bioRxiv Subject Collection: Neuroscience's Journal

Endothelial tight junctions and cell-matrix adhesions reciprocally control blood-brain barrier integrity
Brain endothelial cells (ECs) rely on mechanical cues to provide a physical barrier that protects the brain. Yet how ECs integrate forces to establish and maintain the blood-brain barrier (BBB) remains poorly understood. Here, we show that the two main endothelial force-bearing systems, tight junctions and cell-matrix adhesions, reciprocally control BBB integrity. Using a combination of super-resolution imaging and biophysical techniques, we reveal increasing mechanical loads on cell-cell junctions vs. cell-matrix adhesions in human stem cell-derived ECs during BBB maturation. This force redistribution is enabled by cytoskeletal remodeling, a compacted pattern of the tight junction protein claudin 5, and the emergence of specialised perinuclear cell-matrix adhesions. Mechanistically, we find an inverse relationship between claudin-5 levels and the expression of key cell-matrix adhesion proteins zyxin and vinculin in vitro and in mice. Finally, we demonstrate that this mechanobiological signature associated with BBB maturation is reversed upon BBB dysfunction after seizures in mice and in human patients with temporal lobe epilepsy. Collectively, our findings establish a novel interplay between mechanoresponsive elements in brain ECs, with implications for BBB stabilisation therapy in epilepsy.

Dopaminergic neurons are vulnerable to dysregulation of YEATS2-dependent calcium homeostasis
YEATS2 is a ubiquitously expressed chromatin-associated factor that we recently identified as a novel regulator of dopaminergic (DAergic) synaptic integrity, though its mechanism of action remained unclear. Using Drosophila, we show that neuronal depletion of YEATS2 reshapes the brain transcriptome, marked by downregulation of metabolic genes and upregulation of G protein-coupled receptors (GPCRs). These changes coincide with elevated intracellular calcium, neurobehavioral deficits, and selective DA neuron loss. Importantly, genetic or pharmacological inhibition of the store-operated calcium entry channel Orai restored calcium homeostasis and rescued DA neuron survival. Our findings define a YEATS2-dependent epigenetic-calcium axis that governs DA neuron vulnerability.

Modeling interaction between focal cerebral ischemia and Alzheimer`s Disease Pathology in an APP/PS1 Mouse Model
Ischemic stroke is one of the leading causes of death and disability in the United States and is a known risk factor for Alzheimer`s Disease (AD) development. One of the characteristics of AD is the accumulation of {beta}-amyloid peptide due to the proteolysis of Amyloid Precursor Protein (APP) by the protein Presenilin 1 (PS1). The study of interaction between ischemia and AD has been limited due to lack of experimental models. The current study describes a novel model utilizing a brief transient ischemia (15 min MCAO) in an AD mouse model to assess mechanistic interaction. Here we investigate the effects of increased {beta}-amyloid peptide on motor coordination, behavioral and cellular memory, when subjected to brief focal ischemia. APP/PS1 or Wt male mice are initially subjected to either a 15-minute MCAO or Sham surgery. Injury volume using MRI is assessed at 3-days using T2 imaging and demonstrates that injury magnitude was not different between Wild-type and APP/PS1 mice. We observed that 15 min MCAO did not cause significant motor deficits in either WT or APP/PS1 mice, as measured by open field and tapered balance beam. Short-term memory was assessed 7 days after recovery from brief MCAO using the contextual fear conditioning task. APP/PS1 mice exhibited intact memory at 3 months of age and Wt mice also having intact memory 7 days after 15 min MCAO. In contrast, APP/PS1 + 15 min MCAO mice exhibited a significant reduction in freezing behavior suggesting impairment in short term memory. Consistent with our contextual fear conditioning, we observed impaired hippocampal long-term potentiation (LTP) in APP/PS1 + 15 min MCAO compared to their sham counterparts. Remarkably, we observed an additive effect of ischemia and AD, with cellular and behavior memory deficits observed in APP/PS1 mice exposed to brief ischemia that does not cause symptoms in WT mice. This study represents an important new model to be study the mechanistic link between ischemia and accelerated AD progression.

Distinct brain regions map olfactory and visual spaces
The hippocampus contains a multisensory cognitive map that incorporates spatial cues from across the senses, such as vision and olfaction. However, how primary sensory information transforms along pathways to the hippocampus into this single, combined map is largely unknown. Specifically, does the hippocampus generate or inherit the multisensory map of space? Here, we used multisensory virtual reality and large-scale functional imaging to determine if and how the main input regions to hippocampus, the lateral and medial entorhinal cortices (LEC and MEC, respectively), map olfactory and visual sensory spaces in navigating mice. We discovered that, in contrast to multisensory mapping in the hippocampus, LEC preferentially maps olfactory space while MEC preferentially maps visual space, regardless of the behavioral relevance of the spaces. This establishes the existence of largely independent brain maps for different sensory spaces, suggesting that the hippocampus builds the cognitive map by combining modality-specific maps from pre-synaptic cortical regions.

Plasticity in thoracic paravertebral sympathetic postganglionic neurons after high spinal cord transection
Various pre-sympathetic descending brain circuits recruit spinal cord preganglionic neurons to encode central sympathetic drive via their synaptic actions onto sympathetic postganglionic neurons (SPNs) - the final sympathetic output neurons. Thoracic paravertebral ganglia SPNs (tSPNs) provide distributed control over body tissue systems via functional subpopulations. High thoracic spinal cord injuries (SCIs) compromise descending excitatory drive to SPNs, causing dysautonomias including hypotension. In adult mice, we tested whether the SCI-induced chronic reduction in tSPN activity leads to homeostatic increases in their excitability. tSPN excitability spanned a >10 fold range in both sham and SCI populations, governed by a strong linear (ohmic) relationship between cell resistance and threshold depolarizing current (rheobase), with a clear trend towards increased excitability after SCI. Dendritic length was reduced, as was measured cell capacitance in Neuropeptide Y expressing (NPY+) tSPNs (putative vasoconstrictors), which represent >40% of tSPNs. NPY+ tSPNs also had changes in active membrane properties including an increased repetitive firing output gain ({uparrow}f-I slope), which modelling attributed to reduced delayed rectifier currents (IK). After SCI, spontaneous quantal excitatory synaptic frequency increased overall (226%) and in the NPY+ tSPN subpopulation (300%); their temporal summation recruited spiking in 10.5% of sham and 22.2% of SCI recordings. Computational modeling showed that spontaneous synaptic activity was particularly effective at recruiting spiking after SCI. Overall, tSPNs, including in vasoconstrictors, appear to undergo CNS-independent compensatory increases in excitability after SCI. The alterations further contribute to observed central and peripheral changes that limit hypoactivity and hypotension but exaggerate reflex responses.

Mechanisms of Neural Representation and Segregation of Multiple Spatially Separated Visual Stimuli
Segregating objects from one another and the background is essential for scene understanding, object recognition, and visually guided action. In natural scenes, it is common to encounter spatially separated stimuli, such as distinct figure-ground regions, adjacent objects, and partial occlusions. Neurons in mid- and high-level visual cortex have large receptive fields (RFs) that often encompass multiple, spatially separated stimuli. It is unclear how neurons represent and segregate these stimuli within their RFs. We investigated this question by recording the neuronal responses in the middle temporal (MT) cortex from two male macaque monkeys to multiple moving stimuli. We placed a motion border between two spatially separated random-dot patches that moved in two different directions within the RFs. We varied the vector average direction of the stimuli to characterize the full direction tuning curves. Across motion directions, responses to multiple stimuli were systematically biased toward the stimulus located at the more-preferred RF subregion of the neuron. The sign and magnitude of this spatial-location bias were correlated with the spatial preference of the neuron measured with single patches presented in isolation. We demonstrated that neuronal responses to multiple stimuli can be captured by an extended divisive normalization model, as a sum of the responses elicited by individual stimuli, weighted by the spatial preference of the neuron. We also proposed a circuit implementation for the extended normalization model. Our results indicate that MT leverages spatial selectivity within the RFs to represent spatially separated moving stimuli. The spatial-location bias in neuronal responses enables individual components of multiple stimuli to be represented by a population of neurons with heterogeneous spatial preferences, providing a neural substrate for segregating multiple visual stimuli.

Electrode position, size, and orientation determine efficacy of cervical epidural stimulation to recruit forelimb muscles in rats
Objective: Cervical epidural spinal cord stimulation (SCS) can facilitate upper-limb motor recovery, but electrode configurations that optimally recruit motor circuits remain unclear. This study systematically evaluated how electrode position, size, orientation, and waveform influence the efficacy of forelimb motor activation in rats, with the goal of identifying configurations that minimize stimulation thresholds of evoked responses across multiple muscles. Approach: Custom microfabricated arrays of electrodes were implanted over the C6 dorsal root entry zone (DREZ) in eight adult female Sprague Dawley rats. A circular array was used to vary current orientation in 45 degree increments, while a linear array was used to optimize mediolateral electrode position. The linear array included both small (0.25 mm) and large (0.5 mm) contacts to assess size effects at mediolateral positions. Stimulation consisted of biphasic and pseudomonophasic waveforms with bipolar or distant return, and a high-definition montage to probe spatial focality around the DREZ. Motor-evoked potentials (MEPs) recorded via implanted EMG electrodes were analyzed in six forelimb muscles. Thresholds, estimated from recruitment curves using a hierarchical Bayesian model, were compared within-rat using pairwise t-tests with correction for multiple comparisons. Results: Stimulation over the DREZ yielded the lowest thresholds and efficacy decreased progressively with medial or lateral displacement relative to DREZ. In the circular array, rostro-caudal current orientation was most effective, reducing thresholds by up to 58% relative to latero-medial orientation (p = 0.0007). In the linear array, large contacts were significantly more effective than small contacts at the lateral position, reducing thresholds by 45% (p = 0.034). Cathodal stimulation was more effective than anodal, and high-definition montages reduced efficacy compared to distant returns. Across all tested parameters, position and orientation had the greatest influence on efficacy, with optimal conditions combining DREZ targeting and rostro-caudal oriented current flow. Significance: Maximum efficacy was achieved for cervical SCS with electrodes positioned over the DREZ, rostro-caudal current flow, larger contacts, and cathodal stimulation. These design principles that more effectively engage spinal circuitry could reduce the current required and thereby improve SCS systems for upper-limb motor restoration.

Postnatal development of pyramidal neurons excitability and synaptic inputs in mouse gustatory cortical circuits
Cortical neurons in sensory areas undergo a protracted process of postnatal maturation that includes changes in membrane properties, synaptic drive and connectivity. The completion of this process is associated with the closure of sensitive windows for experience-dependent plasticity. Weaning is a critical time in the development of taste circuits as animals transition from depending on the mother for nutrition to eating independently. While there is some evidence for developmental changes in taste bud innervation and in membrane properties of neurons in brainstem circuits for taste, very little is known about postnatal changes in the gustatory cortex (GC), the primary cortical region for taste and taste-guided behaviors. Here, we focused on pyramidal neurons in the deep layers of GC and compared their membrane properties in pre- and postweaning age groups. We report dynamic changes in intrinsic excitability and a progressive shift of the excitation/inhibition (E/I) balance toward inhibition as pyramidal neurons reach their young adult properties. The increase in inhibitory drive accompanied a protracted process of postnatal maturation of inhibitory circuits mediated by parvalbumin expressing neurons (PV neurons) that showed a progressive increase in their association with perineuronal nets (PNNs) and refinement of their connectivity onto pyramidal neurons. Together, our results indicate that GC neurons undergo protracted postnatal maturation that may influence taste response properties at the transition to independent feeding.

Probability weighting arises from boundary repulsions of cognitive noise
In both risky choice and perception, people overweight small and underweight large probabilities. While prospect theory models this with a probability weighting function, and Bayesian noisy coding models attribute it to specific encoding functions or priors, we propose a more general account: Probability distortions arise from cognitive noise being repelled by the natural boundaries of probability (0,1). This boundary repulsion occurs in any encoding-decoding system that efficiently encodes, or Bayesian-decodes, bounded quantities, independent of specific priors or encoding functions. Our theory predicts: new, experimentally-induced boundaries should cause additional distortions; increasing cognitive noise should amplify distortions; and boundaries should reduce behavioral variability near them. We confirmed all predictions in three pre-registered experiments spanning risky choice and probability perception. Our findings further suggest that these changes originate largely during decoding. Our work provides a unified explanation for distorted and variable probability judgments, reframing them as consequences of bounded, noisy cognitive inference.

A median eye origin of the vertebrate retina explains its unique circuitry
The vertebrate retina is a uniquely complex and evolutionarily conserved structure among bilaterians, combining ciliary (rods and cones) and rhabdomeric (ganglion, amacrine, and horizontal) photoreceptor lineages within a multilayered circuit. This arrangement contrasts with the ancestral bilaterian cephalic pattern, where rhabdomeric photoreceptors dominate lateral eyes and ciliary photoreceptors are limited to unpigmented, non-visual median positions. We propose that the vertebrate retina evolved through the lateralization of a complex median photoreceptive organ already containing both photoreceptor types. This shift likely followed the loss of lateral rhabdomeric eyes in a burrowing, suspension -feeding deuterostome ancestor and the retention of a median eye. In the early chordates leading to vertebrates, this structure diversified into the pineal/parapineal complex and lateral retinas. Central to this transformation was the emergence of a bipolar cellular identity, linking ciliary and rhabdomeric circuits - an unusual feature in animal nervous systems. We suggest bipolar cells have dual evolutionary origins: Off bipolar cells from a ciliary 'effector' lineage and rod -On bipolar cells from a chimeric sensory cell. This model explains key similarities between retina and pineal and supports a scenario in which vertebrate vision emerged by integrating and repurposing preexisting circuits. It reframes the retina not as a de novo innovation, but as a modified and lateralized, solution to sensory challenges faced by early chordates.

Dual hypocretin receptor antagonism enhances sleep and nursing behavior in lactating rats.
Hypocretins (also known as orexins) are neuropeptides that regulate the sleep-wake cycle and modulate various behaviors, including maternal behavior. They act through two receptor subtypes: hypocretin receptor 1 (HcrtR1) and hypocretin receptor 2 (HcrtR2). Although Dual Orexin Receptor Antagonists (DORAs) are clinically used as hypnotics, most preclinical studies with these drugs have been conducted in males, with limited research in females, leaving the postpartum period largely unexplored. Here, we examined the impact of the DORA Suvorexant on sleep and maternal behavior in lactating rats. Lactating and virgin female rats were implanted with electrodes for polysomnographic recording. Using a counterbalanced design, Suvorexant was orally administered at doses of 0, 10 (SUV10), and 30 mg/kg (SUV30) to virgin rats in diestrus and to lactating rats between postpartum days 4 and 8. Sleep recordings and maternal behaviors were assessed during the light phase for six hours following the administration of the drug. Suvorexant reduced wakefulness and increased slow wave sleep, intermediate state, and REM sleep in both groups, with a stronger effect in virgin females. In lactating rats, Suvorexant increased nursing time and milk ejections, while reducing active maternal behavior such as pup-licking. These findings demonstrate that dual hypocretin receptor antagonism produces hypnotic effects and selectively modulates maternal behavior, promoting nursing while reducing active maternal behavior.

Next-generation hybridization chain reaction tools with enhanced sensitivities to detect challenging targets
Compared to traditional enzyme-based in situ amplification methods, Hybridization Chain Reaction v3.0 (HCR v3.0) offers high specificity for spatial RNA visualization but lacks the sensitivity needed for short or low-abundance targets, especially in thick tissue with high autofluorescence. We describe next-generation HCR detection methods that combine the specificity of HCR v3.0 with enzyme-based signal amplification through catalysis (HCR-Cat) or immunostaining (HCR-Immuno, HCR-Multi). These methods enhance sensitivity for robust spatial detection of both short and low-abundance targets, work well in challenging tissue environments, and enable broad utility across basic research and translational applications. These methods allow spatial detection of challenging targets that are poorly-accessible using HCR v3.0, as well as quantitative analysis of single transcripts even when targeting short RNAs with a limited number of probes.

Subanesthetic ketamine administration decreases deviance detection responses at the cellular, populational and mesoscale connectivity levels
In the neocortex, neuronal processing of sensory events is significantly influenced by context. For instance, responses in sensory cortices are suppressed to repetitive stimuli, a phenomenon termed stimulus-specific adaptation. However, in a context in which that same stimulus is novel, or deviates from expectations, neuronal responses are enhanced. Mismatch negativity (MMN), the electroencephalography waveform reflecting rule violations, is a well-established biomarker for auditory deviant detection. MMN has been shown to depend on intact NMDA receptor signaling across species; nevertheless, the underlying mechanisms are still not completely elucidated at the neural and mesoscale levels. Using multi-electrode array recordings in awake mice, we identified a specific biphasic spiking response in a subpopulation of A1 neurons elicited by deviant, but not standard, sounds, whereby the second peak is abolished by acute subanesthetic injection of ketamine, a partial non-competitive NMDA receptor antagonist. We further showed that the posterior parietal cortex, a critical hub for multisensory integration and sensorimotor coordination, responds to unexpected and deviant, but not repetitive, sounds, and this response is dependent upon intact NMDA receptor-mediated signaling. Finally, to explore the effects of ketamine on inter-cortical communication during deviance detection, we performed Granger Causality and Weighted Phase Lag Index (WPLI) analyses during the presentation of deviant and standard sounds. This analysis showed a unidirectional functional connectivity from A1 to PPC during deviant detection, which is impaired by subanesthetic ketamine administration. By investigating how ketamine modulates neural and inter-regional communication, our findings provide novel insights into the NMDA receptor-dependent mechanisms underlying the processing of novelty and regularity in auditory stimuli.

Confidence judgements from fused multisensory percepts
Distinguishing between reliable and unreliable internal sensory representations is crucial for a successful interaction with the environment. Precise estimates of the uncertainty of sensory representations are critical to optimally integrate multiple sensory modalities and produce a coherent interpretation of the world. However, once a multisensory percept is produced, it is not yet known whether humans still have access to the uncertainty of each sensory modality. Here, we asked human participants to perform a series of temporal bisection tasks, in either unimodal visual or auditory conditions, or in bimodal audiovisual conditions where vision and audition could be congruent or not. The validity of their temporal bisection was assessed by asking participants to choose which of two consecutive decisions they felt more confident of being correct, focussing only on the visual modality. We found that once multisensory information is integrated, participants could no longer access the unisensory information to evaluate the validity of their decisions. Comparing three generative models of confidence, we show that confidence judgments are fooled by the fused bimodal percept. These results highlight that some critical information is lost between perceptual and metaperceptual stages of processing in the human brain.

Scaling Personalized TMS: A Scalp-Based MRI-guided Alternative to Neuronavigation
Background: Personalized transcranial magnetic stimulation (TMS) has shown promise in treating psychiatric and neurological disorders, but its accessibility is limited by reliance on costly and complex neuronavigation systems, particularly in resource-constrained clinical settings. Objective: To develop and validate a scalp-based alternative to neuronavigation for personalized TMS targeting. Methods: We developed a Continuous Proportional Coordinate (CPC) system-based approach for personalized TMS targeting and validated its performance through three operators across ten participants, using individualized DLPFC-SGC targets as an example. The validation framework included targeting consistency assessment, reproducibility evaluation, and cross-cortical generalizability analysis. Results: The CPC-based approach demonstrated comparable performance to neuronavigation, achieving 99.4% of its electric field strength (74.80 vs. 75.14 V/m; r=0.962) and 93.9% of DLPFC-SGC functional connectivity (-0.216 vs. -0.230; r=0.949), with high inter-operator reliability (ICC[≥]0.903). Reproducibility analysis showed strong correlation between sessions (r=0.948-0.957) with high reliability. Further simulations across 1,125 uniformly distributed cortical targets supported generalizability of this approach, with stable electric field preservation (99.07{+/-}1.54%) across different brain regions. Conclusions: The CPC-based approach offers a practical alternative to neuronavigation, maintaining targeting accuracy and providing a more accessible option for personalized TMS implementation.

Temporal dynamics of CNS cholesterol esters correlate with demyelination and remyelination
Elevated cholesterol ester levels have been observed in the CNS of patients with neurological diseases, yet the source of cholesterol ester accumulation and whether it is directly linked to demyelination remains undefined. This study investigates the temporal dynamics of cholesterol esters using the Plp1-iCKO-Myrf mouse model, which features distinct phases of demyelination and remyelination. Our findings reveal that cholesterol ester levels increased with demyelination in both the brain and the spinal cord. In the brain, cholesterol esters declined to normal levels during remyelination, whereas cholesterol esters remained elevated in the spinal cord, which had limited remyelination. Expression of both acetyl-CoA-acyltransferase 1 (ACAT1) and lecithin-cholesterol acyltransferase (LCAT) were elevated during demyelination, suggesting the potential involvement of both proteins in the formation of cholesterol esters. Co-localization studies revealed that ACAT1 is predominantly expressed by microglia and LCAT is predominantly expressed by astrocytes during demyelination highlighting the active roles of glia cells in cholesterol ester metabolism. In addition, we showed that administering the remyelinating drug, Sob-AM2, effectively reduced the level of cholesterol ester accumulation in the brain during demyelination underscoring the potential that manipulating cholesterol ester regulatory pathways may offer for restoring cholesterol homeostasis and promoting remyelination in demyelinating diseases.

Nicotine in E-Cigarette Aerosol Reduces GABA Neuron Migration via the α7 Nicotinic Acetylcholine Receptor
Prenatal nicotine exposure is linked to adverse neurodevelopmental outcomes, yet e-cigarette use during pregnancy continues to rise due to aggressive marketing efforts and misconceptions of safety. We investigated the effect of prenatal e-cigarette aerosol exposure on the migration of GABA neurons, a developmental process critical for the establishment of cerebral cortical circuitry. Pregnant mice were exposed to nicotine-containing aerosol (e cigarette), nicotine-free aerosol (e-liquid) or room air (control) daily beginning 2 weeks before conception and continuing until gestational day 14. E-cigarette, but not e-liquid, aerosol significantly reduced GABA neuron density in the dorsal cerebral wall at rostral forebrain level and within the marginal zone, reflecting region-specific vulnerabilities. In vitro explant cultures revealed that nicotine dose-dependently reduced neuronal migration, and this effect was mimicked by a selective 7 nicotinic acetylcholine receptor (nAChR) agonist. Blocking the 7 nAChR using a selective antagonist attenuated the effects of nicotine on neuronal migration. These findings reveal a previously unrecognized vulnerability of GABA neuron migration to e-cigarette aerosol and identify 7 nAChR activation as a mechanism for nicotine-induced impairment of GABA neuron migration. Moreover, the findings highlight the need for translational efforts to update clinical guidance and public policy regarding e-cigarette use during pregnancy.

Local infrared stimulation modulates spontaneous cortical slow wave dynamics in anesthetized rats
Cortical slow waves are hallmark oscillations of deep sleep and certain anesthetic conditions, yet the neurobiological mechanisms controlling their dynamics remain incompletely understood. Here, we investigated the effects of local near-infrared (NIR) stimulation on slow-wave activity in ketamine/xylazine-anesthetized rats. Using a silicon-based multimodal optrode, we simultaneously delivered NIR light and recorded local field potentials (LFPs) and multi-unit activity (MUA) across cortical layers in the primary somatosensory (S1Tr) and parietal association (PtA) cortices. NIR stimulation induced local tissue heating, resulting in reproducible and reversible changes in the properties of slow waves. Specifically, up-state durations were shortened, down-states prolonged, and MUA amplitudes during up-states increased, with steeper slopes at state transitions, indicative of enhanced neuronal synchronization. LFP amplitude and spectral changes varied across cortical regions: PtA exhibited increased slow wave (0.5 - 2 Hz) and high delta (2 - 4 Hz) band activity, while S1Tr showed a trend toward reduction. Our findings demonstrate that local infrared stimulation can reliably modulate cortical slow-wave dynamics, likely through temperature-mediated changes in neuronal excitability. This approach provides a minimally invasive method for precise, local manipulation of cortical network activity and offers new insights into the biophysical regulation of slow oscillations.

Improving the utility and accuracy of wearable light loggers and optical radiation dosimeters through auxiliary data, quality assurance, and quality control
In chronobiology and circadian health-related fields, wearable light loggers and optical radiation dosimeters are increasingly used to capture personal light exposure, but their data often lack essential contextual information (e.g. non-wear periods, sleep, activity or environmental conditions) and can be compromised by wearer compliance and technical issues. To address these challenges, we conducted a mixed-methods study (21 expert interviews; n=16 survey respondents) to iteratively develop auxiliary data and quality-control strategies that enhance the utility and accuracy of wearable light data. We derived an auxiliary data framework spanning six domains - wear/non-wear logging, sleep monitoring, light-source context, participant behaviour, user experience, and environmental light levels - to systematically augment wearable recordings. Survey respondents showed overwhelming consensus on the value of auxiliary data (mean importance 4.0 out of 5). In particular, tracking sleep and wear time was rated as the most critical augmentation. To facilitate implementation, we provide concrete tools - notably the open-source R package LightLogR - for streamlined integration of wearable and auxiliary data and for facilitation of quality assurance. Our findings indicate that combining contextual logs with rigorous quality assurance and quality control markedly improves the reliability of field-collected light exposure data. These recommendations and tools will help researchers in chronobiology, wearable technologies, and health to maximise data quality and interpretability in real-world light-exposure studies.

Intravital Two-Photon Imaging of Touch Sensory Axon Morphology in Mouse Skin
Low-threshold mechanoreceptors (LTMRs) are somatosensory neurons that detect innocuous light touch stimuli such as vibration, hair deflection, and pressure. They form subtype-specific terminals in the periphery and project axons centrally to the spinal cord to transmit tactile information. Current understanding about LTMR development and organization comes from fixed-tissue studies that cannot reveal the dynamic and temporal processes of neuronal wiring and remodeling. Here, we demonstrate a two-photon imaging method for visualizing LTMR axon morphology in the mouse right forepaw during development and in young adults. Two-photon microscopy can achieve high-resolution imaging within intact skin, allowing repeated imaging of the same axon terminals over postnatal timepoints. These approaches provide an in vivo system for studying the cellular mechanisms that regulate LTMR patterning and plasticity. Its application to longitudinal analyses will enable the observation of the assembly of touch circuits and their repair following injury. This technique may provide essential information about somatosensory axon structure and function in the skin.

Comparative single-cell multiomic analysis reveals evolutionarily conserved and species-specific cellular mechanisms mediating natural retinal aging.
Biological age is a major risk factor in the development of common degenerative retinal diseases such as age-related macular degeneration and glaucoma. To systematically characterize molecular mechanisms underlying retinal aging, we performed integrated single-cell RNA- and ATAC-Seq analyses of the retina and retinal pigment epithelium (RPE) across the natural lifespan in zebrafish, mice, and humans. By profiling gene expression and chromatin accessibility, we identified extensive cell type- and species-specific aging-dependent changes, with a much smaller number of broadly expressed and conserved genes that include regulators of inflammation and autophagy. We constructed predictive aging clocks for retinal cell types and observed dynamic, reversible shifts in cellular age following acute injury. Spatial transcriptomic analysis revealed region-specific aging signatures and proximity effects, with Muller glia exhibiting pro-rejuvenating influences on neighboring neurons. Targeted Muller glia-specific induction of Yamanaka factors reduced molecular age in rod photoreceptors and bipolar cells without altering glial age. Our findings define conserved and divergent regulatory and signaling pathways mediating retinal aging, highlighting Muller glia as potential therapeutic targets for combating age-associated retinal dystrophies.

No effect of continuous transcutaneous auricular vagus nerve stimulation on the P3 and the P600 in an oddball and sentence comprehension task
The ERP components P3 and P600 have been proposed to reflect phasic activity of the locus coeruleus norepinephrine (LC/NE) system in response to deviant and task-relevant stimuli across cognitive domains. Yet, causal evidence for this link remains limited. Here, we used continuous transcutaneous auricular vagus nerve stimulation (taVNS), a non-invasive method proposed to modulate LC/NE activity, to test whether these components are indeed sensitive to noradrenergic manipulation. Forty participants completed both an active visual oddball task and a sentence processing task including both syntactic and semantic violations, while receiving continuous taVNS at the cymba conchae in one session and sham stimulation at the earlobe in another session. We observed robust P3 and P600 effects. Crucially though, taVNS had no effect on P3 or P600 amplitude. The physiological NE markers salivary alpha amylase level and baseline pupil size were also unaffected by the stimulation, suggesting that the taVNS protocol and/or task may not have been sufficient to successfully engage the norepinephrine system. Beyond the stimulation, however, exploratory analyses revealed correlations between the syntactic P600 and both the P3 and salivary alpha amylase levels, supporting the idea that the P600 might be related to both the P3 and NE. Overall, our findings do not allow for theoretical implications concerning a potential causal link between the two components and NE but highlight the need for more standardized taVNS protocols.

MAVeRiC-AD: Mixture-of-experts Agentic Vision-Language Ensemble for Robust MRI Classification of Alzheimer's Disease
Robust classification of Alzheimer's disease (AD) from structural T1-weighted MRI (T1w) images remains an unmet clinical need, especially when data is acquired at multiple sites that differ in scanning protocols and population demographics. In this paper, we present MAVeRiC-AD (Mixture-of-experts Agent-guided Vision-Language Ensemble for Robust Imaging-based classification of Alzheimer's Disease), an agentic framework that dynamically utilizes the optimal inferencing tool for radiological queries to provide relevant answers to the user. In our framework, we tested three specialized models encoded as callable tools: (1) CNN-AD, a 3D DenseNet trained on T1w intensities only; (2) MOE-VLM, a vision-language model that jointly models the T1w with subject-specific demographics (age, sex, site) via a mixture-of-experts (MoE) projection head; (3) Retrieval engine, a similarity-search module that contextualizes a patient against others from the site and reports % prevalence of AD. A light-weight agent analyzes the user request and then routes the input (image, or image + text) to the appropriate tool, aggregates responses and returns the tool response augmented with its confidence derived from conformal prediction. Experiments were conducted using T1w images from the ADNI (N=4,098) and OASIS-3 (N=600) datasets. Single-site training baselines achieved ROC-AUC = 0.79 (CNN) and 0.82 (VLM) on ADNI. When trained jointly on both sites, MOE-VLM surpassed both image-only and standard vision-language models with ROC-AUC = 0.90 on ADNI and 0.81 on OASIS. MAVeRiC-AD demonstrates that agentic orchestration of complementary expert deep models, coupled with explicit demographic conditioning for multi-site data can improve robustness and interpretability of AD image analysis pipelines and serves as a blueprint for scalable, trustworthy clinical AI assistants.

stk32a links sleep homeostasis to suppression of sensory and motor systems
Sleep is regulated by a homeostatic process and associated with an increased arousal threshold, but the genetic and neuronal mechanisms that implement these essential features of sleep remain poorly understood. To address these fundamental questions, we performed a zebrafish genetic screen informed by human genome-wide association studies. We found that mutation of serine/threonine kinase 32a (stk32a) results in increased sleep and impaired sleep homeostasis in both zebrafish and mice, and that stk32a acts downstream of neurotensin signaling and the serotonergic raphe in zebrafish. stk32a mutation reduces phosphorylation of neurofilament proteins, which are co-expressed with stk32a in neurons that regulate motor activity and in lateral line hair cells that detect environmental stimuli, and ablating these cells phenocopies stk32a mutation. Neurotensin signaling inhibits specific sensory and motor populations, and blocks stimulus-evoked responses of neurons that relay sensory information from hair cells to the brain. Our work thus shows that stk32a is an evolutionarily conserved sleep regulator that links neuropeptidergic and neuromodulatory systems to homeostatic sleep drive and changes in arousal threshold, which are implemented through suppression of specific sensory and motor systems.

Forebrain-specific loss of erythropoietin provokes compensatory upregulation of different EPO receptors
The procognitive growth factor erythropoietin (EPO) and its canonical receptor, EPOR, have long been recognized to be expressed by most cell types in the brain. Cognitive domains, improved by injections of exogenous EPO or by endogenous, hypoxia-stimulated EPO, include important forebrain functions, namely attention, working memory, drive, and executive performance. To gain mechanistic insight into the involvement of forebrain-expressed EPO, we deleted EPO in mice using as specific cre-driver Emx1. Here, we report that these mutant mice act comparably to their wildtype littermates in a comprehensive behavioral test battery. Importantly, we find that the transcripts of both EPOR and a novel, brain-expressed EPO receptor, EphB4, respond to EPO deletion with compensatory upregulation. EphB4 expression in brain and its increase upon forebrain erasure of EPOR are confirmed by in situ hybridization and immunohistochemistry. The augmented expression of both EPOR and EphB4 and their regulatory intercorrelation may explain why EmxEPO mutants show an even superior performance in the most challenging working memory task. Using the previously published single-nuclei-RNA-seq dataset, we further confirm the suggested compensatory mechanism, wherein EPO loss or reduction drives elevated EPOR expression, adding another layer to the intricate regulation of EPO signaling in hippocampal pyramidal neurons. Collectively, these data may explain the lack of behavioral and negative cognitive consequences upon forebrain-wide EPO elimination.

Perfect imperfections: seeking molecular and cellular asymmetries in the mouse brain
Although perfect symmetry is a mathematical ideal, many Bilateria exhibit left-right asymmetries of body, brain and behavior that are adaptive 1-3. In the human brain, various aspects of cognition are lateralized, including language 4 and handedness 5, which rely on left hemisphere dominance in most people. Brain hemispheric specialization can support parallel processing, neural efficiency, and action selection 3,6, while atypical structural or functional asymmetries are often found in neuropsychiatric disorders 7-10. Mice may be useful models for studying brain asymmetry because they show hemispheric differences of structure 11,12 and neurophysiology 13, but the extent to which molecular and cellular differences are involved remains unknown. We applied spatial transcriptomics with single molecule resolution to coronal sections from 31 adult mouse brains, to assess left-right differences of gene expression and cell types. Sections were chosen to capture the hippocampus and auditory cortex, as these two regions have shown the most prior evidence for functional asymmetry 13-15. In the hippocampus, Crhr1 (Corticotropin-Releasing Hormone Receptor 1) was more highly expressed in the pyramidal layers of CA1, CA3 and the dentate gyrus of the left hemisphere compared to the right. In the auditory cortex, three principal components capturing transcriptomic variation showed hemispheric differences, including prominent contributions from genes that have shown associations with human brain asymmetry. Overall cellular density and cell type proportions generally showed no significant hemispheric differences, with Car3 cortical excitatory neurons showing the most laterality. The transcriptional left-right differences that we found may relate to functional asymmetries for learning, memory and hearing.

Neural coding for tactile motion: Scanning speed or temporal frequency?
Humans effortlessly perceive the speed of an object moving across their fingers, but how the brain encodes this information, especially across the hierarchical stages in the primary somatosensory cortex, remains unclear. This study thus investigated coding schemes, including rate and temporal codes, for tactile motion speed in macaque S1 areas 3b, 1, and 2. Extracellular electrophysiology recorded single-unit activities when a rotating sinusoidal grating ball of a fixed spatial period (wavelength of 1, 2, or 4 mm) was presented on the fingerpad at various speeds (20-320 mm/s). The results showed that the rate code was commonly employed to differentiate the stimulus scanning speed, spatial period, and scanning direction across S1 regions. In contrast, the temporal code was used to faithfully represent the stimulus temporal frequency, which was defined as the speed divided by the spatial period. Notably, area 3b had a wider range of frequency responses than did areas 1 and 2. These findings demonstrate that S1 uses both rate and temporal codes to encode distinct aspects of tactile motion. Future research should investigate how temporal patterns in S1 neuronal activity are potentially transformed and utilized in downstream somatosensory areas to form tactile motion perception and guide perceptual decisions.

A low-cost and open-source olfactometer to precisely deliver single odours and odour mixtures
Olfaction has historically been the neglected sense, despite its profound influence on human emotion and memory, and its critical importance for animal behaviours including foraging, mating, and parenting. Perhaps contributing to this neglect is the fact that olfactory research has been hindered by technical challenges inherent to odour delivery: unlike visual or auditory stimuli, odorants must be vaporized, transported, and actively cleared, requiring specialized equipment and creating temporal delays and contamination risks. While commercial olfactometers provide reliable solutions for odour delivery, they are expensive and, due to proprietary software, difficult to customize. Existing custom designs, though excellent, may also be costly and/or require access to engineering workshops. To widen access to controlled odour delivery and hopefully encourage more labs to undertake olfactory research, we developed a low-cost, fully open-source olfactometer system requiring no specialized workshops or extensive engineering expertise. Our design prioritizes affordability, accessibility, and versatility while maintaining temporal precision and stimulus control and supporting diverse applications from rodent behavioural studies to human psychophysical investigations. In this methods article, which includes design specifications and assembly instructions as well as validation data, we aim to lower barriers to olfactory research and enable more laboratories to explore this fundamental sensory modality.

NMDA Receptor Kinetics Drive Distinct Routes to Chaotic Firing in Pyramidal Neurons
Neuronal firing patterns emerge from complex interactions between intrinsic membrane properties and synaptic receptor dynamics. N-methyl-D-aspartate (NMDA) receptors critically shape calcium influx and synaptic plasticity through their voltage-dependent Mg2+ block and prolonged activation kinetics. We developed a Hodgkin-Huxley-type computational model incorporating NMDA, AMPA, and GABA receptor kinetics to investigate how NMDA receptor closing rates (beta_NMDA) and glutamatergic stimulation frequency control neuronal dynamics. Systematic analysis of 2,942,093 inter-spike intervals across 1,961 parameter combinations revealed two mechanistically distinct pathways to firing irregularity. Pathway 1 involves rapid NMDA deactivation (beta_NMDA > 0.06 ms-1) at elevated stimulation frequencies, producing deterministic chaos with compromised information encoding (entropy: 1.441 bits, mutual information: 0.185 bits). Pathway 2 results from slow NMDA deactivation (beta_NMDA < 0.02 ms-1) under weak drive, creating irregularity through prolonged receptor activation and sustained calcium influx (entropy: 1.347 bits). An optimal kinetic window emerged at beta_NMDA = 0.028 ms-1, maximizing information transfer (0.275 bits) while maintaining stable dynamics. Entropy-Lyapunov correlation analysis confirmed deterministic chaos (r = 0.150, p < 0.001). Frequency-dependent chaos onset thresholds demonstrated systematic erosion from 0.000 ms-1 at low frequencies to 0.150 ms-1 at high frequencies. GABAergic inhibition provided frequency-selective stabilization, expanding stable parameter space by 34.2% while preserving gamma oscillations. CaMKII phosphorylation analysis revealed that prolonged NMDA activation maintains elevated phosphorylation levels (8.7 +/- 0.3 x 10-21 M vs. 1.8 +/- 0.1 x 10-23 M for normal kinetics), creating conditions for pathological long-term potentiation. These findings establish NMDA receptor kinetics as fundamental controllers of cortical excitability and information processing. The dual-pathway framework provides mechanistic insights into addiction-related memory formation, where prolonged NMDA activation enables pathological plasticity, and visual processing disorders, where altered kinetics disrupt retinal function and cortical oscillatory balance. The identification of optimal kinetic windows and frequency-selective GABA modulation suggests therapeutic strategies targeting kinetically-specific interventions for neuropsychiatric disorders involving NMDA dysfunction.

Individual olfactory channels shape distinct parameters of sleep architecture
Across the animal kingdom, olfactory dysfunction and anosmia have been associated with disruptions in sleep. In the fruit fly Drosophila melanogaster, various studies have demonstrated that broadly inhibiting olfactory receptor neurons (ORNs) similarly disrupts sleep/wake cycles, suggesting that baseline ORN signaling is an integral component of olfactory modulation of sleep. However, due to the diversity of ORNs and combinatorial nature of olfactory processing, many of the cellular and molecular mechanisms by which ORNs modulate sleep remain unclear. In this study, we addressed this gap of knowledge by characterizing the contributions of different ensembles of ORNs, individual ORN types, and a known modulator of ORNs on baseline sleep architecture. We find that the activity of distinct ORN types are important for day and nighttime sleep and heterogeneously shape parameters of sleep architecture. Importantly, the effects of ORN signaling on sleep are adjusted across mating status, suggesting that distinct ORN types are recruited within the context of sleep depending on the demands of the animal. Furthermore, the effects of ORN signaling on sleep are in part shaped by heterogeneous serotonin (5-HT) receptor expression. Together, this work identifies cellular and molecular pathways bridging olfaction and sleep, and helps establish a circuit model that can be used to further characterize the behavioral consequences of sensory dysfunction.

NeuronID: An automatic toolkit for identifying neurons in two-photon calcium imaging data
Two-photon calcium imaging has emerged as a powerful technique for monitoring neuronal activity in neuroscience; however, its data processing remains challenging. Here, we introduce NeuronID, an automatic toolkit designed to process two-photon calcium imaging data. The NeuronID toolkit features a modular architecture that includes motion correction, noise reduction, segmentation of neuronal components, and extraction of neuronal signals. Notably, the NeuronID toolkit offers an optimized strategy for segmenting neuronal components, which systematically integrates morphological boundary identification, cross-correlation analysis between pixels, and evaluation of neuronal signal quality. Compared to existing tools or manual annotation by experts, the NeuronID toolkit reduces the likelihood of over-segmentation while achieving near-human accuracy. Overall, this study provides a standardized analytical tool for processing two-photon calcium imaging data.

Enabling wider access to human molecular neuroscience research in pain: A simple preservation method for human dorsal root ganglion neurons in Hibernate A media
The use of human dorsal root ganglion (DRG) from organ donors opens the door for research into the molecular biology and physiology of human nociceptors; however, there are barriers to working with this tissue including logistical difficulties and limited access. We present an approach using Hibernate media to temporarily store either whole DRGs or dissociated DRG neurons prior to culturing and functional testing. Dissociation of DRGs following temporary storage (4-16hrs) in Hibernate media resulted in similar neuronal and immune cell yield as acutely dissociated DRGs. Neurons derived from DRGs stored in Hibernate media prior to dissociation exhibited similar electrophysiological properties and capsaicin responses as acutely dissociated DRG neurons. Similarly, neurons from acutely dissociated DRGs stored in Hibernate media (>24hrs) and shipped to geographically distant laboratories produced neuronal cultures displaying comparable electrophysiological properties as acutely cultured neurons. This approach overcomes insurmountable logistical burdens and increases access to freshly recovered human DRGs.

Unpredictable circadian rhythm disruption in Wistar rats: biological and behavioural changes reflecting bipolar disorder pathophysiology
Circadian disturbances are implicated in dysregulation of arousal and general neurobiological function, contributing to conditions such as bipolar disorder (BD). However, the behavioural and biological consequences of circadian disruption on arousal dysfunction remain poorly quantified. Here, we developed a novel unpredictable circadian disruption (UCD) protocol - consisting of unpredictable exposure to light and sound - to investigate its impact on locomotor activity and its association with metabolic, inflammatory, stress, and circadian markers in the nucleus accumbens (NAc). Forty-eight Wistar rats were exposed to UCD or control conditions, with or without corticosterone administration, for five weeks. Body weight was tracked throughout the study. Locomotor activity was assessed over the final two weeks (nine sessions) in an open-field arena. Real-time PCR was used to quantify NAc gene expression of inflammatory, metabolic, stress, and circadian markers, while liquid chromatography-mass spectrometry (LC-MS) measured neurotransmitter and central carbon metabolite concentrations. UCD animals exhibited initial hyperactivity at three weeks, followed by hypoactivity at four weeks. UCD was associated with increased NAc expression of inflammatory, stress, and circadian markers. Male UCD animals showed significant weight gain, an effect reversed in females. UCD also induced increases in NAc insulin resistance markers and reductions in central carbon metabolites, indicating disrupted striatal glucose metabolism. These findings highlight the central effects of circadian disruption on locomotor behaviour, stress, and immunometabolic signalling, offering mechanistic insights into arousal dysfunction in BD.

Alpha-synuclein overexpression reduces neural activity within a basal ganglia vocal nucleus in a zebra finch model
Vocal motor impairments, including changes in pitch, loudness, and timing are prevalent in Parkinsons Disease (PD) and a target for early intervention and treatment, yet the neural mechanisms underlying these impairments are not understood, motivating work in animal models. The adult male zebra finch songbird is uniquely poised for these studies given vocally-dedicated brain nuclei and a quantifiable output (birdsong). Our prior publication revealed that injection of an adeno-associated virus (AAV5) expressing the human (h) alpha-synuclein (hSNCA, a-syn) gene into basal ganglia vocal nucleus Area X results in higher levels of insoluble a-syn protein and changes reminiscent of human PD including softer, shorter, and reduced number of vocalizations compared to AAV5 controls. Here, we test the hypothesis that AAV-hSNCA overexpression reduces the firing rate of specific neuronal sub-types in Area X using in vivo recordings in anesthetized finches. Five classes of neurons were differentiated in AAV-treated finches based on waveform width (narrow vs. wide) and firing rates (low vs. fast). Wide-waveform/low-rate activity is a consistent feature of striatal medium spiny neurons (MSNs), a dominant cell type in Area X and in mammalian basal ganglia. Reduced firing rates and enhanced post-peak rebound were detected in the AAV-hSNCA group for putative MSN neurons compared to AAV controls. No differences in firing rate nor waveform shape were detected for the narrow waveform neurons. Our findings provide the first characterization of early a-syn-driven neural activity changes in vocal control neurocircuitry.

Intrinsic interval timing, not temporal prediction, underlies ramping dynamics in visual and parietal cortex
Neural activity following regular sensory events can reflect either elapsed time since the previous event (temporal signaling) or temporal predictions and prediction errors about the next event (temporal predictive processing). These mechanisms are often confounded, yet dissociating them is essential for understanding neural circuit computations. We addressed this by performing two-photon calcium imaging from distinct cell types (excitatory, VIP and SST) in layer 2/3 of visual and posterior parietal cortex (PPC), while awake mice passively viewed audio-visual stimuli under temporal contexts with different inter-stimulus interval (ISI) distributions. Computational modeling revealed distinct functional clusters of neurons, including stimulus-activated (ramp-down) and stimulus-inhibited (ramp-up) categories, with distinct kinetics and area/cell-type biases. Importantly, all functional clusters were invariant to temporal predictability, shifted immediately when temporal statistics changed, and were identical between naive and experienced mice. Population decoding revealed that clusters with heterogeneous kinetics differed in how well they represented interval information, such that together they tiled elapsed time and produced a distributed, learning-independent population code for time. These results provide strong evidence against temporal predictive processing in V1/PPC under passive conditions and instead demonstrate intrinsic coding of interval timing, redefining the mechanistic origin of ramping and omission-related activity in sensory cortex. We discuss how these dynamics align with stimulus-reset attractor frameworks, and propose that temporal predictive processing is more likely implemented in other circuits or recruited in V1/PPC during task-engaged behavior.

A common neural architecture for encoding finger movements
Finger tapping is widely used to investigate sensorimotor brain responses, yet it remains unclear whether shared neural codes for complex finger movements exist across individuals, given the highly individual-specific topography of the sensorimotor cortex. We combined spherical searchlight Procrustes hyperalignment on 7-Tesla fMRI data with between-subject classification to investigate the existence of a shared latent neural architecture encoding sequential finger movements in the human sensorimotor cortex. Our model afforded above-chance level accuracy in both the contralateral and ipsilateral areas, suggesting that such a high-dimensional neural information space exists, is traceable, and spreads over the sensorimotor cortex. Critically, these high-dimensional neural codes were identified without task-specific training and cannot be attributed to error-related activity. These findings establish universal organizational principles of motor sequence encoding and pave the way for personalized neurotechnologies, scalable brain-computer interfaces, and cross-subject models for motor learning and rehabilitation.

Cerebellar growth is associated with domain-specific cerebral maturation and socio-linguistic behavioral outcomes
The cerebellum's involvement in cognitive functions is increasingly recognized, yet its developmental contribution to cognition remains poorly understood. The cerebellum undergoes rapid development in early life, paralleling major cognitive and behavioral changes. Although clinical studies have linked early cerebellar disruptions to profound developmental deficits, it remains largely unclear how typical cerebellar maturation supports the development of cognitive functions and how it interacts with broader brain development. Here, we apply a normative modeling framework to map cerebellar volumetric growth from infancy to young adulthood (N = 751; ages 1-21 years). Using lobular and functional cerebellar parcellations, we comprehensively characterize typical cerebellar development and examine how it aligns with cerebral development and behavioral outcomes. Across parcellations, posterior higher association areas consistently show steeper growth trajectories than anterior sensorimotor areas. Cerebellar and cerebral areas with similar functional roles demonstrate coordinated maturation, and volumetric growth in the posterior cerebellum relates to individual differences in socio-linguistic behaviors. These findings establish a comprehensive reference for typical cerebellar development, highlight cerebellar co-maturation with the cerebral cortex, and underscore the cerebellum's role in supporting emerging higher cognitive functions.

Infant Brains Tick at 4Hz - Resonance Properties of the Developing Visual System
Neural rhythms of the infant brain are not well understood. Testing the rhythmic properties of the adult visual system with periodic or broadband visual stimulation elicited neural resonance phenomena at ~10Hz alpha rhythm. Here, we extend this approach to reveal the inherent rhythmic properties of the infant brain. Eight-month-olds (N = 42) were presented with visual stimuli flickering at discrete frequencies (2, 4, 6, 8, 10, 15, 20, and 30Hz) and broadband (i.e., aperiodic) stimulation, while recording a high-density electroencephalogram (EEG). As predicted, infants' visual system entrained to the harmonics of the periodic stimulation frequencies (first to third). In addition, a 4Hz rhythm emerged independent of stimulation frequency. Critically, the impulse response function (IRF) of the broadband sequence revealed a perceptual echo of visual information at 4Hz. This echo lasted for about 1 second (i.e. four cycles), extended into frontal sensors, and selectively resonated the 4Hz component of the input signal. In a complementary adult assessment, we confirm an alpha response upon periodic and broadband stimulation in the present paradigm for the mature visual system. To conclude, perturbing the infant visual system elicited a neural response and resonant activity at the 4Hz theta rhythm, which contrasts with the 10Hz alpha rhythm found in the adult visual system. Neural processing dynamics are thus essential to understand early brain development in full.

Characterization of the central sulcus pli-de-passage fronto-parietal moyen in > 1000 human brains
The pli-de-passage fronto-parietal moyen (PPfpm), a deep cerebral fold of the human brain, presents as a common though small elevation at the central sulcus (CS) fundus where it connects the pre- and postcentral gyri at the level of the sensorimotor hand area. Given the PPfpm's location, single case-reports of its association with the functional sensorimotor hand area, and evidence linking it to the somato-cognitive action network, it holds potential as an anatomical landmark for the sensorimotor region. To characterize the macroscopic morphology of the PPfpm and evaluate its relevance as a reliable and easily detectable anatomical landmark, methods for observer-independent characterization of cortical sulci and structures were adapted and developed to investigate the PPfpm in a large dataset. For 1112 subjects from the Human Connectome Project Young Adult S1200 Release, CS depth profiles were computed from structural magnetic resonance imaging (MRI) data, and an algorithm was developed to automatically extract the PPfpm from these depth profiles. Based on the extraction of two key features approximating the PPfpm at its peak height (PPfpm-I) and its lateral end (PPfpm-II), a principal description of the PPfpm's position and extent as influenced by hemisphere and sex was conducted. Analyses revealed the PPfpm as a near-universal cerebral fold in the adult human brain, consistently located at mid-height within the CS with a strong association to the CS sulcal pits. Though commonly of a small extent, the PPfpm can be reliably identified in CS depth profiles and in structural MRI data. By providing a systematic, modern macroanatomical characterization of the PPfpm in a large cohort with rigorous quality control, the present study demonstrates the potential of the PPfpm to serve as a robust anatomical landmark for the sensorimotor hand area of the human brain.

Resolving the estrogen paradox in hereditary retinal degeneration: Esr1 activation suppresses Tnf-α signaling as a photoreceptor self-protection mechanism
Retinitis pigmentosa (RP) is an inherited retinal degenerative disorder characterized by progressive photoreceptor loss and irreversible blindness. Increasing evidence implicates neuroinflammation as a contributor to photoreceptor degeneration extending beyond the initial genetic insult. Although estrogen has been reported to exert anti-inflammatory effects in the central nervous system, its role in RP remains controversial, with some studies suggesting a paradoxical exacerbation of retinal pathology. To address this discrepancy, we identify estrogen receptor alpha (Esr1) as a central immunoregulatory hub in RP. Transcriptomic analyses of rd1 and rd10 revealed upregulation of estrogen-responsive and inflammatory pathways, with Esr1 expression markedly elevated during degeneration. TUNEL assays demonstrated that systemic estradiol (E2) exerted divergent effects, protective in rd1 yet deleterious in rd10, whereas selective pharmacological activation of Esr1 with propyl pyrazole triol (PPT) consistently reduced photoreceptor death, preserved dark-adapted ERG responses, and downregulated inflammatory mediators including Tnf-, Cx3cl1/Cx3cr1, Cd68, and Iba1. Mechanistically, Esr1 activation repressed microglial Tnf transcription and disrupted a self-sustaining Cx3cl1/Cx3cr1-Tnf- signaling loop driving microglial recruitment, activation and neurotoxicity in the outer nuclear layer (ONL). Targeted interventions confirmed tumor necrosis factor receptor 1 (Tnfr1) as the principal mediator of Tnf-induced photoreceptor death: selective inhibition with R7050 conferred superior protection compared with broad-spectrum Tnf- inhibitors (etanercept, infliximab). Cx3cr1 blockade likewise suppressed microglial activation and improved visual outcomes. Collectively, our findings establish Esr1 activation as not merely an external intervention but the amplification of an intrinsic self-protective program, positioning Esr1, Tnfr1, and Cx3cr1 as actionable therapeutic targets to suppress neuroinflammation and preserve vision in RP and related retinal disorders.

Test-retest reliability of sensorimotor activity measured with spinal cord fMRI
Establishing the reliability of spinal cord functional magnetic resonance imaging (fMRI) is critical before employing it to assess experimental or clinical interventions. Previous studies have mapped human motor activity primarily to the ipsilateral ventral horn, aligning with myotomal and dermatomal projections. Despite these insights, the test-retest reliability of spinal fMRI remains under-investigated. Here we assessed spinal cord activation during a sensorimotor paradigm involving right-hand grasping and grip force estimation in 30 healthy volunteers. Participants completed two identical scanning visits, each time performing the same task twice, enabling the investigation of test-retest reliability both within a single experimental visit and between visits performed on different days. Aggregating all task runs, motor-evoked activation was observed in ipsilateral ventro-dorsal regions of spinal segmental levels C6-C8 and T2, as well as in medial regions of levels C1-C3. Despite highly reliable task performance (grip force) and fMRI signal quality (temporal signal-to-noise ratio), the reliability of motor activation was predominantly poor both within and between visits, with notable variability in spatial distribution observed across task runs. Increasing the number of task runs per individual improved the robustness of group-level activation, as indexed by higher activated voxel count, larger cluster spatial extent, and attenuated t-statistic distribution. Although we demonstrated that motor-evoked activation corresponds to the known neuroanatomical organisation of motor circuits, its low test-retest reliability presents a challenge for wider applications of spinal fMRI. Understanding the drivers of low reliability in functional imaging is warranted, but we suggest that looking beyond measurement error is required, including careful consideration of inherent within-individual variability underpinned by neurophysiological and psychological factors.

Representational Geometries of Perception and Working Memory: A Pilot Study
This study aims to compare the neural representational geometry of visual perception and visual working memory using human fMRI. In our pilot experiment, observers viewed a face-scene blended image (sample) and selectively attended to either the face or scene aspects of the sample. They then judged whether the attended aspects were the same as or different from that of the subsequent test image. In three out of four observers, we found that the coding axis, which distinguishes faces and scenes, was rotated when perceptual content transforms into working memory, not only in the visual cortex but also in some higher association cortical areas. In these regions, exclusive combinations (i.e., perceived face and memorized scene vs. perceived scene and memorized face) were successfully classified by linear decoders, indicating that perception and working memory are represented in partially distinct subspaces. Such specific coding may help prevent confusion between perception and memory. Meanwhile, however, cross-decoding of visual contents across perception and working memory was also robust, indicating common coding components between them. Such common coding may help to explain why even though we generally have no difficulty in distinguishing working memory content from perceptual content, there is yet a sense in which their contents are qualitatively similar. Hereby, we pre-register the hypotheses, experimental design, analysis plan, and stopping rule for data collection before examining whether these preliminary results can be replicated in a larger sample.

Decoding Spine Nanostructure in Mental Disorders Reveals a Schizophrenia-Linked Role for Ecrg4
Dendritic spine dysfunction may contribute to the etiology and symptom expression of neuropsychiatric disorders. The intimate relationship between spine morphology and function suggests that decoding disease-related abnormalities from spine morphology can aid in developing synapse-targeted interventions. Here, we describe a population analysis of dendritic spine nanostructure applied to the objective grouping of multiple mouse models of neuropsychiatric disorders. This method has identified two major groups of spine phenotypes linked to schizophrenia and autism spectrum disorder (ASD). An increase in spine subpopulation with small volumes characterized the spines of schizophrenia mouse models, whereas a spine subset with large volumes increased in ASD models. Schizophrenia mouse models showed higher similarity in spine morphology, which was caused by a reduced speed of nascent spine growth. The expression of Ecrg4, a gene encoding small secretory peptides, was increased in schizophrenia mouse models, and functional studies confirmed its critical involvement in impaired spine dynamics and shape in schizophrenia mouse models. These results suggest that the population-level spine analysis provides rich information about the heterogeneous spine pathology, which facilitates identification of new molecular targets related to core synaptic dysfunction.

Bidirectional modulation of sleep and wakefulness via prefrontal cortical chemogenetics
The drive to sleep is inescapable but its biological substrate remains largely elusive. Until recently, the search for sleep centres in the mammalian brain focussed on subcortical neurons that promote sleep or wakefulness, or induce state transitions. However, the regulatory elements of mammalian sleep circuitry, which govern the timing, amount and intensity of sleep, have proven difficult to elucidate. Growing evidence suggests an essential role for the cerebral cortex. Here we used a chemogenetic approach to test whether prefrontal cortex (PFC) layer 5 pyramidal neurons partake in the regulation of sleep. We found that inhibiting or exciting Rbp4-Cre neurons in the PFC with hM4Di/hM3Dq Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) increases and decreases sleep, respectively. Targeted PFC DREADD inhibition of Rbp4-Cre neurons induces sleep that electrophysiologically and architecturally resembles spontaneous sleep. In contrast, widespread cortical DREADD inhibition induces sleep that is punctuated by frequent brief awakenings, has suppressed rapid-eye-movement (REM) sleep, and is followed by a rebound in electroencephalogram (EEG) slow wave activity (SWA), typically observed after disrupted or lost sleep. Our work demonstrates that local modulation of cortical activity can bidirectionally change the amount of global sleep. This represents an important step in the dissection of sleep circuitry, aids the identification of molecular counterparts of sleep pressure, and accelerates the delineation of top-down sleep-regulatory pathways. Together, these lay the foundation for neurobiologically-informed sleep treatments, such as targeted non-invasive brain stimulation and cell-type specific pharmaceuticals, to better modulate sleep in humans.

Localized Space Coding and Phase Coding Complement Each Other to Achieve Robust and Efficient Spatial Representation
Localized space coding and phase coding are two distinct strategies responsible, respectively, for representing abstract structure and sensory observations in neural cognitive maps. In spatial representation, localized space coding is implemented by place cells in the hippocampus (HPC), while phase coding is implemented by grid cells in the medial entorhinal cortex (MEC). Both strategies have their own advantages and disadvantages, and neither of them meets the requirement of representing space robustly and efficiently in the brain. Here, we show that through reciprocal connections between HPC and MEC, place and grid cells can complement each other to overcome their respective shortcomings. Specifically, we build a coupled network model, in which a continuous attractor neural network (CANN) with position coordinate models place cells, while multiple CANNs with phase coordinates model grid cell modules with varying spacings. The reciprocal connections between place and grid cells encode the correlation prior between the sensory cues processed by HPC and MEC, respectively. Using this model, we show that: 1) place and grid cells interact to integrate sensory cues in a Bayesian manner; 2) place cells complement grid cells in coding accuracy by eliminating non-local errors of the latter; 3) grid cells complement place cells in coding efficiency by enlarging the number of environmental maps stored stably by the latter. We demonstrate that the coupled network model explains the seemingly contradictory experimental findings about the remapping phenomena of place cells when grid cells are either inactivated or depolarized. This study gives us insight into understanding how the brain employs collaborative localized and phase coding to realize both robust and efficient information representation.

Cross-species brain circuitry from diffusion MRI tractography and mouse viral tracing
We integrate tracer-derived projection polarity from ~1,200 mouse injections with species-specific diffusion MRI (dMRI) tractography to construct directed connectomes for mouse, marmoset, rhesus macaque, and human. We model brain circuitry as a directed connectome, in which asymmetric pathways capture the forward flow of neuronal signals. Using a common cross-species atlas as a scaffold, we introduced a multi-objective path efficiency metric that weighs projection strength against axonal length and applied directed shortest-path algorithms to quantify inter-regional influence. This framework revealed both conserved and divergent organization: the entorhinal-hippocampal projection remained the most efficient in all species, while humans exhibited strengthened temporal-insula-frontal circuits and reduced olfactory influence, rhesus macaques showed peak efficiencies in inferior temporal outflows, and marmosets maintained high olfactory influence. Together, these results establish a scalable approach for constructing directed connectomes across species and demonstrate how conserved and lineage-specific circuits jointly shaped association and sensory systems.

Not two sides of the same coin: Divergent effects of motor state on corticospinal and cortical responses to TMS of motor cortex
Background: Transcranial magnetic stimulation (TMS) of the motor cortex can elicit motor evoked potentials (MEPs) in target muscles, reflecting corticospinal excitability. MEP amplitudes increase with TMS intensity and can be facilitated by tonic muscle pre-activation. Since conventional transcranial evoked potentials (TEPs) also grow with increasing TMS intensity, cortical and corticospinal responses are often considered two facets of the same process. If this were true, changes in physiological motor state should modulate TEPs and MEPs in a similar manner. Methods: To compare the state-dependency of cortical and corticospinal responses to single-pulse TMS, we simultaneously recorded TEPs and MEPs in 16 healthy young adults during relaxation and isometric contraction of the right first dorsal interosseous (FDI) muscle. For each condition, 100 biphasic TMS pulses were delivered to the left primary motor hand area at five different intensities centered around the resting motor threshold. Results: TEP and MEP amplitudes increased with stimulation intensity. As predicted, tonic muscle contraction consistently facilitated MEP. On the contrary, muscle contraction attenuated two key peaks of the TEP (N15 and N100). The state-dependent effects of corticospinal and cortical responses were not correlated. Discussion: Both TEPs and MEPs are reliably modulated by motor state, yet they differ in direction and their magnitudes do not scale with each other. These findings challenge the assumption that cortical and corticospinal responses are two aspects of the same process. MEP facilitation during contraction likely reflects increased spinal excitability, whereas TEP attenuation may reflect reduced responsiveness of cortico-cortical or cortico-subcortical networks.

Effective connectivity of the human claustrum: Triple networks, subcortical circuits and psychedelic modulation
Decades of cross-species research highlight the claustrums extensive bidirectional connectivity with cortical and subcortical regions, implicating it in higher-order cognitive processes requiring synchronized brain states. Psychedelics may disrupt this synchrony by modulating claustro-cortical signaling, reflected by the dissolution of cortical network signatures. Using spectral dynamic causal modeling on resting-state fMRI data from the Human Connectome Project and PsiConnect datasets at 7T and 3T, we provide the first in vivo characterization of claustral effective connectivity with triple networks and subcortical regions in humans, both at rest and under the influence of psilocybin. Claustra displayed widespread bidirectional effective connectivity and a strong inhibitory influence on all target regions. Psilocybin enhanced claustral inhibition of cortical networks while disinhibiting subcortical areas, partially associated with psychedelic subjective effect scores. These findings are consistent with cellular and functional cross-species data, supporting the proposed mechanism of claustro-cortical inhibition in regulating network synchrony, while extending this influence to the subcortex, and revealing hierarchical and hemispheric asymmetries in claustral signaling modulation under psilocybin.

Immunometabolic state modulation of sequential decision making in patch-foraging mice
Animals have evolved sophisticated behavioural and metabolic adaptations to respond to threats to homeostasis, including resource scarcity and infectious pathogens. Energy deficits associated with lack of food availability and sickness-associated anorexia elicit distinctive hypometabolic states, however how such states are integrated with higher-order cognition is largely unknown. Patch-foraging paradigms have proven useful for deciphering evolutionarily conserved and ethologically grounded insights into cost-benefit decision-making as animals continually deliberate between exploiting and exploring their environment. We developed and extensively validated a touchscreen-based patch-foraging task for mice in which food reward dynamically varied across trials, in a dataset comprising over 111,000 sequential decisions from 35 adult male mice. Contrary to predictions that emphasize the impact of inflammation to blunt effortful reward-driven behaviour, our results demonstrate that systemic lipopolysaccharides-induced inflammation promotes hyper-exploitation by attenuating exploratory choice behaviour in animals interacting with complex food environments. Such behaviour can be seen as a bias towards immediate outcomes, with impulsivity as a feature affecting the weighting of temporal factors. Given the ubiquity of systemic inflammation in numerous infectious, metabolic and psychiatric disorders featuring dysfunctional value- and cost-sensitive behaviour, these results provide insight into how immunometabolic states are linked to altered decision-making.

A unified model of cortico-hippocampal interactions through neural field theory
Functional interactions between cortex and hippocampus play a central role in cognition and are disrupted in major neurological disorders, but the mechanisms underlying coordinated cortico-hippocampal dynamics are poorly understood. We address this challenge using neural field theory, a biophysically-grounded framework for modelling large-scale neural dynamics. We first show how the autonomous activity of cortex and hippocampus emerge from corticothalamic and hippocampo-septal feedback loops, respectively, giving rise to cortical alpha and hippocampal theta rhythms. We next integrate these two systems through topologically and topographically informed coupling between cortex and hippocampus. Weak coupling yields spatially precise correlations between cortical and hippocampal activity, consistent with neurophysiological recordings. Stronger coupling pushes both the cortex and the hippocampus toward criticality, triggering state transitions and mode mixing, such that activity propagates across spatial scales and reorganizes both cortical and hippocampal dynamics. These disruptive, unstable processes also provide an explanation for the frequent involvement of the hippocampus in seizures. This prediction is validated using intracranial electroencephalographic data from human patients with focal onset epilepsy. Together, these results establish a geometrically and biophysically grounded framework that gives a unifying account of large-scale cortico-hippocampal dynamics and provides a physically principled foundation for studying other distributed brain systems.

Change in motor state equilibrium explains prokinetic effect of apomorphine on locomotion in experimental Parkinsonism
Gait impairments remain an unresolved challenge in Parkinson's disease (PD). Clinical studies highlight the importance of neural oscillations underlying motor deficits. Yet, how dopaminergic medication impacts brain activity for gait therapy remains poorly understood. To address this issue, we explored the influence of apomorphine on cortical oscillations during self-initiated locomotion on a runway in the unilateral 6-OHDA rat model of PD. In this task, deficits are characterized by slow movements and repeated interruptions of the gait sequence. Our results show that apomorphine reduced akinesia, increased voluntary transitions to gait, and prolonged individual gait bouts leading to an overall increase in the travel distance on the runway. In contrast, kinematic analysis revealed that these prokinetic changes were accompanied by a reduction in leg velocity and step length. At the neural level, behavioral changes correlated with a shift from beta and low-gamma to high-gamma brain rhythms. Beta and low-gamma significantly correlated with reduced transitions to gait, while high-gamma lead to a shift away from akinesia to prokinetic motor states. Together, our results provide new insights into the cortical regulation of locomotion and reveal the potential of apomorphine to differentially regulate gait sequence execution and gait kinematics. We propose that the prokinetic effects of apomorphine are best explained by the concept of a motor state equilibrium that is defined by the observable motor states, their durations and number of state transitions. This concept provides a simplified representation of complex treatment effects and holds promise to improve data interpretation for clinical translation.

Neurodegeneration emerges at a cellular tipping point between protein accumulation and removal.
Protein aggregates are a hallmark of pathology across neurodegenerative diseases. Yet, the disconnect between molecular- level aggregation and the emergence of disease severely limits mechanistic understanding of neurodegeneration. Here, we bridge this disconnect by showing that a cellular tipping point emerges as a universal feature across diseases from the competition between aggregate accumulation and removal. We map the resulting cellular phase transition with our high-throughput live-cell assay, measuring the tipping point that separates healthy cells from those burdened with large aggregate loads. Using super-resolution imaging of brain tissue from Alzheimer's and Parkinson's disease, we quantify how the crucial balance of accumulation and removal is shifted in disease. Combined with in vitro aggregation kinetics, we then validate our framework by predicting how designed aggregation inhibitors shift the tipping point to restore cellular homeostasis. Our results provide a mechanistic framework to connect molecular-level aggregation to disease states, paving the way for a quantitative, unified understanding of neurodegeneration and enabling predictions of the complex, non-linear dynamics that govern therapeutic efficacy.

Capturing instantaneous neural signal-behavior relationships with concurrent functional mixed models
We previously proposed an analysis framework for fiber photometry data based on functional linear mixed models (FLMMs). Functional LMMs allow modeling associations between photometry traces and trial-specific scalar values like behavioral summaries and session number, while also accounting for between-animal heterogeneity. Here, we extend the method to concurrent FLMMs (cFLMMs), a method that can fit the instantaneous relationship between functional outcomes and functional covariates. Concurrent FLMMs enable testing of how the photometry signal is associated with, for example, a behavioral variable that evolves across within-trial timepoints (e.g. animal speed). cFLMMs can also model the relationship between the photometry signal and covariates in experiments with variable trial lengths (e.g., in studies where trials end when an animal responds). We illustrate the application of cFLMMs on two published studies and show the method can identify signal-behavior associations in analyses not possible with FLMMs. We find that analyzing photometry-behavior associations based on behavioral summaries (e.g., latency-to-response, average lick rate) can lead to misleading conclusions. We published our method in the fastFMM package, available as an R package through GitHub (https://github.com/awqx/fastFMM).