bioRxiv Subject Collection: Neuroscience's Journal

Spatial Expression of Long Non-Coding RNAs in Human Brains of Alzheimer's Disease
Long non-coding RNAs (lncRNAs) are highly versatile in their modes of action and play critical roles in both normal physiological and disease processes. The dysregulation of lncRNA expression has been implicated in aging and many neurological disorders, including Alzheimer's disease (AD). Here, we report a spatial expression atlas of 7,634 lncRNA genes in aged human brains, covering 258,987 microdomains from 78 postmortem brain sections of 21 ROSMAP participants. We detected a greater proportion of lncRNAs expressed specifically in distinct cortical subregions than mRNAs, and most belong to antisense and lincRNA biotypes. We generated 193 gene modules from gene networks of 8 subregions and identified lncRNA-enriched gene modules implicated in multiple AD-relevant biological processes. By cross-referencing published snRNA-seq data, we detected a partially overlapping but independent pattern between sub-region and cell-type specificity of lncRNA expression. We mapped spatially differentially expressed (SDE) lncRNAs and mRNAs in AD brains and observed that SDE lncRNAs encompass more subregion-specific transcripts. Gene set enrichment analysis indicates that AD SDE lncRNAs are involved in epigenetic regulation, chromatin remodeling, RNA metabolism, synaptic signaling, and apoptosis. Particularly relevant to AD therapeutic potentials is an enrichment for HDAC target genes, including OIP5-AS1, a lncRNA extensively studied in cancer and, most recently, in AD. We then applied multivariate fine-mapping to the expression quantitative trait loci (eQTLs) proximal to the OIP5-AS1 loci and identified rs1655558 as a potential genetic driver of OIP5-AS1 expression. Using statistical modeling, we inferred that the interaction between OIP5-AS1 and HDAC proteins, especially HDAC11, is associated with tau tangles in excitatory neurons and plaque burden in microglia. Our study represents a valuable resource of lncRNA spatial expression in the aged human brain, shedding mechanistic insights into their functional roles in AD and neurodegeneration.

Effect of digital noise-reduction processing on subcortical speech encoding and relationship to behavioral outcomes
Perceptual benefits from digital noise reduction (NR) vary among individuals with different noise tolerance and sensitivity to distortions introduced in NR-processed speech; however, the physiological bases of the variance are understudied. Here, we developed objective measures of speech encoding in the ascending pathway as candidate measures of individual noise tolerance and sensitivity to NR-processed speech using the brainstem responses to speech syllable /da/. The speech-evoked brainstem response was found to be sensitive to the addition of noise and NR processing. The NR effects on the consonant and vowel portion of the responses were robustly quantified using response-to-response correlation metrics and spectral amplitude ratios, respectively. Further, the f0 amplitude ratios between conditions correlated with behavioral accuracy with NR. These findings suggest that investigating the NR effects on bottom-up speech encoding using brainstem measures is feasible and that individual subcortical encoding of NR-processed speech may relate to individual behavioral outcomes with NR.

The influence of temporal context on vision over multiple time scales
Past sensory experiences influence perception of the present. Multiple research subfields have emerged to study this phenomenon at different temporal scales. These fall into three categories: the influence of immediately preceding sensory events (micro), short sequences of events (meso), and regularities over long sequences of events (macro). In a single paradigm, we examined the influence of temporal context on perception at each scale. We identify two distinct mechanisms that operate across all scales. The first is moderated by attention and supports rapid motor responses to expected events. The second is independent of task-demands and dampens the feedforward neural responses to expected events, leading to unexpected events eliciting earlier and more precise neural representations. We further show that perceptual recall exclusively reflects neural representations during this initial feedforward stage and that serial dependence (recall biases towards previous events) is explained by expectation of sensory stability over time.

Alzheimer's Disease Patient Brain Extracts Induce Multiple Pathologies in Vascularized Neuroimmune Organoids for Disease Modeling and Drug Discovery
Alzheimer's Disease (AD) is the most common cause of dementia afflicting 55 million individuals worldwide, with limited treatment available. Current AD models mainly focus on familial AD (fAD), which is due to genetic mutations. However, models for studying sporadic AD (sAD), which represents over 95% of AD cases without specific genetic mutations, are severely limited. Moreover, the fundamental species differences between humans and animals might significantly contribute to clinical failures for AD therapeutics that have shown success in animal models, highlighting the urgency to develop more translational human models for studying AD, particularly sAD. In this study, we developed a complex human pluripotent stem cell (hPSC)-based vascularized neuroimmune organoid model, which contains multiple cell types affected in human AD brains, including human neurons, microglia, astrocytes, and blood vessels. Importantly, we demonstrated that brain extracts from individuals with sAD can effectively induce multiple AD pathologies in organoids four weeks post-exposure, including amyloid beta (A{beta}) plaques-like aggregates, tau tangles-like aggregates, neuroinflammation, elevated microglial synaptic pruning, synapse/neuronal loss, and impaired neural network. Furthermore, after treatment with Lecanemab, an FDA-approved drug targeting A{beta}, AD brain extract exposed organoids showed a significant reduction of amyloid burden. Thus, the neuroimmune organoid model provides a unique opportunity to study AD, particularly sAD under a pathophysiological relevant three-dimensional (3D) human cell environment. It also holds great promise to facilitate AD drug development, particularly for immunotherapies.

Levetiracetam prevents Aβ42 production through SV2a-dependent modulation of App processing in Alzheimer's disease models
In Alzheimers disease (AD), amyloid-beta (A{beta}) peptides are produced by proteolytic cleavage of the amyloid precursor protein (APP), which can occur during synaptic vesicle (SV) cycling at presynapses. Precisely how amyloidogenic APP processing may impair presynaptic proteostasis and how to therapeutically target this process remains poorly understood. Using App knock-in mouse models of early A{beta} pathology, we found proteins with hampered degradation accumulate at presynaptic sites. At this mild pathological stage, amyloidogenic processing leads to accumulation of A{beta}42 inside SVs. To explore if targeting SVs modulates A{beta}42 accumulation, we investigated levetiracetam (Lev), a SV-binding small molecule drug that has shown promise in mitigating AD-related pathologies despite its mechanism of action being unclear. We discovered Lev reduces A{beta}42 levels by decreasing amyloidogenic processing of APP in a SV2a-dependent manner. Lev corrects SV protein levels and cycling, which results in increased surface localization of APP, where it favors processing via the non-amyloidogenic pathway. Using metabolic stable isotopes and mass spectrometry we confirmed that Lev prevents the production of A{beta}42 in vivo. In transgenic mice with aggressive pathology, electrophysiological and immunofluorescent microscopy analyses revealed that Lev treatment reduces SV cycling and minimizes synapse loss. Finally, we found that human Down syndrome brains with early A{beta} pathology, have elevated levels of presynaptic proteins, confirming a comparable presynaptic deficit in human brains. Taken together, we report a mechanism that highlights the therapeutic potential of Lev to modify the early stages of AD and represent a promising strategy to prevent A{beta}42 pathology before irreversible damage occurs.

NAD+ - and EVA1-C-dependent reversal of neurological deficits is mediated by differential alternative RNA splicing in tauopathic animal models
Aberrant alternative splicing events (ASEs) are emerging as a new hallmark of aging and are linked to age-related neurodegenerative pathologies such as Alzheimer's disease (AD). AD brains are characterized by abundant intracellular proteinaceous aggregates, including neurofibrillary tangles (NFTs). Although NAD+ and related metabolites can slow down AD progression, the effects of NAD+ on ASEs in AD remain unclear. This study investigates the relationships between NAD+ metabolism, ASEs and AD or AD-like pathologies including tauopathies using deep-learning AI-based algorithms to predict protein structures and protein-protein interactions as well as experimental tauopathy models including hTau.P301S transgenic mice and transgenic hTau[P301L] Caenorhabditis elegans. Mouse transcriptomic data were mined to detect ASEs that were differentially induced in the presence of NAD+ precursor nicotinamide riboside (NR) with specific focus on the Eva1-C locus. The results reveal that the relative abundance of Eva1-C isoforms is sensitive to both the concentration of NR and to tauopathy genotype. NAD+ abundance/metabolic status modulates ASEs and the expression of EVA1-C isoforms, which in turn regulate the interaction with the key proteins, BAG-1 and HSP70, involved in orchestrating protein homeostasis. Importantly, EVA1-C is dramatically reduced in the postmortem entorhinal cortex and hippocampal neurons from 20 Braak 5/6 AD patients compared to 20 of cognitive normal humans. Thus, this study supports the novel idea that NAD+ metabolism modulates abundance of specific mRNA isoforms, and that ASEs influence disease progression in model tauopathies and potentially AD. These results could facilitate future development of NAD+-based splice-switching therapeutics for AD.

The Role of Physical Activity in Mitigating Age-Related Changes in the Neuromuscular Control of Gait
Exercise is known to induce several neural and muscular adaptations, such as increased muscle mass and functional capacity in older adults. In this study, we investigated its impact on the neuromuscular control of gait among young and older adults, divided into two groups: more active (young: n=15; 5185 +- 1471 MET-min/week; old: n=14; 6481 +- 4846 MET-min/week) and less active participants (young: n=14; 1265 +- 965 MET-min/week; old: n=14; 1473 +- 859 MET-min/week). Maximal isometric tests of ankle and knee extension revealed a reduction in force among older adults, with differences associated with the level of physical activity at the ankle level. Gait mechanics revealed no significant differences between young adults and the more active older adults. In contrast, less active older adults exhibited shorter steps, higher mechanical cost, and greater collision at heel strike. These changes cannot be attributed solely to reductions in muscle strength. Instead, they are likely the result of modifications in neuromuscular control and mechanical properties of muscles in less active older adults. Specifically, wider activation (and greater coactivation) of lumbar and sacral motor pools as well as a different timing of activation were observed. Also, their muscle-tendon stiffness was reduced. In conclusion, our findings highlight that the age-related decline in gait efficiency is exacerbated by a sedentary lifestyle. Even modest increases in physical activity appear to preserve neuromuscular control and improve walking performance. This suggests that interventions aiming to enhance physical activity levels could mitigate age-related declines in gait mechanics.

A circuit model for transsaccadic space updating and mislocalization
We perceive a stable, continuous world despite drastic changes of retinal images across saccades. However, while persistent objects in daily life appear stable across saccades, stimuli flashed around saccades can be grossly mislocalized. We address this puzzle with our recently proposed circuit model for perisaccadic receptive-field (RF) remapping in LIP and FEF. The model uses center/surround connections to store a relevant stimulus' retinal location in memory as a population activity. This activity profile is updated across each saccade by directional connections gated by the corollary discharge (CD) of the saccade command. The updating is a continuous backward (against the saccade) shift of the population activity (equivalent to continuous forward remapping of the RFs), whose cumulative effect across the saccade is a subtraction of the saccade vector. The model explains forward and backward translational mislocalization for stimuli flashed around the saccade onset and offset, respectively, as insufficient and unnecessary cumulative updating after the saccade, caused by the sluggish CD time course and visual response latency. We confirm the model prediction that for perisaccadic RFs measured with flashes before the saccades, the final forward remapping magnitudes after the saccades are smaller for later flashes. We discuss the possibility that compressive mislocalization results from a brief reduction of attentional remapping and repulsion. Although many models of RF remapping, transsaccadic updating, and perisaccadic mislocalization have been proposed, our work unifies them into a single circuit mechanism and suggests that the brain uses "unaware" decoders which do not distinguish between different origins of neurons' activities.

Orthogonal spectral and temporal envelope representation in auditory cortex
Speech sounds are acoustically composed of two main components: spectral and temporal. The spectral components or carrier frequency is known to be perceived through activity at specific locations on the tonotopic map in the auditory cortex. The temporal envelope - referring to the dynamic changes in sound wave amplitude over time - plays an essential role in speech perception by mediating phoneme recognition. However, how the steepness of the envelope, which shapes its temporal structure, is represented in the auditory cortex remains poorly understood. This study investigates how the steepness of the envelope of sound waves is represented as a functional organization in the mouse auditory cortex, in relation to spectral tonotopic organization. Using macroscale calcium imaging in GCaMP6f-expressing mice, we mapped the auditory cortex's responses to tones with systematically varying rise-ramp steepness and frequencies. Our findings reveal that, in two primary-like regions of the auditory cortex, the steepness of the rise ramp is orderly mapped orthogonally to the tonotopic gradient, forming a two-dimensional representation on the cortical surface. Conversely, a significant representation of rise-ramp steepness was not detected in higher-order-like auditory regions. These findings suggest that a dichotomous functional organization independently processes temporal envelopes and spectral features in the mammalian auditory cortex, with cortical functional structures mirroring the two acoustic structures.

Synaptic composition, activity, mRNA translation and dynamics in combined single-synapse profiling using multimodal imaging
The function of neuronal circuits, and its perturbation by psychoactive molecules or disease-associated genetic variants, is governed by the interplay between synapse activity and synaptic protein localization and synthesis across a heterogeneous synapse population. Here, we combine in situ measurement of synaptic multiprotein compositions and activation states, synapse activity in calcium traces or glutamate spiking, and local translation of specific genes, across the same individual synapses. We demonstrate how this high-dimensional data enables identification of interdependencies in the multiprotein-activity network, and causal dissection of complex synaptic phenotypes in disease-relevant chemical and genetic NMDAR loss of function that translate in vivo. We show how this method generalizes to other subcellular systems by deriving mitochondrial protein networks, and, using support vector machines, its value in overcoming animal variability in phenotyping. Integrating multiple synapse information modalities enables deep structure-function characterization of synapse populations and their responses to genetic and chemical perturbations.

Acute Aerobic Exercise Enhances Associative Learning in Active but not Sedentary Individuals
Physical exercise has repeatedly been reported to have advantageous effects on brain functions, including learning and memory formation. However, objective tools to measure such effects are often lacking. Eyeblink conditioning is a well-characterised method for studying the neural basis of associative learning. As such, this paradigm has potential as a tool to assess to what extent exercise affects one of the most basic forms of learning. Until recently, however, using this paradigm for testing human subjects in their daily life was technically challenging. As a consequence, no studies have investigated how exercise affects eyeblink conditioning in humans. Here we hypothesize that acute aerobic exercise is associated with improved performance in eyeblink conditioning. Furthermore, we explored whether the effects of exercise differed for people with an active versus a sedentary lifestyle. We conducted a case-control study using a smartphone-based platform for conducting neurometric eyeblink conditioning in healthy adults aged between 18-40 years (n = 36). Groups were matched on age, sex, and education level. Our primary outcome measures included the amplitude and timing of conditioned eyelid responses over the course of eyeblink training. As a secondary measure, we studied the amplitude of the unconditioned responses. Acute exercise significantly enhanced the acquisition of conditioned eyelid responses; however, this effect was only true for individuals with an active lifestyle. No statistically significant effects were established for timing of the conditioned responses and amplitude of the unconditioned responses. This study highlights a facilitative role of acute aerobic exercise in associative learning and emphasises the importance of accounting for lifestyle when investigating the acute effects of exercise on brain functioning.

Chemosensory modulation of eye-body coordination in larval zebrafish
Coordinated eye-body movements are essential for many animal behaviors, yet the influence of chemosensory inputs on these movements remains underexplored. Here, we enhance the Fish-On-Chips optofluidic platform to reveal that larval zebrafish use coupled saccade-tail flips for chemosensory avoidance, but not pursuit. Spontaneous saccades, which alternate in direction, are closely synchronized with tail flips via anticipatory adjustments in tail flip event rate, directionality, and kinematics. In response to ethologically representative chemosensory cues, this coordination is differentially modulated based on valence. Aversive chemical cues increase saccade frequency and the proportion of saccade-coupled tail flips, while also enhancing the turning intent as the coupling strengthens. Conversely, appetitive chemicals promote more sustained gliding movements without impacting saccades or their tail flip coupling. Brain-wide neuronal activity imaging reveals that the pallium, a cortical homolog in teleosts, strongly represents the sensorimotor transformation of aversive cue-associated coupled saccade tail flips. Our findings underscore the critical role of chemosensory cues in regulating eye-body coordination in an early vertebrate species, highlighting a deep evolutionary integration of sensory inputs to optimize locomotion.

Restoring the Multiple Sclerosis Associated Imbalance of Gut Indole Metabolites Promotes Remyelination and Suppresses Neuroinflammation
In multiple sclerosis (MS) the circulating metabolome is dysregulated, with indole lactate (ILA) being one of the most significantly reduced metabolites. We demonstrate that oral supplementation of ILA impacts key MS disease processes in two preclinical models. ILA reduces neuroinflammation by dampening immune cell activation/ infiltration; and promotes remyelination and in vitro oligodendrocyte differentiation through the aryl hydrocarbon receptor (AhR). Supplementation of ILA, a reductive indole metabolite, restores the gut microbiome's oxidative/reductive metabolic balance by lowering circulating indole acetate (IAA), an oxidative indole metabolite, that blocks remyelination and oligodendrocyte maturation. The ILA-induced reduction in circulating IAA is linked to changes in IAA-producing gut microbiota taxa and pathways that are also dysregulated in MS. Notably, a lower ILA:IAA ratio correlates with worse MS outcomes. Overall, these findings identify ILA as a new potential anti-inflammatory remyelinating agent and provide novel insights into the role of gut dysbiosis-related metabolic alterations in MS progression.

Neural field theory as a framework for modeling and understanding consciousness states in the brain
Understanding the neural correlates of consciousness remains a central challenge in neuroscience. In this study, we explore the potential of neural field theory (NFT) as a computational framework for representing consciousness states. While prior research has validated NFT's capacity to differentiate between normal and pathological states of consciousness, the relationship of its parameters to the representation of consciousness levels remains unclear. Here, we fitted a corticothalamic NFT model to EEG data collected from healthy individuals and patients with disorders of consciousness. We then comprehensively explored the correlations between the fitted NFT parameters and features extracted from both experimental and simulated EEG data, across various states of consciousness. The identified correlations not only highlight the model's ability to differentiate between states of consciousness, but also shed light on the physiological bases of these states, pinpointing potential biomarkers. Our results provide valuable insights into how consciousness levels are represented within the NFT framework and into the dynamics of brain activity across various consciousness states. This underscores the potential of NFT as a useful tool for consciousness research, facilitating in-silico experimentation.

Slow-wave sleep is associated with nucleus accumbens volume in elderly adults
Slow-wave sleep (SWS) is essential for restorative neural processes, and its decline is associated with both healthy and pathological ageing. Building on previous rodent research, this longitudinal study identified a significant association between nucleus accumbens (NAcc) volume and SWS duration in cognitively unimpaired older adults. Our findings support the involvement of the NAcc in ageing-related modulation of SWS and suggest potential therapeutic targets for improving SWS.

Minimally invasive electrocorticography (ECoG) recording in common marmosets
Electrocorticography (ECoG) enables high spatio-temporal resolution recordings of brain activity with excellent signal quality, making it essential for pre-surgical mapping in epilepsy patients and increasingly useful in neuroscience research, including the development of brain-machine interfaces. The relatively minimal cortical convolution in non-human primate (NHP) brains facilitates ECoG recordings, in particular in the common marmoset (Callithrix jacchus), whose lissencephalic (unfolded) brain surface provides broad cortical access. One of the key advantages of ECoG recordings is the ability to study interactions between distant brain regions. The standard approach is the usage of large electrode arrays, which, however, require extended trepanations and a trade-off between size and electrode spacing. This study introduces an alternative ECoG approach for examining interactions between multiple distant cortical areas in marmosets, combining the advantages of circumscribed trepanations with high-density electrode arrays at specific sites of interest. Two adult marmosets underwent ECoG implantation across frontal, temporal, and parietal regions of interest, assessed by circumscribed trepanations to position individual high-density electrode arrays. Postoperative monitoring showed rapid recovery and no long-term complications. The animals remained healthy, and stable neural recordings were successfully obtained during behavioral tasks, highlighting the method's effectiveness for long-term cortical monitoring.

Mapping hippocampal-cerebellar functional connectivity across the adult lifespan
Although the hippocampus and cerebellum are traditionally considered to support distinct memory systems, evidence from nonhuman species indicates a close bidirectional relationship during learning and navigational behaviour, with the hippocampus projecting to - and receiving input from - several cerebellar regions. However, little is known about the nature and topography of hippocampal-cerebellar connectivity in the human brain. To address this gap, we applied seed-based functional connectivity analyses to resting-state fMRI data from 479 cognitively normal participants, aged 18-88 years. We identified significant functional correlations between the hippocampus and widespread areas of cerebellar cortex, particularly lobules HIV, HV, HVI, HVIIA (Crus I and II), HIX, and HX. Contrasting the left and right hippocampus, we found significant correlations with the contralateral Crus II. We also compared longitudinal subdivisions of the hippocampus, revealing that anterior hippocampus demonstrated stronger connectivity with right Crus II, whereas posterior hippocampus was strongly connected to vermal parts of lobule V. Finally, we found that functional correlations between several hippocampal seeds (left, right, and anterior) and lobules HVI and HV decreased significantly with age. These results provide novel insights into hippocampal-cerebellar functional organisation and the influence of ageing on this system. Further studies are required to establish the role of this connection in learning and memory, as well as its potential vulnerability to neurodegeneration.

Cortical Reactivations Modulated by Local InhibitoryCircuits Mediate Memory Consolidation
Highly salient events activate neurons across various brain regions. During subsequent rest or sleep, the activity patterns of these neurons often correlate with those observed during the preceding experience. Growing evidence suggests that these reactivations play a crucial role in memory consolidation, the process by which experiences are solidified in cortical networks for long-term storage. Here, we demonstrate that reactivations in the lateral visual cortex are vital for the consolidation of visual association learning. By employing longitudinal two-photon Ca2+ imaging alongside paired LFP recordings in the hippocampus and cortex, we show that targeted manipulation of PV+ inhibitory neurons in the lateral visual cortex after daily training selectively attenuated cue-specific reactivations and learning, with no apparent effect on normal network function during training. In contrast, reactivations in the control group were biased towards salient cues, aligned with learning process and persisted for hours after training had ended. Overall, our results underscore a crucial role for cortical reactivations in memory consolidation.

An anterior hypothalamic circuit gates stress vulnerability
Prior adversity increases susceptibility to subsequent stressful events, but the causal underlying changes in brain circuitry are poorly understood. We harnessed unbiased whole-brain activity mapping to identify circuits that are functionally remodeled by prior adversity. This revealed that the anterior hypothalamic nucleus (AHN) displays heightened stress reactivity in previously stressed mice. This was accompanied by increased functional connectivity between the AHN and a threat-related limbic network. Using in vivo Miniscope imaging, we found that neuronal activity in the AHN encodes stressor valence. Moreover, stimulating AHN neurons enhanced, and inhibiting their activity mitigated, reactivity to stressful events. Lastly, silencing amygdala inputs to the AHN abolished the ability of prior adversity to increase stress sensitivity. These findings define a key role of the AHN in gating stress vulnerability by scaling valence signals from the amygdala.

The claustrum is critical for maintaining working memory information
Working memory (WM) enables the mammalian brain to temporarily store and manipulate information, supporting cognitive tasks and communication processes. Rather than depending on a single specialized area, WM is thought to operate through a distributed network spanning cortical and subcortical regions. A dedicated WM storage area would likely require broad reciprocal connections with various cortical regions to accommodate the diverse range of information WM retains. The claustrum (CLA), with its extensive bidirectional connections to the neocortex, presents a compelling candidate for such a role. Here, we examined the involvement of the CLA in WM processes by recording CLA neuronal activity in mice engaged in olfactory and tactospatial delayed non-match-to-sample WM tasks. We identified cue-selective and delay-specific neurons in the CLA that maintained activity for tens of seconds after the stimulus presentation ended. Additionally, population activity in the CLA allowed for decoding of cue identity post-stimulus, although this signal gradually declined over time, aligning with animal behavior. Remarkably, both chemo- and optogenetic inhibition of CLA neurons severely impaired WM performance across multiple types of stored information, highlighting the CLA's critical role during both cue encoding, delay periods, and target comparison phases. These findings challenge the view that no single brain area is essential for WM storage and support a role for the CLA as an essential WM storage hub.

On reconstruction of cortical functional maps using subject-specific geometric and connectome eigenmodes
Understanding the interplay between human brain structure and function is crucial to discern neural dynamics. This study explores the relation between brain structure and macroscale functional activity using subject-specific structural connectome eigenmodes, complementing prior work that focused on group-level models and geometry. Leveraging data from the Human Connectome Project, we assess accuracy in reconstructing various functional MRI-based cortical maps using individualised eigenmodes, specifically, across a range of connectome construction parameters. Our results show only minor differences in performance between surface geometric eigenmodes, a local neighborhood graph, a highly smoothed null model, and individual and group-level connectomes at modest smoothing and density levels. Furthermore, our results suggest that spatially smooth eigenmodes best explain functional data. The absence of improvement of individual connectomes and surface geometry over smoothed null models calls for further methodological innovation to better quantify and understand the degree to which brain structure constrains brain function.

Inclusivity in fNIRS Studies: Quantifying the Impact of Hair and Skin Characteristics on Signal Quality with Practical Recommendations for Improvement
Functional Near-Infrared Spectroscopy (fNIRS) holds transformative potential for research and clinical applications in neuroscience due to its non-invasive nature and adaptability to real-world settings. However, despite its promise, fNIRS signal quality is sensitive to individual differences in biophysical factors such as hair and skin characteristics, which can significantly impact the absorption and scattering of near-infrared light. If not properly addressed, these factors risk biasing fNIRS research by disproportionately affecting signal quality across diverse populations. Our results quantify the impact of various hair properties, skin pigmentation as well as head size, sex and age on signal quality, providing quantitative guidance for future hardware advances and methodological standards to help overcome these critical barriers to inclusivity in fNIRS studies. We provide actionable guidelines for fNIRS researchers, including a suggested metadata table and recommendations for cap and optode configurations, hair management techniques, and strategies to optimize data collection across varied participants. This research paves the way for the development of more inclusive fNIRS technologies, fostering broader applicability and improved interpretability of neuroimaging data in diverse populations.

The aberrant language network dynamics in autism ages 5-40 years
Background: Language impairments, which affect both structural aspects of language and pragmatic use, are frequently observed in autism spectrum disorder (ASD). These impairments are often associated with atypical brain development and unusual network interaction patterns. However, a neurological framework remains elusive to explain them. Methods: In this study, we utilized the dynamic "meta-networking" framework of language-a theoretical model that describes the domain-segregation dynamics during resting states-to investigate cortical language network abnormalities in ASD aged 5-40 years. Results: Our findings revealed distinct developmental trajectories for three domain-specific language subnetworks in ASD, characterized by unique patterns of hypo- and hyper-connectivity that vary with age. Notably, these language network abnormalities proved to be strong predictors of verbal Intelligence Quotient and communication deficits, though they did not predict social abilities or stereotypical behaviors. Limitations: Due to the limited availability of linguistic data, our study was unable to assess the language deficit profiles of individuals with ASD. Conclusions: Collectively, these findings refined our understanding of the network mechanisms for language and communication deficits in ASD.

Looking into working memory to verify potential targets during search
Finding what you are looking for is a ubiquitous task in everyday life that relies on a two-way comparison between what is currently viewed and internal search goals held in memory. Yet, despite a wealth of studies tracking visual verification behavior among the external contents of perception, complementary processes associated with visual verification among internal contents of memory remain elusive. Building on a recently established gaze marker of internal visual focusing in working memory, we tracked the internal inspection process associated with confirming or dismissing potential targets during search. We show how we look back into memory when faced with external stimuli that are perceived as potential targets and link such internal inspection to the time required for visual verification. A direct comparison between visual verification among the contents of working memory or perception further revealed how verification in both domains engages frontal theta activity in scalp EEG, but also how mnemonic verification is slower to deploy than perceptual verification. This establishes internal verification behavior as an integral component of visual search, and provides new ways to look into this underexplored component of human search behavior.

Shifts in Naturalistic Behaviors Induced by Early Social Isolation Stress are Associated with Adult Binge-like Eating in Female Rats
Binge eating (BE) is a highly pervasive maladaptive coping strategy in response to severe early life stress such as emotional and social neglect. BE is described as repeated episodes of uncontrolled eating and is tightly linked with comorbid mental health concerns. Despite social stressors occurring at a young age, the onset of BE typically does not occur until adulthood providing an interval for potential therapeutic intervention. Currently, our knowledge of longitudinal noninvasive digital biomarkers predictive of BE needs further development. Monitoring longitudinal impacts of adolescent social isolation stress on naturalistic behaviors in rats will enable the identification of noninvasive digital markers of disease progression to predict adult eating strategies. Recognizing adolescent naturalistic behaviors shaped by social stress informs our understanding of the underlying neurocircuits most effected. This study aimed to monitor and identify longitudinal behavioral shifts to enhance predictive capabilities in a rat model of social isolation stress-induced BE. We placed Paired (n=12) and Socially Isolated (SI, n=12) female rats in observational home cages weekly for seven weeks to evaluate the effect of SI on 10 naturalistic behaviors. All 10 naturalistic behaviors were simultaneously detected and tracked using Noldus Ethovision XT automated recognition software. Composite phenotypic z-scores were calculated by standardizing all 10 behaviors. When transitioning into adulthood, all rats underwent conventional emotionality testing and were exposed to a Western-like high fat diet (WD, 43% kcal from fat) to evaluate BE. Longitudinal assessments revealed SI-induced shifts in adolescent phenotypic z-scores and that sniffing, unsupported rearing, jumping, and twitching were the most susceptible to SI. SI increased emotionality compared to the Paired controls. Finally, we identified adolescent twitching as a digital biomarker of adult WD consumption. This study employed novel approaches to identify early life predictive biomarkers of adult eating strategies and laid a foundation for future investigations.

Mechanisms and purpose of lowered action potential firing threshold in fast-spiking interneurons in the human neocortex
The mammalian brain exhibits various interspecies differences. Microanatomical and molecular differences in homologous neurons between species are best characterized in the neocortical mantle, but the purpose of these differences remains poorly understood. We performed whole-cell microelectrode recordings and microanatomical and molecular analyses of human fast-spiking parvalbumin (pvalb)-expressing interneurons in neocortical tissue resected during brain surgery. Fast-spiking interneurons exhibited a lower action potential (AP) firing threshold in humans than in mice. Compared with mouse neurons, human neurons displayed an elongated axon initial segment (AIS), and the human AIS was deficient in low-voltage activated inhibitory Kv1 potassium channels. Contrarily, Kv1 ion channels were prominent in mouse neurons. Computational fast-spiking interneuron model simulations revealed that human-type AIS lowers the AP threshold and shortens the time lag for AP generation. Thus, human AIS supports fast in-fast out electrical circuit function in human pvalb neurons, which have electrically slow membrane potential kinetics in somata.

Catecholamines reduce choice history biases
Theoretical accounts postulate that the catecholaminergic neuromodulator noradrenaline shapes cognitive behavior by reducing the impact of prior expectations on learning, inference, and decision-making. A ubiquitous effect of dynamic priors on perceptual decisions under uncertainty is choice history bias: the tendency to systematically repeat, or alternate, previous choices, even when stimulus categories are presented in a random sequence. Here, we directly test for a causal impact of catecholamines on these priors. We pharmacologically elevated catecholamine levels through the application of the noradrenaline reuptake inhibitor atomoxetine. We quantified the resulting changes in observers' history biases in a visual perceptual decision task. Choice history biases in this task were highly idiosyncratic, tending toward choice repetition or alternation in different individuals. Atomoxetine decreased these biases (toward either repetition or alternation) compared to placebo. Behavioral modeling indicates that this bias reduction was due to a reduced bias in the accumulation of sensory evidence, rather than of the starting point of the accumulation process. Atomoxetine had no significant effect on other behavioral measures tested, including response time and choice accuracy. We conclude that catecholamines reduce the impact of a specific form of prior on perceptual decisions.

Rhythms and Background (RnB): The Spectroscopy of Sleep Recordings
Non-rapid eye movement (NREM) sleep is characterized by multiple coupled rhythms involved in memory consolidation, alongside an arrhythmic 1/f scale-free background also hypothesized to contribute to NREM sleep functions. Spectral parametrization methods have been recently introduced to describe the properties of rhythmic and arrhythmic processes in the spectral domain. However, these approaches fall short disentangling rhythms from arrhythmicity regarding the time series. This is crucial as arrhythmicity can impact the morphology of individual oscillations, therefore affecting their frequency, amplitude, waveform, and their cross-frequency coupling estimated transiently. We introduce 'Rhythms & Background' (RnB), an innovative wavelet-based methodology that compensates for arrhythmicity within the time domain. We validate RnB against spectral methods and demonstrate its enhanced capability to characterize the hallmark features of NREM sleep rhythms. Furthermore, RnB reveal the rhythmic time series, highlighting key NREM sleep rhythms with improved sensitivity to their phase-amplitude coupling.

Exploring the roles of memory replay in targeted memory reactivation and birdsong development: Insights from computational models of complementary learning systems
Replay facilitates memory consolidation in both biological and artificial systems. Using the complementary learning systems (CLS) framework, we study replay in both humans and birds through computational modelling. We investigate impacts of replay triggered by targeted memory reactivation during sleep and experiments examining how sleep affects the development of birdsong in young songbirds. We show that qualitatively realistic sleep effects can be captured by highly abstracted, idealised CLS models. Our modelling sheds theoretical insights on the mechanisms underlying both strengthening and weakening effects of targeted memory reactivation, and supports the empirical hypothesis that replay drives overnight performance deterioration and correlates positively with the final performance in birdsong development.

Association of cerebellar inflammation and neurodegeneration in a novel spinocerebellar ataxia type 13 mouse model
Background: Neuroinflammation is a recognized pathological characteristic of neurodegenerative diseases. Spinocerebellar ataxia 13 (SCA13) is a progressive neurodegenerative disease with no effective treatments. Our previous studies reported human mutations in KCNC3 gene are causative for SCA13. Human R423H allelic mutation induces early-onset neurodegeneration and aberrant intracellular retention of Epidermal Growth Factor Receptor (EGFR) in drosophila. However, the neurodegeneration and inflammatory response induced by the R424H allele are unknown in a mammalian model of disease. Method: In this study, a single Kcnc3 R424H mutation (Analogous to the human SCA13 R423H isoform) transgenic mice were created using CRISPR/Cas 9 technique. Motor function (gait, tremor, coordination and balance) and cerebellar volume (scanned and imaged with 7T MRI) of the R424H transgenic mice were evaluated at multiple timepoints. Neurodegeneration (Purkinje cells loss) as well as cerebellar (astroglia, microglia and macrophage activation) and peripheral (plasma cytokines levels) inflammatory responses were examined and analyzed. Result: The R424H transgenic mice showed marked neurological motor dysfunction with high-frequency tremor, aberrant gait, and short latency to fall in Rotarod testing at 3 and 6 months of age. Abnormal spontaneous firing was recorded in electrophysiology of Purkinje cells. Pathological changes in our R424H transgenic mice included progressive Purkinje cell degeneration and cerebellar atrophy. Over-active microglia, astrocytes, and macrophages were observed in the cerebella of transgenic mice. Pearson correlation analyses indicated that the number of Calbindin positive cells, a Purkinje cell marker, showed a strong inverse correlation with the positive cell number of EGFR, phosphorylated EGFR (pEGFR), and CD68. The expression of EGFR/pEGFR was positively correlated with CD68 and Glial Fibrillary Acidic Protein. Conclusion: Transgenic R424H mice provide a novel SCA13 model showing significant motor deficits, Purkinje cells loss, cerebellar inflammation, and atrophy. Our study suggests that the activation of inflammatory immune cells (astroglia, microglia and macrophages) and strong expression of EGFR/ pEGFR signal in these immune cells are associated with Purkinje cell loss in the cerebellum. This abnormal neuroinflammation may play a significant role in the aggressive procession of neurodegeneration.

Reductions of Grin2a in adolescent dopamine neurons confers aberrant salience and related psychosis phenotype
Psychosis is a hallmark of schizophrenia. It typically emerges in late adolescence and is associated with dopamine abnormalities and aberrant salience. Most genes associated with schizophrenia risk involve ubiquitous targets that may not explain delayed emergence of dopaminergic disruptions. This includes GRIN2A, the gene encoding the GluN2A subunit of the NMDA receptor. Both common and rare variants of GRIN2A are considered genetic risk factors for schizophrenia diagnosis. We find that Grin2a knockout in dopamine neurons during adolescence is sufficient to produce a behavioral phenotype that mirrors aspects of psychosis. These include disruptions in effort optimization, salience attribution, and ability to utilize feedback to guide behavior. We also find a selective effect of this manipulation on dopamine release during prediction error signaling. These data provide mechanistic insight into how variants of GRIN2A may lead to the latent presentation of aberrant salience and abnormalities in dopamine dynamics. This etiologically relevant model may aid future discovery of course altering treatments for schizophrenia.

Light tunes a novel long-term threat avoidance behavior
Animals must constantly scan their environment for imminent threats to their safety. However, they must also integrate their past experiences across long timescales to assess the potential recurrence of new threats. Though visual inputs are critical for the detection of environmental danger, whether and how visual information shapes an animal's assessment of whether a new threat is likely to reappear in a given context is unknown. Using a novel behavioral assessment of long-term threat avoidance behavior, we find that animals will avoid a familiar location where they previously experienced a single exposure to an innately threatening visual stimulus. This avoidance behavior is highly sensitive and lasts for multiple days. Intriguingly, we find that the melanopsin-expressing, intrinsically photosensitive retinal ganglion cells tune this behavior via a perihabenular-nucleus accumbens circuit distinct from the canonical visual threat detection circuits. These findings define a specific retinal cell type driving a new long-term threat avoidance behavior driven by prior visual experience.

The functional impact of LGI1 autoantibodies on human CA3 pyramidal neurons
Autoantibodies against leucine-rich glioma inactivated 1 protein (LGI1 mAb) lead to limbic encephalitis characterized by seizures and memory deficits. While animal models provide insights into mechanisms of LGI1 mAb action, species-specific confirmation is lacking. In this study, we investigated the effects of patient-derived LGI1 mAb on human CA3 neurons using cultured ex vivo slices. Analysis of intrinsic properties and morphology indicated functional integrity of these neurons under incubation conditions. Human CA3 neurons received spontaneous excitatory currents with large amplitudes and frequencies, suggestive of "giant" AMPA currents. In slices exposed to LGI1 mAb, human CA3 neurons displayed increased neuronal spike frequency, mirroring effects observed with the Kv1.1 channel blocker DTX-K. This increase likely resulted from decreased Kv1.1 channel activity at the axonal initial segment, as indicated by alterations in action potential properties. A detailed analysis revealed differences between LGI1 mAb and DTX-K effects on action potential properties, suggesting distinct mechanisms of action and emphasizing the need for further exploration of downstream pathways. Our findings underscore the importance of species specific confirmatory studies of disease mechanisms and highlight the potential of human hippocampal slice cultures as a translational model for investigation of disease mechanisms beyond epilepsy, including the effects of pharmacological compounds and autoantibodies.

Reduced Folate Carrier 1 (RFC1/Slc19a1) Suppression Exacerbates Blood-Brain Barrier Breakdown in Experimental Ischemic Stroke in Adult Mice
The Reduced Folate Carrier 1 (RFC1), also called solute carrier family 19 member 1 (SLC19A1/SLC19a1), is recognized for transporting folates across the blood-brain barrier (BBB). RFC1 has recently been defined as a hypoxia-immune related gene whose expression levels were induced by acute retinal ischemia, suggesting that RFC1 may have a role in the response of the brain to ischemic injury. Despite a recent human meta-analysis suggesting an association between certain RFC1 polymorphisms and the risk of silent brain infarctions, preclinical evidence concerning the potential role of RFC1 in acute ischemic stroke has yet to be presented. To investigate this, we first characterized RFC1 protein expression in mouse microvessels and pericytes which play significant roles in stroke pathophysiology. Then, we examined the temporal (1-h, 24-h, and 48-h) and spatial (infarct, periinfarct, contralateral) expression of RFC1 protein in the intraluminal transient middle cerebral artery occlusion mouse model. Finally, we knocked down RFC1 protein with RFC1-siRNA in the potential periinfarct region before induction of ischemia and investigated BBB integrity and infarct size in vivo via 7T-MRI. Moreover, we utilized a pharmacological modulation -methotrexate, a non-covalent inhibitor of RFC1- to further investigate the role of RFC1 in maintaining BBB integrity. Our study revealed that, i) RFC1 protein levels were dynamic throughout the acute phases of ischemic stroke, ii) RFC1 suppression aggravated the BBB leakage during ischemia. These results emphases the role of RFC1 in the pathophysiology of ischemic stroke and supports the evidence from human studies.

Microsaccades strongly modulate but do not cause the N2pc EEG marker of spatial attention
The N2pc is a popular human-neuroscience marker of covert and internal spatial attention that occurs 200-300 ms after being prompted to shift attention - a time window also characterised by the spatial biasing of microsaccades. Here we show how co-occurring microsaccades profoundly modulate N2pc amplitude during the top-down deployment of spatial attention in both perception and working memory. At the same time, we show that a significant - even if severely weakened - N2pc can still be established in the absence of co-occurring microsaccades. Thus, while microsaccade presence and direction strongly modulate N2pc amplitude, microsaccades are not strictly a prerequisite for the N2pc to be observed.

Genetic and functional adaptations and alcohol-biased signaling in the mediodorsal thalamus of alcohol dependent mice
Alcohol Use Disorder (AUD) is a significant health concern characterized by an individual's inability to control alcohol intake. With alcohol misuse increasing and abstinence rates declining, leading to severe social and health consequences, it is crucial to uncover effective treatment strategies for AUD by focusing on understanding neuroadaptations and cellular mechanisms. The mediodorsal thalamus (MD) is a brain region essential for cognitive functioning and reward-guided choices. However, the effects of alcohol (ethanol) dependence on MD neuroadaptations and how dependence alters MD activity during choice behaviors for alcohol and a natural reward (sucrose) are not well understood. Adult C57BL/6J mice treated with chronic intermittent ethanol (CIE) exposure were used to assess genetic and functional adaptations in the MD. Fiber photometry-based recordings of GCaMP6f expressed in the MD of C57BL/6J mice were acquired to investigate in vivo neural adaptations during choice drinking sessions for alcohol (15%) and either water or sucrose (3%). There were time-dependent changes in cFos and transcript expression during acute withdrawal and early abstinence. Differentially expressed genes were identified in control mice across different circadian time points and when comparing control and alcohol dependent mice. Gene Ontology enrichment analysis of the alcohol-sensitive genes revealed disruption of genes that control glial function, axonal myelination, and protein binding. CIE exposure also increased evoked firing in MD cells at 72 hours of withdrawal. In alcohol-dependent male and female mice that show increased alcohol drinking and preference for alcohol over water, we observed an increase in alcohol intake and preference for alcohol when mice were given a choice between alcohol and sucrose. Fiber photometry recordings demonstrated that MD activity is elevated during and after licking bouts for alcohol, water, and sucrose, and the signal for alcohol is significantly higher than that for water or sucrose during drinking. The elevated signal during alcohol bouts persisted in alcohol dependent mice. These findings demonstrate that CIE causes genetic and functional neuroadaptations in the MD and that alcohol dependence enhances alcohol-biased behaviors, with the MD uniquely responsive to alcohol, even in dependent mice.

Mu opioid receptor expression by nucleus accumbens inhibitory interneurons promotes affiliative social behavior
Mu opioid receptors in the nucleus accumbens regulate motivated behavior, including pursuit of natural rewards like social interaction as well as exogenous opioids. We used a suite of genetic and viral strategies to conditionally delete mu opioid receptor expression from all major neuron types in the nucleus accumbens. We pinpoint inhibitory interneurons as an essential site of mu opioid receptor expression for typical social behavior, independent from exogenous opioid sensitivity.

Activity-dependent extracellular proteolytic cascade remodels ECM to promote structural plasticity
The brain's perineuronal extracellular matrix (ECM) is a crucial factor in maintaining the stability of mature brain circuitry. However, how is activity-induced synaptic plasticity achieved in the adult brain with a dense ECM? We hypothesized that neuronal activity induces cleavage of ECM components, creating space for synaptic rearrangements. To test this hypothesis, we investigated neuronal activity-dependent proteolytic cleavage of brevican, a prototypical perineuronal ECM proteoglycan, and its importance of this process for functional and structural synaptic plasticity in the rat hippocampus ex vivo. Our findings revealed that chemical long-term potentiation (cLTP) triggers a rapid brevican cleavage through the activation of an extracellular proteolytic cascade involving proprotein convertases and ADAMTS-4 and ADAMTS-5. This process is dependent on NMDA receptors and requires astrocytes. Interestingly, the extracellular full-length brevican increases upon cLTP, indicating a simultaneous secretion of ECM components. Interfering with cLTP-induced brevican cleavage did not impact the early LTP but prevented formation of new dendritic protrusions. Collectively, these results reveal a mechanism of activity-dependent ECM remodeling and suggest that ECM degradation is essential for structural synaptic plasticity.