic ketamine attenuated the development of AIMs, while lovastatin only showed anti-dyskinetic activity at the beginning of the priming but did not prevent the development of LID. The polar pravastatin blocked the long-term anti-dyskinetic effects of ketamine, while the non-polar lovastatin did not. This study shows different classes of statins affect LID differentially, points to an important drug interaction and further supports ongoing clinical testing of sub-anesthetic ketamine to treat LID in individuals with Parkinson's disease.

Exploring Neural Dynamics in the Auditory Telencephalon of Crows using Functional Ultrasound Imaging
Crows, known for advanced cognitive abilities and vocal communication, rely on intricate auditory systems. While the neuroanatomy of corvid auditory pathways is partially explored, the underlying neurophysiological mechanisms are largely unknown. This study used functional ultrasound imaging (fUSi) to investigate sound-induced cerebral blood volume (CBV) changes in the field L complex of the crow's auditory telencephalon, a functional analogue to the mammalian auditory cortex. FUSi revealed frequency-specific CBV responses, showing a tonotopic organization within the field L complex, with low frequencies in the posterior-dorsal region and high frequencies in the anterior-ventral region, similar to neuronal patterns reported in other songbirds. The responses were more robust when the crows were awake compared to when they were anesthetized. Machine learning analyses showed fUSi signals could be used to classify sound types accurately. Shorter stimuli reliably triggered transient CBV increases, while longer sounds resulted in variable responses, including negative deflections. This variability in CBV responses suggests a delineation of subregions within the field L complex with the central region (L2) as the primary processing hub and outer regions (L1, L3) integrating auditory information. These findings highlight the potential of fUSi for providing high-resolution insights into functional systems in corvids, enabling future exploration of task-related cognitive dynamics.

White matter hyperintensities and microplastics
Synopsis: White matter hyperintensities are abnormalities that appear in MRI scans of living patients but are not apparent in MRI post-mortem. Goal: Our goal is to understand the cellular/biological basis of white matter hyperintensities (WMH). Approach: We aligned post-mortem MR scans with those collected ante-mortem and performed histopathology and pyrGC/MS for plastics on regions with WMH. Result: PyrGC/MS detected large amounts of plastics and we deterined their cellular locations with a novel optical imaging approach in regions with small vessel disease and Abeta plaques. Impact: Microplastics in the brains of people with cognitive impairment may be due to pre-existing vascular injury or contribute to it. Many questions remain: Where do they come from, do they impair function? Can they be diagnosed by MRI ante-mortem?

White matter microstructure links with brain, bodily and genetic attributes in adolescence, mid- and late life
Advanced diffusion magnetic resonance imaging (dMRI) allows one to probe and assess brain white matter (WM) organization and microstructure in vivo. Various dMRI models with different theoretical and practical assumptions have been developed, representing partly overlapping characteristics of the underlying brain biology with potentially complementary value in the cognitive and clinical neurosciences. To which degree the different dMRI metrics relate to clinically relevant geno- and phenotypes is still debated. Hence, we investigate how tract-based and whole WM skeleton parameters from different single- and multi-compartment dMRI approaches associate with clinically relevant and white matter-related phenotypes (sex, age, pulse pressure (PP), body-mass-index (BMI), brain asymmetry) and genetic markers in the UK Biobank (UKB, n=52,140) and the Adolescent Brain Cognitive Development (ABCD) Study (n=5,844). Multi-compartment dMRI approaches provided the strongest WM associations with age, and unique insights into brain asymmetry. Kurtosis was most indicative of PP and BMI. WM-based sex classifications and polygenic score associations for common psychiatric disorders and Alzheimer's disease were similar across diffusion approaches. We conclude that WM microstructure is differentially associated with clinically relevant pheno- and genotypes at different points in life. Multi-compartment dMRI approaches, and particularly the examined Bayesian approach, provide additional information to conventional approaches in such examinations.

A humanized neuronal model system reveals key roles for manganese in neuronal endocytosis, calcium flux and mitochondrial bioenergetics
Manganese (Mn) is an essential trace metal that is necessary for life. Its duality as both a crucial micronutrient and potential neurotoxicant necessitates tight control of intracellular and extracellular Mn levels. Dysregulation of Mn is implicated in a broad range of human diseases, from neurodevelopmental sequelae related to Mn levels in drinking water, to acquired forms of manganism, rare inherited Mn transportopathies and more common disorders such as Parkinson's and Alzheimer's disease. Despite the clear association between Mn dysregulation and neurodevelopmental or neurodegenerative diseases, the underlying cellular mechanisms that govern neuropathology remain poorly understood. We established an induced pluripotent stem cells-derived midbrain neuronal system from SLC39A14, SLC39A8, and SLC30A10 patients to better understand the neuronal sequelae of Mn dysregulation. By integrating transcriptomic and functional approaches, we show that Mn dyshomeostasis leads to dysregulation of key cellular pathways that are crucial to normal neuronal function, including defects in mitochondrial bioenergetics, calcium signalling, endocytosis, and glycosylation, as well as cellular stress and early neurodegeneration. Our humanized model has enhanced understanding of the role of Mn in the human brain, and the consequences of both acquired and genetic disorders associated with Mn dysregulation. Better understanding of these underlying pathophysiological processes will identify potential targets for future therapeutic intervention.

The Lifespan Evolution of Individualized Neurophysiological Traits
How do neurophysiological traits that characterize individuals evolve across the lifespan? To address this question, we analyzed brief, task-free magnetoencephalographic recordings from over 1,000 individuals aged 4-89. We found that neurophysiological activity is significantly more similar between individuals in childhood than in adulthood, though periodic patterns of brain activity remain reliable markers of individuality across all ages. The cortical regions most critical for determining individuality shift across neurodevelopment and aging, with sensorimotor cortices becoming increasingly prominent in adulthood. These developmental changes in neurophysiology align closely with the expression of cortical genetic systems related to ion transport and neurotransmission, suggesting a growing influence of genetic factors on neurophysiological traits across the lifespan. Notably, this alignment peaks in late adolescence, a critical period when genetic factors significantly shape brain individuality. Overall, our findings highlight the role of sensorimotor regions in defining individual brain traits and reveal how genetic influences on these traits intensify with age. This study advances our understanding of the evolving biological foundations of inter-individual differences.

Insulin resistance, cognition, and functional brain network topology in older adults with obesity
Objective: Cross-sectional data from a sample of older adults with obesity was used to determine how peripheral and neuronal insulin resistance (IR) relate to executive function and functional brain network topology. Methods: Older adults (n=71) with obesity but without type 2 diabetes were included in analyses. Peripheral IR was quantified by HOMA2-IR. Neuronal IR was quantified according to a proposed neuron-derived exosome-based method (NDE-IR). An executive function composite score, summed scores to the Auditory Verbal Learning Test (AVLT) trials 1-5, and functional brain networks generated from resting-state functional magnetic resonance imaging were outcomes in analyses. We used general linear models and a novel regression framework for brain network analysis to identify relationships between IR measures and brain-related outcomes. Results: HOMA2-IR, but not NDE-IR, was negatively associated with executive function. Neither IR measure was associated with AVLT score. Peripheral IR was also related to hippocampal network topology in participants who had undergone functional neuroimaging. Neither peripheral nor neuronal IR were significantly related to network topology of the central executive network. Conclusions: Cognitive and functional imaging effects were observed from HOMA2-IR, but not NDE-IR. The hippocampus may be particularly vulnerable to effects of peripheral IR.

UniSPAC: A Unified Segmentation Framework for Proofreading and Annotation in Connectomics
Reconstructing dense neuronal connections from volume electron microscopy (vEM) images is a critical challenge in neuroscience, driving the development of various automatic neuron segmentation methods. Although current state-of-the-art automated segmentation methods can achieve high segmentation accuracy, they still require substantial manual proofreading and rely heavily on labeled datasets, which are often scarce, particularly for non-model organisms. Here, we introduce a Unified Segmentation framework for Proofreading and Annotation in Connectomics (UniSPAC) by providing the interactive segmentation model in 2D-level and the neuron tracing model in 3D-level. UniSPAC-2D allows users to correct its segmentation errors through point-based prompts, combining segmentation and proofreading in a single framework. UniSPAC-3D automatically traces neurons segmented by UniSPAC-2D across image slices, significantly reducing human involvement. Furthermore, UniSPAC-2D and UniSPAC-3D models can facilitate the semi-automatic generation of labeled data for new species, eliminating the need for external annotation tools. The fresh annotated data generated during proofreading in turn optimizes the interactive model through an online learning strategy, reducing the labeling effort for novel species over time. UniSPAC outperforms the start-of-the-art Segment Anything Model (SAM) in Drosophila segmentation, achieving 47x higher efficiency, and surpasses ACRLSD in cross-species segmentation on zebra finch data.

Physioxia-modulated mesenchymal stem cells secretome has higher capacity to preserve neuronal network and translation processes in hypoxic-ischemic encephalopathy in vitro model
Hypoxic-ischemic encephalopathy (HIE) is one of the leading causes of child death worldwide. Most of the survivors develop various neurological diseases, such as cerebral palsy, seizures, and/or motor and behavioral problems. HIE is caused by an episode of perinatal asphyxia, which interrupts the blood supply to the brain. Due to its high energy demands, this interruption initiates glutamate excitotoxic pathways, leading to cell death. Umbilical cord mesenchymal stem cells (UC MSCs) are gaining attention as a promising complement to the current clinical approach, based on therapeutic hypothermia, which has shown limited efficacy. Previous data have shown that priming MSCs under physiological culture conditions, namely soft platforms (3kPa), mechanomodulated, or physiological oxygen levels (5% O2), physioxia, leads to changes in the cellular proteome and their secretome. To evaluate how exposing MSCs to these culture conditions could impact their therapeutic potential, physiologically primed UC MSCs or their secretome were added to an in vitro HIE model using cortical neurons primary cultures subjected to oxygen and glucose deprivation (OGD) insult. By comparing the neuronal proteome of sham, OGD insulted, and OGD-treated neurons, it was possible to identify proteins whose levels were restored in the presence of UC-MSCs or their secretome. Despite the different approaches that differentially altered UC-MSCs proteome and secretome, the effects converged on the re-establishment of the levels of proteins involved in translation mechanisms (such as the 40S and 60s ribosomal subunits), possibly stabilizing proteostasis, which is known to be essential for neuronal recovery. Interestingly, treatment with the secretome of UC-MSC modulated under physioxic conditions sustained part of the neuronal network integrity and modulated several mitochondrial proteins, including those proteins involved in ATP production. This suggests that the unique composition of the physioxia-modulated secretome may offer a therapeutical advantage in restoring essential cellular processes that help neurons maintain their function, compared to traditionally expanded UC-MSCs. These findings suggest that both the presence of UC-MSCs and their secretome alone can influence multiple targets and signaling pathways, collectively promoting neuronal survival following an OGD insult.

Systemic exposure to COVID-19 virus-like particles modulates firing patterns of cortical neurons in the living mouse brain
Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) causes a systemic infection that affects the central nervous system. We used virus-like particles (VLPs) to explore how exposure to the SARS-CoV-2 proteins affects brain activity patterns in wild-type (WT) mice and in mice that express the wild-type human tau protein (htau mice). VLP exposure elicited dose-dependent changes in corticosterone and distinct chemokine levels. Longitudinal two-photon microscopy recordings of primary somatosensory and motor cortex neurons that express the jGCaMP7s calcium sensor tracked modifications of neuronal activity patterns following exposure to VLPs. There was a substantial short-term increase in stimulus-evoked activity metrics in both WT and htau VLP-injected mice, while htau mice showed also increased spontaneous activity metrics and increase activity in the vehicle-injected group. Over the following weeks, activity metrics in WT mice subsided, but remained above baseline levels. For htau mice, activity metrics either remain elevated or decreased to lower levels than baseline. Overall, our data suggest that exposure to the SARS-CoV-2 VLPs leads to strong short-term disruption of cortical activity patterns in mice with long-term residual effects. The htau mice, which have a more vulnerable genetic background, exhibited more severe pathobiology that may lead to more adverse outcomes.

Visuo-Vestibular Integration for Self-Motion: Human Cortical Area V6 Prefers Forward and Congruent Stimuli
BACKGROUND: The integration of visual and vestibular input is crucial for self-motion. Information from both sensory systems merges early in the central nervous system. Among the numerous cortical areas involved in processing this information, some (V6 and VIP) respond specifically to vestibular anteroposterior information. OBJECTIVE: To further understand the involvement of these and other areas in self-motion processing when vestibular and visual information are combined with varying congruence and direction parameters. METHODS: Fifteen subjects underwent an MRI session while receiving visual (optic flow patterns) and galvanic vestibular stimuli mimicking six conditions: (1) visual forward, (2) visual backward, visual forward with (3) congruent or (4) incongruent vestibular information, visual backward with (5) congruent or (6) incongruent vestibular information. RESULTS: The combination of concurrent vestibular stimulation and fully consistant optic flow patterns activated several bilateral cortical areas found predominantly in the insula. Among these vestibular areas and those previously defined in our initial study, the large majority do not show any specifity for the forward/backward direction or for the visuo-vestibular congruency. A notable exception was the parieto-occipital area V6, which showed a marked preference for congruent visuo-vestibular signals and for cues signaling forward motion. CONCLUSIONS: By showing that V6 is more active when visuo-vestibular signals are more ecological (i.e. when both signals specify the most common self-motion direction), our results support the view that this area plays a crucial role in visuo-vestibular integration during self-motion.

Pubertal hormones and the early adolescent female brain: a multimodality brain MRI study
Puberty is a critical developmental process that is associated with changes in steroid hormone levels, which are believed to influence adolescent behaviour via their effects on the developing brain. So far, there are limited and inconsistent findings regarding the relationship between steroid hormones and brain structure and function in adolescent females, with many existing studies employing small sample sizes. Thus, in this study, we explored the association between oestradiol (E2), testosterone (Tes) and dehydroepiandrosterone (DHEA) and brain structure (gray matter volume, sulcal depth, cortical thickness and white matter microstructure) and function (resting-state connectivity, emotional n-back task-related function) in 3024 adolescent females (age 8.92 - 13.33 years, mean age (SD) = 10.37 (0.94) years) from the Adolescent Brain Cognitive Development (ABCD) Study. We used elastic-net regression with cross-validation to investigate associations between hormones and brain phenotypes derived from multiple imaging modalities. We found that structural brain features, including cortical thickness, sulcal depth, and white matter microstructure, were among the most important features associated with hormones. E2 was most strongly associated with prefrontal and premotor regions involved in working memory and emotion processing, while Tes and DHEA were most strongly associated with parietal and occipital regions involved in visuospatial functioning. All three hormones were also associated with prefrontal, temporoparietal junction and insula cortices. Thus, using an advanced methodological approach, this study suggests both unique and overlapping neural correlates of pubertal hormones in adolescent females and sheds light on the mechanisms by which puberty influences adolescent development and behaviour.

Ciliopathy interacts with neonatal anesthesia to cause non-apoptotic caspase-mediated motor deficits
Increasing evidence suggests that anesthesia may induce developmental neurotoxicity, yet the influence of genetic predispositions associated with congenital anomalies on this toxicity remains largely unknown. Children with congenital heart disease often exhibit mutations in cilia-related genes and ciliary dysfunction, requiring sedation for their catheter or surgical interventions during the neonatal period. Here we demonstrate that briefly exposing ciliopathic neonatal mice to ketamine causes motor skill impairments, which are associated with a baseline deficit in neocortical layer V neuron apical spine density and their altered dynamics during motor learning.. These neuromorphological changes were linked to augmented non-apoptotic neuronal caspase activation. Neonatal caspase suppression rescued the spine density and motor deficits, confirming the requirement for sublethal caspase signaling in appropriate spine formation and motor learning. Our findings suggest that ciliopathy interacts with ketamine to induce motor impairments, which is reversible through caspase inhibition. Furthermore, they underscore the potential for ketamine-induced sublethal caspase responses in shaping neurodevelopmental outcomes.

Distinguishing the activity of adjacent somatosensory nuclei within the brainstem using 3T fMRI
Experimental evidence in animal models indicates that the brainstem plays a major role in sensory modulation. However, mapping functional activity within the human brainstem presents many methodological challenges. These constraints have deterred essential research into human sensory brainstem processing. Here, using a 3T fMRI sequence optimised for the brainstem, combined with uni- and multivariate analysis approaches, we investigated the extent to which functional activity of neighbouring somatosensory nuclei can be delineated in the brainstem, thalamus and primary somatosensory cortex (S1). Whilst traditional univariate approaches offered limited differentiation between adjacent hand and face activation in the brainstem, multivariate classification enabled above-chance decoding of these activity patterns across S1, the thalamus, and the brainstem. Our findings establish a robust methodological approach to explore signal processing within the brainstem and across the entire somatosensory stream. This is a fundamental step towards broadening our understanding of somatosensory processing within humans and determining what changes in sensory integration may occur in clinical populations following sensory deprivation.

Disordered Hippocampal Reactivations Predict Spatial Memory Deficits in a Mouse Model of Alzheimer's Disease
Alzheimer's disease (AD) is characterised by progressive memory decline associated with hippocampal degeneration. However, the specific physiological mechanisms underlying hippocampal dysfunction in AD remain poorly understood and improved knowledge may aid both diagnosis and help identify new avenues for therapeutic intervention. We investigated how disruptions in hippocampal reactivations relate to place cell stability and spatial memory deficits in an AD mouse model. Using the APP knock-in mouse model 'NL-G-F', we conducted simultaneous behavioural and electrophysiological recordings in a radial arm maze. NL-G-F mice exhibited significant impairments in memory performance, demonstrated by an increased propensity to revisit arms, compared to wild-type controls. These memory deficits were associated with a reduction in the stability of hippocampal place cells, which occurred over short timescales and was accentuated across rest. While the rate of hippocampal reactivation events during rest was unchanged, the structure of these events was significantly degraded in NL-G-F mice. The decreased structure of reactivations was predictive of decreased stability in place cell firing. These findings suggest that disrupted reactivation sequences may act as a mechanism of memory disorder in AD.

The effect of prolonged elbow pain and rTMS on cortical inhibition: A TMS-EEG study
IntroductionRecent studies using combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) have shown that pain leads to an increase in the N45 peak of the TMS-evoked potential (TEP), which is mediated by GABAergic inhibition. Conversely, 10Hz repetitive TMS (10Hz-rTMS), which provides pain relief, reduces the N45 peak. However, these studies used brief pain stimuli (lasting minutes), limiting their clinical relevance. The present study determined the effect of pain and 10Hz-rTMS on the N45 peak in a prolonged pain model (lasting several days) induced by nerve growth factor (NGF) injection to the elbow muscle.

Materials and MethodsExperiment 1: TEPs were measured in 22 healthy participants on Day 0 (pre-NGF), Day 2 (peak pain), and Day 7 (pain resolution). Experiment 2: We examined the effect of 5 days of active (n=16) or sham (n=16) rTMS to the left primary motor cortex (M1) on the N45 peak during prolonged NGF-induced pain, with TEPs measured on Day 0 and Day 4 (post-rTMS).

ResultsExperiment 1: While no overall change in the N45 peak was seen, a correlation emerged between higher pain severity on Day 2 and a larger increase in the N45 peak.

Experiment 2: Active rTMS reduced the N45 peak on Day 4 vs. Day 0, with no effect in the sham group.

ConclusionOur findings suggest that (i) higher pain severity correlates with an increase in the N45 peak, and (ii) rTMS decreases cortical inhibition in a model of prolonged experimental pain. This study extends previous research by demonstrating a link between pain perception and cortical inhibition within a prolonged pain context.

Circuit mechanisms underlying sexually dimorphic outcomes of early life stress
Stress during early life influences brain development and can affect social, motor, and emotional processes. We describe a striking sex difference in the effects of early life stress (ELS), which produces anhedonia and anxiety-like behaviors in female adolescent mice, as reported previously, but repetitive behavioral pathology and social deficits in male adolescent mice. Notably, this parallels sex differences seen in the prevalence of psychiatric symptoms: depression and anxiety disorders are more common in girls and women, whereas neurodevelopmental disorders like autism spectrum disorder and Tourette syndrome are markedly more common in boys and men. We characterized the effects of ELS on the medial prefrontal cortex (mPFC) and on its projections to the dorsal striatum (dStr) and lateral septum (LS). ELS males, but not females, developed hyperactivity in the cortico-striatal circuit and hypoactivity in the cortico-septal circuit. Chemogenetic manipulation of cortico-striatal projection neurons modulates repetitive behavioral pathology and social behaviors in stressed males, and anhedonia in stressed females. Activation of cortico-septal projection neurons rescues social deficits in stressed males. We conclude that early life stress produces sexually dimorphic behavioral effects, with potential relevance to human psychiatric symptoms, through its differential effects on cortico-striatal and cortico-septal circuits.

Covert muscle activity reveals dynamic freezing states and prepares the animal for action
When an animal detects a threat it must make a split-second choice between fight, flight or freezing (1-3). During freezing, skeletal muscles sustain tension to maintain rigid, sometimes atypical postures, for many minutes at a time (4). Meanwhile the animal must dynamically assess its surroundings to plan future actions and ready its body for movement. The interplay between the neural and somatic systems during freezing remains poorly understood. Here we show that freezing Drosophila melanogaster display a striking novel pattern of leg muscle activation unique to immobility, a rhythmic pulsing in the distal tibia. The muscle, which we show to be a previously undescribed leg accessory heart, displays multiple activity modes and ramps up to movement onset, implying a preparation for movement. The frequency of pulsing is dynamically modulated as the fly integrates external threat or safety cues, and artificially increasing pulse frequency leads to freezing breaks, indicating a causal role in the decision to move. Through the identification of a new Drosophila cardiac organ, this study provides a window into the multiple states which can underlie freezing behaviour, and the physiological changes which the body undergoes to ready the animal to move.

Dorsolateral prefrontal cortex drives strategic aborting by optimizing long-run policy extraction
Real world choices often involve balancing decisions that are optimized for the short- vs. long-term. Here, we reason that apparently sub-optimal single trial decisions in macaques may in fact reflect long-term, strategic planning. We demonstrate that macaques freely navigating in VR for sequentially presented targets will strategically abort offers, forgoing more immediate rewards on individual trials to maximize session-long returns. This behavior is highly specific to the individual, demonstrating that macaques reason about their own long-run performance. Reinforcement-learning (RL) models suggest this behavior is algorithmically supported by modular actor-critic networks with a policy module not only optimizing long-term value functions, but also informed of specific state-action values allowing for rapid policy optimization. The behavior of artificial networks suggests that changes in policy for a matched offer ought to be evident as soon as offers are made, even if the aborting behavior occurs much later. We confirm this prediction by demonstrating that single units and population dynamics in macaque dorsolateral prefrontal cortex (dlPFC), but not parietal area 7a or dorsomedial superior temporal area (MSTd), reflect the upcoming reward-maximizing aborting behavior upon offer presentation. These results cast dlPFC as a specialized policy module, and stand in contrast to recent work demonstrating the distributed and recurrent nature of belief-networks.

An automatic domain-general error signal is shared across tasks and predicts confidence in different sensory modalities
Understanding the ability to self-evaluate decisions is an active area of research. This research has primarily focused on the neural correlates of self-evaluation during visual-tasks, and whether pre- or post-decisional neural correlates capture subjective confidence in that decision. This focus has been useful, yet also precludes an investigation of key every-day features of metacognitive self-evaluation: that decisions are rapid, must be evaluated without explicit feedback, and unfold in a multisensory world. These considerations lead us to hypothesise that an automatic domain-general metacognitive signal may be shared between sensory modalities, which we tested in the present study with multivariate decoding of electroencephalographic (EEG) data. Participants (N=21, 12 female) first performed a visual task with no request for self-evaluations of performance, prior to an auditory task that included rating decision confidence on each trial. A multivariate classifier trained to predict errors in the speeded visual-task generalised to predict errors in the subsequent non-speeded auditory discrimination. This generalisation was unique to classifiers trained on the visual response-locked data, and further predicted subjective confidence on the subsequent auditory task. This evidence of overlapping neural activity across the two tasks provides evidence for automatic encoding of confidence independent of any explicit request for metacognitive reports, and a shared basis for metacognitive evaluations across sensory modalities.

Hunger alters approach-avoidance behaviours differently in male and female mice
BackgroundThe decision about whether to approach or avoid a reward while under threat requires balancing competing demands. Sex-specific prioritisations (e.g. mating, maternal care), or generalised prioritisations (e.g. feeding, drinking, sleeping) may differently influence approach-avoidance behaviours based on the level of "risk" and homeostatic need state of the organism. However, given known sex differences in key aspects that may influence this behaviour, direct comparison of how male and female mice make decisions to approach or avoid a dangerous area while in a fasted state have yet to be conducted.

MethodsWe conducted several approach-avoidance tasks with varied levels of risk and reward in male and female mice that were either fasted or sated (fed). Mice underwent a light-dark box, elevated plus maze, baited large open field and runway task to assess their approach and avoidance behaviour.

ResultIn the light-dark box and elevated plus maze, when no reward was available, fasted female mice showed greater approach behaviours than male counterparts. In the baited large open field, when reward was available, both sexes showed increased approach behaviours when fasted. However, when sated, male mice conversely showed greater approach behaviours compared to sated female mice. In the runway task, while sated mice failed to learn, fasted male mice inhibited their reward consumption in response to increased shock intensity; however, fasted female mice were resistant to increased shock intensity.

ConclusionsOur study identifies sex differences in decision making behaviour in mice based on satiety state across a number of approach-avoidance tasks. We highlight several nuances of these differences based on reward availability and punishment intensity. These results shine a lens on fundamental differences between the sexes in innate, survival driven behaviours that should be taken into account for future studies.

Plain English summaryEveryday decision making is often accompanied by conflict - whether we make the most appropriate decision or not can be influenced by both internal and external factors. Environmental threats and physiological pressures, such as hunger, can influence decision-making processes skewing the risk/reward ratio, yet how this may differ between the sexes has not been explored in detail. Here we used several tasks that assess decision-making in mice while manipulating the levels of risk or reward. Our findings show fasted female mice are more willing to engage in "risky" behaviour compared to fed female mice when risk levels were low, and no food reward was available. However, when a food reward was available, but risk levels were low, both male and female fasted mice were more likely to engage in risky behaviour compared to fed mice. Finally, when risk levels were high and food reward was available, fasted female mice continued to engage in risky behaviour, while male fasted mice were not. Together our study identifies nuanced sex differences in how male and female mice make decisions influenced by both physiological (hunger) and environmental threats and highlight the importance of understanding fundamental differences between the sexes in behaviour.

Highlights- Fasted female mice showed greater approach behaviours compared to fasted male counterparts in tasks without reward availability.
- Fasted mice of both sexes displayed greater approach behaviours when a reward was available, compared to sated controls.
- Fasted male mice inhibited reward consumption under increased shock intensity, whereas fasted female mice were resistant to mild foot shock.

Assessing the feasibility of a new approach to measure the full spectrum of CSF dynamics within the human brain using MRI: insights from a simulation study
Cerebrospinal fluid (CSF) dynamics are essential in waste clearance of the brain. Disruptions in CSF flow are linked to various neurological conditions, highlighting the need for accurate measurement of its dynamics. Current methods typically capture limited aspects of CSF movement or focus on a single anatomical region, presenting challenges for comprehensive analysis. This study proposes a novel approach using Displacement Encoding with Stimulated Echoes (DENSE) MRI to assess the full spectrum of CSF motion within the brain. Through simulations, we evaluated the feasibility of disentangling distinct CSF motion components, including heartbeat- and respiration-driven flows, as well as a net velocity component due to continuous CSF turnover, and tested the performance of our method under incorrect assumptions about the underlying model of CSF motion. Results demonstrate that DENSE MRI can accurately separate these components, and reliably estimated a net velocity, even when periodic physiological motions vary over time. The method proved to be robust for including low frequency components (LFO), incorrect assumption on the nature of the net velocity component and missing CSF components in the model. This approach offers a comprehensive measurement technique for quantifying CSF dynamics, advancing our understanding of the relative role of various drivers of CSF dynamics in brain clearance.

Gustatory sensitivity to amino acids in bumblebees
Bees rely on amino acids obtained from nectar and pollen for essential physiological functions, including maintenance, sexual maturation, and larval development. While amino acid concentrations in nectar are typically low (<1 mM), pollen contains higher levels (10-200 mM), with the exact concentrations varying by plant species. Behavioural studies suggest bumblebees have preferences for specific amino acids, yet whether such preferences are mediated pre-ingestively via gustatory mechanisms remains unclear. This study explores bumblebees (Bombus terrestris) gustatory sensitivity to two essential amino acids (EAAs), valine and lysine, using electrophysiological recordings from gustatory sensilla on their mouthparts. Valine elicited a concentration-dependent response, with spikes produced from 0.1 mM and reaching an asymptote at 5 mM, indicating that bumblebees could perceive valine at the concentrations found naturally in nectar and pollen. In contrast, lysine failed to evoke spiking responses across tested concentrations (0.1-500 mM). The absence of lysine detection raises questions about the specificity and diversity of amino acid-sensitive receptors in bumblebees. Bees responded to valine at lower concentrations than sucrose, suggesting comparatively higher sensitivity to amino acids (EC50: 0.7 mM vs. 3.91 mM for sucrose). Our findings indicate that bumblebees are able to rapidly evaluate the amino acid content of pollen and nectar while foraging from flowers using pre-ingestive cues, rather than relying on post-ingestive cues or feedback from their nestmates. Such sensory capabilities likely impact foraging strategies, with implications for plant-bee interactions and pollination. Future research should explore bumblebees response to other amino acids in isolation and combination, and mechanisms for detecting pollen-bound nutrients.

Functional maturation and experience-dependent plasticity in adult-born olfactory bulb dopaminergic neurons
Continued integration of new neurons persists in only a few areas of the adult mouse brain. In the olfactory bulb (OB), immature adult-born neurons respond differently to olfactory stimuli compared to their more mature counterparts, and have heightened levels of activity-dependent plasticity. These distinct functional features are thought to bestow unique properties onto existing circuitry. OB interneurons, including those generated through adult neurogenesis, consist of a set of highly distinct subtypes. However, we do not currently know the different cell-type-specific mechanisms underlying their functional development and plastic potential. Here, we specifically characterised electrophysiological maturation and experience-dependent plasticity in a single, defined subtype of adult-born OB neuron: dopaminergic cells. We selectively live-labelled both adult-born and resident dopaminergic cells, and targeted them for whole-cell patch-clamp recordings in acute mouse OB slices. Surprisingly, we found that from the time - at [~]1 month of cell age - that live adult-born dopaminergic neurons could first be reliably identified, they already possessed almost fully mature intrinsic firing properties. We saw significant maturation only in increased spontaneous activity and decreased medium afterhyperpolarisation amplitude. Nor were adult-born dopaminergic cells especially plastic. In response to brief sensory deprivation via unilateral naris occlusion we observed no maturation-specific plastic alterations in intrinsic properties, although we did see deprivation-associated increases in spike speed and amplitude across all adult-born and resident neurons. Our results not only show that adult-born OB dopaminergic cells rapidly functionally resemble their pre-existing counterparts, but also underscore the importance of subtype identity when describing neuronal maturation and plasticity.

Synergistic Behavioral and Neuroplastic Effects of Psilocybin-NMDAR Modulator Administration.
The full therapeutic potential of serotonergic psychedelics (SP) in treating neuropsychiatric disorders, such as depression and schizophrenia, is limited by possible adverse effects, including perceptual disturbances and psychosis, which require administration in controlled clinical environments. This study investigates the synergistic benefits of combining psilocybin (PSIL) with N-methyl-D-aspartate receptor (NMDAR) modulators D-serine (DSER) and D-cycloserine (DCS) to enhance both efficacy and safety. Using ICR male mice, we examined head twitch response (HTR), MK-801-induced hyperlocomotion, and neuroplasticity related synaptic protein levels in the frontal cortex, hippocampus, amygdala, and striatum. Our results indicate that PSIL significantly increased HTR--a surrogate measure for hallucinogenic effects--which was reduced by the co-administration of DSER or DCS in a dose-dependent manner. Similarly, combining PSIL with DSER or DCS significantly decreased MK-801-induced hyperactivity, modeling antipsychotic effects. Neuroplasticity-related synaptic protein assays demonstrated that the PSIL-DSER combination enhanced GAP43 expression over all 4 brain examined and overall expression of the 4 assayed synaptic proteins in the hippocampus, while PSIL-DCS elevated PSD95 levels across all 4 brain regions, suggesting a synaptogenic synergy. These findings support the hypothesis that combinations of SP with NMDAR modulators could optimize the therapeutic potential of SP by mitigating adverse effects and enhancing neuroplasticity. Future studies should focus on refining administration protocols and evaluating translational applicability for broader clinical use.

The role of cholinergic signaling in multi-sensory gamma stimulation induced perivascular clearance of amyloid
Modulatory neurotransmitters exert powerful control over neurons and the brain vasculature. Gamma Entrainment Using Sensory Stimuli (GENUS) promotes amyloid clearance via increased perivascular cerebral spinal fluid (CSF) flux in mouse models of Alzheimers Disease. Here we use whole-brain activity mapping to identify the cholinergic basal forebrain as a key region responding to GENUS. In line with this, GENUS promoted cortical acetylcholine release, vascular dilation, vasomotion and perivascular clearance. Inhibiting cholinergic signaling abolished the effects of GENUS, including the promotion of arterial pulsatility, periarterial CSF influx, and the reduction of cortical amyloid levels. Our findings establish cholinergic signaling as an essential component of the brains ability to promote perivascular amyloid clearance via non-invasive sensory stimulation.