bioRxiv Subject Collection: Neuroscience's Journal

A comprehensive chemotyping and gonadal regulation of seven kisspeptinergic neuronal populations in the mouse brain
Herein, we present a systematic analysis, using dual and multiplex RNAscope methods, of seven kisspeptinergic neuronal populations, based on their chemotyping and distribution throughout the mouse brain. The co-expression of mRNAs coding for neuropeptides, for excitatory and inhibitory transmitter biosynthetic enzymes, and for sex steroid receptors are described in four hypothalamic and three extra-hypothalamic nuclei. These include a newly characterized kisspeptin-expressing ventral premammillary nucleus cell group co-expressing vesicular glutamate transporter 2, pituitary adenylate cyclase-activating polypeptide and neurotensin mRNAs. Kisspeptin mRNA (Kiss1) was observed within both somatic and dendritic compartments at a single-cell level in two hypothalamic sites, a prominent and previously undescribed feature of kisspeptin neurons in these two cell groups. Patterns of altered Kiss1 expression following gonadectomy among these seven KP populations suggest that androgen receptor signaling may also play a previously unremarked role in gonadal feedback regulation of kisspeptinergic neuronal function. Data from this study provide a chemoanatomical basis for hypothesis generation regarding the functional diversity of kisspeptinergic signaling in hypothalamic and extrahypothalamic brain.

Differentiation of Acute Disseminated Encephalomyelitis from Multiple Sclerosis Using a Novel Brain Lesion Segmentation and Classification Pipeline
Multiple Sclerosis (MS) is a chronic autoimmune disease affecting the central nervous system, while Acute Disseminated Encephalomyelitis (ADEM) is a sudden, often monophasic inflammatory condition of the brain and spinal cord. Only 17% of ADEM cases are correctly diagnosed on the first visit due to overlapping clinical and radiological presentations with Multiple Sclerosis (MS) [1]. Both ADEM and MS are demyelinating diseases, meaning they cause brain lesions by damaging the myelin sheath, leading to scar tissue that disrupts nerve signals [2]. Previous machine learning pipelines have differentiated Neuromyelitis Optica Spectrum Disorder (NMOSD) (a different demyelinating disease) from MS and ADEM from NMOSD based on MRI imagery with varying accuracies [3, 4]. Our novel Classifier for Demyelinating Disease (CDD) pipeline is the first to differentiate ADEM from MS using MRI imagery. It does this in two stages: a segmentation stage which creates segmentation masks of the lesions and a classification stage to classify them as either ADEM or MS. Additionally, we introduce a novel ADEM dataset from open-access medical case reports. The CDD pipeline achieves an accuracy of 90.0% on our validation dataset, making it a potentially viable diagnostic tool in the future. All data and code is available here. 2

Effects of working memory training on cognitive flexibility, dendritic spine density and long-term potentiation in female mice
Working memory (WM) is a cognitive function that refers to the ability of short-term storage and manipulation of information necessary for the accomplishment of a task. Two brain regions involved in WM are the prefrontal cortex (PFC) and the hippocampus (HPC). Several studies have suggested that training in WM (WMT) can improve performance in other cognitive tasks. However, our understanding of the neurobiological changes induced by WMT is very limited. Previous work from our lab has shown that WMT enhances synaptic and structural plasticity in the PFC and HPC in male mice. In this study, we investigate the effect of WMT on cognitive flexibility and synaptic properties in PFC and HPC in adult female mice. To this end, female adult mice were split into 3 groups: a) naive which remained in their home cage, b) non-adaptive which learned to alternate the arms in the T-maze but without any delays and c) adaptive which were trained in the delayed alternation task for 9 days. The delayed alternation task was used for WMT. In one cohort, following the delayed alternation task, all mice were tested in the attention set-shifting (AST) task in order to measure cognitive flexibility, and then, the brains were harvested for Golgi-Cox staining to study dendritic spine density. Our results showed that in female mice, there were no differences in performance in the AST among the three groups tested, however, the latency to make a choice was reduced. With regards to dendritic spine density, no significant differences were identified in PFC while increased dendritic spine density was found in the hippocampus of the adaptive group, compared to the naive group. In a second cohort, acute brain slices were prepared following the delayed alternation task to investigate the synaptic properties in the PFC and the HPC. Evoked field excitatory post-synaptic potential (fEPSP) recordings were performed in either PFC or HPC brain slices. Our results show that tetanic-induced long-term potentiation (LTP) in the PFC was not different among the three training groups. In the HPC, theta-burst induced LTP was significantly increased in the adaptive group also compared to the other two groups. These results reveal both similarities and differences of WMT on cognitive flexibility, dendritic spine density and LTP in females, compared to males.

Neuron-specific partial reprogramming in the dentate gyrus impacts mouse behavior and ameliorates age-related decline in memory and learning.
Age-associated neurodegenerative disorders represent significant challenges due to progressive neuronal decline and limited treatments. In aged mice, partial reprogramming, characterized by pulsed expression of reprogramming factors, has shown promise in improving function in various tissues, but its impact on the aging brain remains poorly understood. Here we investigated the impact of in vivo partial reprogramming on mature neurons in the dentate gyrus of young and aged mice. Using two different approaches: a neuron-specific transgenic reprogrammable mouse model and neuron-specific targeted lentiviral delivery of OSKM reprogramming factors, we demonstrated that in vivo partial reprogramming of mature neurons in the dentate gyrus, a neurogenic niche in the adult mouse brain, can influence animal behavior, and ameliorate age-related decline in memory and learning. These findings underscore the potential of in vivo partial reprogramming as an important therapeutic intervention to rejuvenate the neurogenic niche and ameliorate cognitive decline associated with aging or neurodegeneration.

A Mathematical Sequence Representing Tonic Action Potential Spike Trains
This is a study on the regularity of action potential spikes. Through a stochastic study, we found a series of strong correlations between the intervals of tonically firing spikes with the existence of spike frequency adaptation generated by injecting constant currents of varying intensities into layer 5 pyramidal neurons of the ferret medial prefrontal cortex. Based on this, we derived a relationship formula for the interspike intervals (ISIs). According to this formula, an ISI can be expressed as a product of the first ISI and a mathematical sequence that factorials the history of all previous ISIs. When this formula was applied to individual neurons, the sequence part exhibited minimal variation in value against the intensity of stimulation and was similar across injected current intensities, serving as a precursor to timing which is related to spike number rather than time after stimulation. In contrast, the first ISI decreased negative logarithmically with the intensity of injected current, acting as a scale factor. Finally, we successfully predicted the timing of spike occurrences based on the characteristics of this sequence formula and replicated spike train generated by strong stimulation using partial information from spike trains generated by weak stimuli.

Longevity or Well-being? A Dual-Dimension Structure of Neuroticism
The development of personality traits is often viewed as evolutionarily adaptive. Current neuroticism research, however, predominantly highlights its negative health impacts, neglecting its potential evolutionary advantages. We propose that neuroticism's inter-individual variability can be structured into two distinct geometric dimensions. One, named the Emotional Reactivity-Instability/Distress Spectrum (ERIS), correlates strongly with longevity and is associated with chronic diseases and risk-averse lifestyle. This dimension is underpinned by evolutionarily conserved subcortical brain regions and genes. The other, resembling the overall neuroticism score, is primarily linked to mental and stress-related disorders, as well as life satisfaction. It involves higher-order emotional brain regions and is genetically enriched in human-accelerated regions. Collectively, these dimensions represent a dual-strategy personality framework that optimizes survival and well-being, with the former being evolutionarily conservative and the latter potentially an unique human adaptation.

Neural correlates of phonetic categorization under auditory (phoneme) and visual (grapheme) modalities
We tested whether the neural mechanisms of phonetic categorization are specific to speech sounds or generalize to graphemes (i.e., visual letters) of the same phonetic label. Given that linguistic experience shapes categorical processing, and letter-speech sound matching plays a crucial role during early reading acquisition, we hypothesized sound phoneme and visual grapheme tokens representing the same linguistic identity might recruit common neural substrates, despite originating from different sensory modalities. Behavioral and neuroelectric brain responses (ERPs) were acquired as participants categorized stimuli from sound (phoneme) and homologous letter (grapheme) continua each spanning a /da/ - /ga/ gradient. Behaviorally, listeners were faster and showed stronger categorization of phoneme compared to graphemes. At the neural level, multidimensional scaling of the EEG revealed responses self-organized in a categorial fashion such that tokens clustered within their respective modality beginning ~150-250 ms after stimulus onset. Source-resolved ERPs further revealed modality-specific and overlapping brain regions supporting phonetic categorization. Left inferior frontal gyrus and auditory cortex showed stronger responses for sound category members compared to phonetically ambiguous tokens, whereas early visual cortices paralleled this categorical organization for graphemes. Auditory and visual categorization also recruited common visual association areas in extrastriate cortex but in opposite hemispheres (auditory = left; visual=right). Our findings reveal both auditory and visual sensory cortex supports categorical organization for phonetic labels within their respective modalities. However, a partial overlap in phoneme and grapheme processing among occipital brain areas implies the presence of an isomorphic, domain-general mapping for phonetic categories in dorsal visual system.

Different Roles of D1/D2 Medium Spiny Neurons in the Nucleus Accumbens in Pair Bond Formation of Male Mandarin Voles
The mesolimbic dopamine (DA) system has been implicated in pair bond formation. However, involvements of DA release, real time activities, and electrophysiological activities of D1/D2 medium spiny neurons (MSNs) in the nucleus accumbens (NAc) shell in pair bonding remain unclear. This work verified that male mandarin voles after pair bonding released higher levels of DA in the NAc shell and displayed higher levels of D1 MSNs activity and lower levels of D2 MSNs activity upon sniffing their partners compared to upon sniffing an unknown female. Moreover, pair bonding induced differential alterations in both synaptic plasticity and neuronal intrinsic excitability in both D1 MSNs and D2 MSNs. In addition, chemogenetic inhibition (activation) of ventral pallidum-projecting D2 MSNs in the NAc shell enhanced (inhibited) pair bond formation, respectively. These findings suggest that different neuronal activity of NAc shell D1 MSNs / D2 MSNs regulated by increasing DA release after pair bonding may be a neurobiological mechanism underlying pair bond formation.

Overlapping Cortical Substrate of Biomechanical Control and Subjective Agency
Every movement requires the nervous system to solve a complex biomechanical control problem, but this process is mostly veiled from one's conscious awareness. Simultaneously, we also have conscious experience of controlling our movements - our sense of agency (SoA). Whether SoA corresponds to those neural representations that implement actual neuromuscular control is an open question with ethical, medical, and legal implications. If SoA is the conscious experience of control, this predicts that SoA can be decoded from the same brain structures that implement the so-called "inverse kinematic" computations for planning movement. We correlated human fMRI measurements during hand movements with the internal representations of a deep neural network (DNN) performing the same hand control task in a biomechanical simulation - revealing detailed cortical encodings of sensorimotor states, idiosyncratic to each subject. We then manipulated SoA by usurping control of participants' muscles via electrical stimulation, and found that the same voxels which were best explained by modeled inverse kinematic representations - which, strikingly, were located in canonically visual areas - also predicted SoA. Importantly, model-brain correspondences and robust SoA decoding could both be achieved within single subjects, enabling relationships between motor representations and awareness to be studied at the level of the individual.

CD2AP is Co-Expressed with Tropomyosin-Related Kinase A and Ras-Related Protein Rab-5A in Cholinergic Neurons of the Murine Basal Forebrain
Basal forebrain cholinergic neurons project to the hippocampus and cortex, are critical for learning and memory, and are central to the pathogenesis of Alzheimer's disease (AD). GWAS have consistently shown that genomic variants at the CD2AP gene locus are associated with significant increased risk of AD. GWAS studies have also shown that genetic variants in endocytosis genes, including RAB5A, significantly increase susceptibility to AD. Previous work in our lab has shown that CD2AP functions as a docking-scaffold/adaptor protein as a coordinator of nerve growth factor (NGF) and trophic signaling in neurons. We have also demonstrated that CD2AP positively regulates Rab5-mediated mechanisms of endocytosis in primary sensory neurons. The purpose of this study was to perform an in vivo characterization of CD2AP expression in cholinergic neurons of the brain regions most relevant to AD pathogenesis and to investigate the colocalization of CD2AP and Rab5 in cholinergic neurons of the murine basal forebrain. Brain tissue was perfused, harvested from ChATBAC-eGFP transgenic mice (N=4 male, N=4 female; aged 10 mo), where cholinergic neurons (co-) express green fluorescence protein (GFP) in central and peripheral neurons that express choline acetyltransferase (ChAT). Frozen tissue sections were used to assess the specificity of the reporter in mouse brain along with localization of both CD2AP and Rab5 (co-) expression using immunofluorescence (IF) analysis of ChAT-GFP+ neurons and primary antibodies against ChAT, CD2AP and Rab5. Image J software was used to develop and optimize a colocalization assay for CD2AP and Rab5 puncta. Experiments were repeated in a follow-up cohort of aged-adult mice (N=2 male, N=2 female; aged 18 mo). IF expression of CD2AP was quantified in the basal forebrain, diagonal band of Broca (vDB), and striatal regions and compared to results from the cortical regions of the adult mouse brain. Colocalization of CD2AP was observed in the cell bodies of ChAT-GFP+ neurons of the striatum, vDB and basal forebrain regions, where CD2AP expression intensity as well as the number of cell bodies with positive signal increased incrementally. Colocalization analyses revealed near-complete overlap of CD2AP and Rab5 expression in ChAT-GFP+ cholinergic neurons of the basal forebrain region. We conclude that cholinergic neurons express CD2AP in healthy adult and aged-adult mouse brains. These data provide the first evidence of quantifiable CD2AP protein expression of cholinergic neurons specific to the diagonal band of Broca (vDB) and basal forebrain. Together with previous research from our lab, these data support a role for CD2AP in the pathogenesis of AD through orchestration of endocytosis and retrograde signaling. Ongoing studies are underway to verify these findings in a novel AD mouse model that incorporates the humanized variant of CD2AP, created by MODEL-AD, where we aim to further investigate how CD2AP variants may affect mechanistic components of Rab5 endocytosis as well as subsequent survival of cholinergic neurons in the context of known amyloid beta and Tau pathologies.

Presymptomatic Targeted Circuit Manipulation for Ameliorating Huntington's Disease Pathogenesis
Early stages of Huntington's disease (HD) before the onset of motor and cognitive symptoms are characterized by imbalanced excitatory and inhibitory output from the cortex to striatal and subcortical structures. The window before the onset of symptoms presents an opportunity to adjust the firing rate within microcircuits with the goal of restoring the impaired E/I balance, thereby preventing or slowing down disease progression. Here, we investigated the effect of presymptomatic cell-type specific manipulation of activity of pyramidal neurons and parvalbumin interneurons in the M1 motor cortex on disease progression in the R6/2 HD mouse model. Our results show that dampening excitation of Emx1 pyramidal neurons or increasing activity of parvalbumin interneurons once daily for 3 weeks during the pre-symptomatic phase alleviated HD-related motor coordination dysfunction. Cell-type-specific modulation to normalize the net output of the cortex is a potential therapeutic avenue for HD and other neurodegenerative disorders.

Aberration correction in long GRIN lens-based microendoscopes for extended field-of-view two-photon imaging in deep brain regions
Two-photon (2P) fluorescence imaging through gradient index (GRIN) lens-based endoscopes is fundamental to investigate the functional properties of neural populations in deep brain circuits. However, GRIN lenses have intrinsic optical aberrations, which severely degrade their imaging performance. GRIN aberrations decrease the signal-to-noise ratio (SNR) and spatial resolution of fluorescence signals, especially in lateral portions of the field-of-view (FOV), leading to restricted FOV and smaller number of recorded neurons. This is especially relevant for GRIN lenses of several millimeters in length, which are needed to reach the deeper regions of the rodent brain. We have previously demonstrated a novel method to enlarge the FOV and improve the spatial resolution of two-photon microendoscopes based on GRIN lenses of length < 4.1 mm (Antonini et al. eLife 2020). However, previously developed microendoscopes were too short to reach the most ventral regions of the mouse brain. In this study, we combined optical simulations with fabrication of aspherical polymer microlenses through three-dimensional (3D) microprinting to correct for optical aberrations in long (length > 6 mm) GRIN lens-based microendoscopes (diameter, 500 {micro}m). Long corrected microendoscopes had improved spatial resolution, enabling imaging in significantly enlarged FOVs. Moreover, using synthetic calcium data we showed that aberration correction enabled detection of cells with higher SNR of fluorescent signals and decreased cross-contamination between neurons. Finally, we applied long corrected microendoscopes to perform large-scale and high precision recordings of calcium signals in populations of neurons in the olfactory cortex, a brain region laying approximately 5 mm from the brain surface, of awake head-tethered mice. Long corrected microendoscopes are powerful new tools enabling population imaging with unprecedented large FOV and high spatial resolution in the most ventral regions of the mouse brain.

Satellite glial contact enhances differentiation and maturation of human induced sensory neurons
Induced sensory neurons (iSNs) generated from pluripotent stem cells are used to model human peripheral neuropathies, however current differentiation protocols produce sensory neurons with an embryonic phenotype. Peripheral glial cells contact sensory neurons early in development and contribute to formation of the canonical pseudounipolar morphology, but these signals are not encompassed in current iSN differentiation protocols. Here, we show that terminal differentiation of iSNs in co-culture with rodent Dorsal Root Ganglion satellite glia (rSG) advances their differentiation and maturation. Co-cultured iSNs develop a pseudounipolar morphology through contact with rSGs. This transition depends on semaphorin-plexin guidance cues and on glial gap junction signaling. In addition to morphological changes, iSNs terminally differentiated in co-culture exhibit enhanced spontaneous action potential firing, more mature gene expression, and increased susceptibility to paclitaxel induced axonal degeneration. Thus, iSNs differentiated in coculture with rSGs provide a better model for investigating human peripheral neuropathies.

Motor Cortical Neuronal Hyperexcitability Associated with α-Synuclein Aggregation
Dysfunction of the cerebral cortex is thought to underlie motor and cognitive impairments in Parkinsons disease (PD). While cortical function is known to be suppressed by abnormal basal ganglia output following dopaminergic degeneration, it remains to be determined how the deposition of Lewy pathology disrupts cortical circuit integrity and function. Moreover, it is also unknown whether cortical Lewy pathology and midbrain dopaminergic degeneration interact to disrupt cortical function in late-stage. To begin to address these questions, we injected -synuclein (Syn) preformed fibrils (PFFs) into the dorsolateral striatum of mice to seed Syn pathology in the cortical cortex and induce degeneration of midbrain dopaminergic neurons. Using this model system, we reported that Syn aggregates accumulate in the motor cortex in a layer- and cell-subtype-specific pattern. Particularly, intratelencephalic neurons (ITNs) showed earlier accumulation and greater extent of Syn aggregates relative to corticospinal neurons (CSNs). Moreover, we demonstrated that the intrinsic excitability and inputs resistance of Syn aggregates-bearing ITNs in the secondary motor cortex (M2) are increased, along with a noticeable shrinkage of cell bodies and loss of dendritic spines. Last, neither the intrinsic excitability of CSNs nor their thalamocortical input was altered by a partial striatal dopamine depletion associated with Syn pathology. Our results documented motor cortical neuronal hyperexcitability associated with Syn aggregation and provided a novel mechanistic understanding of cortical circuit dysfunction in PD.

Modeling Nitric Oxide Diffusion and Plasticity Modulation in Cerebellar Learning
Nitric Oxide (NO) is a versatile signalling molecule with significant roles in various physiological processes, including synaptic plasticity and memory formation. In the cerebellum, NO is produced by neural NO Synthase and diffuses to influence synaptic changes, particularly at parallel fiber - Purkinje cell synapses. This study aims to investigate NO's role in cerebellar learning mechanisms using a biologically realistic simulation-based approach. We developed the NO Diffusion Simulator (NODS), a Python module designed to model NO production and diffusion within a cerebellar spiking neural network framework. Our simulations focus on the Eye-Blink Classical Conditioning protocol to assess the impact of NO modulation on long-term potentiation and depression at parallel fiber - Purkinje cell synapses. The results demonstrate that NO diffusion significantly affects synaptic plasticity, dynamically adjusting learning rates based on synaptic activity patterns. This metaplasticity mechanism enhances the cerebellum's capacity to prioritize relevant inputs and mitigate learning interference selectively modulating synaptic efficacy. Our findings align with theoretical models suggesting that NO serves as a contextual indicator, optimizing learning rates for effective motor control and adaptation to new tasks. The NODS implementation provides an efficient tool for large-scale simulations, facilitating future studies on NO dynamics in various brain regions and neurovascular coupling scenarios. By bridging the gap between molecular processes and network-level learning, this work underscores the critical role of NO in cerebellar function and offers a robust framework for exploring NO-dependent plasticity in computational neuroscience.

Cortico-subcortical dynamics in primate working memory
Working memory is essential for cognition, facilitating the temporary maintenance and manipulation of information to produce goal-directed behavior. While both cortical and subcortical structures are involved, their precise roles and interactions are not fully understood. To investigate this, we simultaneously recorded neural activity from the frontal and parietal cortex, higher-order thalamic nuclei, and core basal ganglia structures during color and spatial working memory tasks in non-human primates. We found widespread yet differential encoding of color and spatial information, marked by area-specific temporal dynamics and modulation according to task demands. Both cortical and subcortical information increased towards working memory-dependent actions, suggesting a task-specific reloading of information. Directed interactions between cortical and subcortical regions were extensive and reciprocal, with dominant directions of information flow, especially from frontoparietal areas. These interactions were dynamically modulated and partially task specific. Our findings provide comprehensive insights into the large-scale circuit dynamics underlying primate working memory and suggest that flexible goal-directed behavior relies on the selective processing of task-relevant memory information within information-specific cortico-subcortical networks.

Cerebellar systems consolidation driven by the temporal dynamics of Purkinje cell excitability
Systems consolidation, essential for long-term memory formation, orchestrates the reorganization of newly encoded memories into subsequent neural circuitry. While the role of synaptic mechanism in consolidation is well understood, the contribution of neuronal intrinsic excitability (IE) remains relatively unexplored. Herein, we adopted a cerebellum-dependent learning model, and manipulated IE of the sole output of the cerebellar cortex, Purkinje cells (PCs), to corroborate the direct causality between neuronal IE and memory consolidation and assessed its impact on intrinsic plasticity of the downstream neural circuits. Optogenetic excitation disrupted consolidation but was effective only within the 90 min post-learning time window. Notably, PC-IE temporarily weakened, but the effect faded beyond 90 minutes. Furthermore, abnormally increased PC-IE abolished intrinsic plasticity in flocculus-targeting neurons, a post-circuitry of cortical PCs, within the medial vestibular nucleus. These findings thus emphasize the precise temporal dynamics of IE, highlighting it as a crucial mechanism for systems consolidation.

Melanocortin system activates carotid body arterial chemoreceptors in hypertension
Background: The body's internal milieu is controlled by a system of interoceptors coupled to motor outflows that drive compensatory adaptive responses. These include the arterial chemoreceptors, best known for sensing arterial oxygen. In cardiometabolic diseases, such as essential hypertension, the carotid bodies (CB) exhibit heightened reflex sensitivity and tonic activity without an apparent stimulus. The mechanisms behind CB sensitization in these conditions are not well understood. Methods: Guided by functional genomics, a range of functional assays are used to interrogate downstream intracellular and interorgan signalling pathways involved in arterial chemosensory function. Results: Here, we report the presence of the Melanocortin 4 receptor (MC4R) in the mammalian CB and show its elevated expression in experimental hypertension. We demonstrate that melanocortin agonists activate arterial chemosensory cells, modulating CB chemosensory afferent drive to influence both resting and chemoreflex-evoked sympathetic and ventilatory activity. Transcriptional analysis of hypertensive CB implicates the activation of the Mash1 (Ascl1) regulatory network in driving elevated Mc4r expression. Conclusions: Collectively, our data indicate a primarily pathophysiological role of melanocortin signalling in arterial chemosensation, contributing to excess sympathetic activity in cardiometabolic disease.

Ultrastructural diversity of alpha-Synuclein pathology in the post-mortem brain of Parkinson patients: implications for Lewy Body formation
Lewy bodies, the major pathological hallmark of Parkinson's disease, are intraneuronal inclusions rich in aggregated alpha-synuclein (aSyn). To understand the cellular mechanisms behind the formation of Lewy bodies and the aggregation of aSyn, we used correlative light and electron microscopy and detailed ultrastructural analysis of postmortem brain tissue samples of Parkinson patients. We found that somal aSyn inclusions in dopaminergic neurons were exclusively fibrillar, while membranous-type inclusions were located outside the cell soma and likely compact neuritic aggregates. These neuritic inclusions displayed phenotypic heterogeneity, ranging from predominantly membranous to mixed membranous/fibrillar ultrastructures. Our data suggest that membranous and fibrillar aSyn inclusions form via distinct mechanisms, with membranous neuritic inclusions providing the environment for the initial nucleation of aSyn fibrils, which could then spread via a prion-like mechanism to form somal fibrillar Lewy bodies. This study provides important insight into Lewy body formation and highlights the importance of aSyn and membrane interactions for future therapeutic intervention.

Differential Reactivation of Task-Demand-Associated Firing Patterns in Subicular and CA1 Place Cells during a Hippocampal Memory Task
Reactivation of place cells during sharp-wave ripples (SWRs) in the hippocampus is pivotal for memory consolidation, yet the SWR dynamics between the hippocampus and its neighboring subiculum remain underexplored. This study examined the differential SWR-associated reactivations of task-demand-associated representations in the subiculum and CA1 during a visual scene memory task in rats. In the task, the spiking activities of place-cell ensembles were reactivated during a SWR event according to task demands. These reactivations were more frequent and associated with more heterogeneous task-demand types in the subiculum compared to CA1. These subicular characteristics were driven by multiple subfields within the subicular place field, parcellated by the theta phase precession cycle. In contrast, CA1 exhibited a higher incidence of spatial replay than the subiculum. These findings indicate that the subiculum plays a key role in transmitting task-specific variables from the hippocampus to other brain regions.

Expectation modulates learning emotional words: Evidence from a hierarchical Bayesian model
In language acquisition, individuals learn the emotional value of words through external feedback. Previous studies have used emotional words as experimental materials to explore the cognitive mechanism underlying emotional language processing, but have failed to recognize that languages are acquired in a changing environment. To this end, this study aims to combine reinforcement learning with emotional word learning, using a probabilistic reversal learning task to explore how individuals acquire the valence of emotional words in a dynamically changing environment. Our computational modeling on both behavioral and event-related potential (ERP) data revealed that individuals' expectations can modulate the learning speed and temporal processing of emotional words, demonstrating a clear negative bias. Specifically, as the expected value increases, individuals respond faster and exhibit higher amplitudes for negative emotional words. These findings shed light on the neural mechanisms of emotional word learning in a volatile environment, highlighting the crucial role of expectations in this process and the preference for processing negative information.

Enhancing Statistical Power While Maintaining Small Sample Sizes in Behavioral Neuroscience Experiments Evaluating Success Rates
Studies with low statistical power reduce the probability of detecting true effects and often lead to overestimated effect sizes, undermining the reproducibility of scientific results. While several free statistical software tools are available for calculating statistical power, they often do not account for the specialized aspects of experimental designs in behavioral studies that evaluate success rates. To address this gap, we developed "SuccessRatePower" a free and user-friendly power calculator based on Monte Carlo simulations that takes into account the particular parameters of these experimental designs. Using "SuccessRatePower", we demonstrated that statistical power can be increased by modifying the experimental protocol in three ways: 1) reducing the probability of succeeding by chance (chance level), 2) increasing the number of trials used to calculate subject success rates, and 3) employing statistical analyses suited for discrete values. These adjustments enable even studies with small sample sizes to achieve high statistical power. Finally, we performed an associative behavioral task in mice, confirming the simulated statistical advantages of reducing chance levels and increasing the number of trials in such studies

How to reward animals based on their subjective percepts: A Bayesian approach to online estimation of perceptual biases.
Elucidating the neural basis of perceptual biases, such as those produced by visual illusions, can provide powerful insights into the neural mechanisms of perceptual inference. However, studying the subjective percepts of animals poses a fundamental challenge: unlike human participants, animals cannot be verbally instructed to report what they see, hear, or feel. Instead, they must be trained to perform a task for reward, and researchers must infer from their responses what the animal perceived. However, animals' responses are shaped by reward feedback, thus raising the major concern that the reward regimen may alter the animal's decision strategy or even intrinsic perceptual biases. We developed a method that estimates perceptual bias during task performance and then computes the reward for each trial based on the evolving estimate of the animal's perceptual bias. Our approach makes use of multiple stimulus contexts to dissociate perceptual biases from decision-related biases. Starting with an informative prior, our Bayesian method updates a posterior over the perceptual bias after each trial. The prior can be specified based on data from past sessions, thus reducing the variability of the online estimates and allowing it to converge to a stable estimate over a small number of trials. After validating our method on synthetic data, we apply it to estimate perceptual biases of monkeys in a motion direction discrimination task in which varying background optic flow induces robust perceptual biases. This method overcomes an important challenge to understanding the neural basis of subjective percepts.

Modulation of Neuronal Excitability and Plasticity by BHLHE41 Conveys Lithium Non-Responsiveness
Many bipolar disorder (BD) patients are non-responsive to lithium. The mechanisms underlying lithium (non-)responsiveness are largely unknown. By using gene-set enrichment analysis methods, we found that core clock gene-sets are significantly associated with lithium response. Among the top hits was BHLHE41, a modulator of the molecular clock and homeostatic sleep. Since BHLHE41 and its paralog BHLHE40 are functionally redundant, we assessed chronic lithium response in double-knockout mutant mice (DKO). We demonstrated that DKOs are non-responsive to lithium's effect in various behavioral tasks. Cellular assays and patch clamp recordings revealed lowered excitability and reduced lithium-response in prefrontal cortical layer 2/3 DKO neurons and on hippocampal long-term potentiation. Single-cell RNA sequencing identified that lithium deregulated mitochondrial respiration, cation channel and postsynapse associated gene-sets specifically in upper layer excitatory neurons. Our findings show that lithium acts in a highly cell-specific way on neuronal metabolism and excitability and modulates synaptic plasticity depending on BHLHE40/41.

Non-invasive Ultrasound Deep Neuromodulation of the Human Nucleus Accumbens Increases Win-Stay Behaviour
Precisely neuromodulating deep brain regions in humans could bring transformative advancements in both cognitive neuroscience and brain disorder treatment. In a within subject experiment, twenty-six healthy adults underwent a series of transcranial ultrasound stimulation procedures, including stimulation of the nucleus accumbens, the dorsal anterior cingulate cortex, or no sonication. Results revealed that ultrasound stimulation of the nucleus accumbens (NAcc) induced changes in reward-related behaviours, including in the tendency to stick with winning choices, the rate of learning specifically from positive feedback, and the rate of repeating rewarded choices. Functional brain scans showed corresponding neural changes in response to reward expectations in targeted and interconnected brain areas. These findings demonstrate the causal role of the human NAcc in learning from positive feedback, as well as the feasibility of using non-invasive neuromodulation deep in the human brain to modulate learning and decision making both as a research tool and as a potential component of future treatments for disorders involving reward sensitivity.

Control of tongue movements by the Purkinje cells of the cerebellum
To quantify the cerebellum's contributions to control of the tongue, we trained head-fixed marmosets to make dexterous movements, harvesting food from small tubes that were placed orthogonal to the mouth. We identified the lingual regions in lobule VI of the vermis and recorded from hundreds of Purkinje cells (P-cells), each in sessions where the subject produced thousands of licks. Most movements aimed for one of the small tubes, while other movements groomed the mouth area. To quantify contributions of a P-cell to control of the tongue, we relied on the fact that in a small fraction of the licks, the input from the inferior olive produced a complex spike (CS), which then briefly but completely silenced the P-cell. When the movements were targeting a tube, the CS rates increased during protraction for both ipsilateral and contralateral targets, thus identifying the preferred axis of motion in the olivary input, termed CS-on. However, for grooming movements this modulation was absent. We compared the tongue's trajectory in the targeted movement that had experienced the CS with temporally adjacent targeted licks that had not. When the SS suppression occurred during protraction, the tongue exhibited hypermetria, and when the suppression took place during retraction, the tongue exhibited slowing. These effects amplified when two P-cells were simultaneously suppressed. Therefore, CS-induced suppression of P-cells in the lingual vermis disrupted the forces that would normally decelerate the tongue as it approached the target, demonstrating a specialization in stopping the movement. Because the CS-on direction tended to align with the direction of downstream forces produced during P-cell suppression, this suggests that for targeted licks, the olivary input defined an axis of control for the P-cells.

No evidence of musical training influencing the cortical contribution to the speech-FFR and its modulation through selective attention
Musicians can have better abilities to understand speech in adverse conditions such as background noise than non-musicians. However, the neural mechanisms behind such enhanced behavioral performances remain largely unclear. Studies have found that the subcortical frequency-following response to the fundamental frequency of speech and its higher harmonics (speech-FFR) may be involved since it is larger in people with musical training than in those without. Recent research has shown that the speech-FFR consists of a cortical contribution in addition to the subcortical sources. Both the subcortical and the cortical contribution are modulated by selective attention to one of two competing speakers. However, it is unknown whether the strength of the cortical contribution to the speech-FFR, or its attention modulation, is influenced by musical training. Here we investigate these issues through magnetoencephalographic (MEG) recordings of 52 subjects (18 musicians, 25 non-musicians, and 9 neutral participants) listening to two competing male speakers while selectively attending one of them. The speech-in-noise comprehension abilities of the participants were not assessed. We find that musicians and non-musicians display comparable cortical speech-FFRs and additionally exhibit similar subject-to-subject variability in the response. Furthermore, we also do not observe a difference in the modulation of the neural response through selective attention between musicians and non-musicians. Moreover, when assessing whether the cortical speech-FFRs are influenced by particular aspects of musical training, no significant effects emerged. Taken together, we did not find any effect of musical training on the cortical speech-FFR.

Rescuing behavioral flexibility in a mouse model for OCD by enhancing reward-cue salience
Deficits in cognitive flexibility are a frequent symptom of obsessive-compulsive disorder (OCD) and have been hypothesized to drive compulsive behavior. Sign- and goal-tracking behaviors are thought to be related to cognitive flexibility, yet have not been studied in this context. To investigate the relationship between sign- and goal-tracking behavior and cognitive flexibility, we tested SAPAP3 knockout mice (SAPAP3-/-) and wild-type littermate controls in a Pavlovian reversal-learning task with two conditioned stimuli, one predicting reward delivery and the other reward omission. SAPAP3-/- displayed a heterogenous reversal-learning performance: Half of the population failed to acquire the reversed cue-reward contingencies, whereas the other half reversed their approach behavior similar to control mice. Surprisingly, such behavioral inflexibility and compulsive-like grooming were unrelated, suggesting a non-causal relationship between these traits. Importantly, compromised reversal learning in impaired mice was associated with diminished sign-tracking behavior (and therefore presumably with an overreliance on goal-tracking behavior). Administration of the selective serotonin reuptake inhibitor (SSRI) fluoxetine, the first-line pharmacological OCD treatment, ameliorated both anxiety-like behavior and compulsive-like grooming, but did not improve behavioral flexibility in SAPAP3-/. In contrast, enhancing reward-cue salience by altering conditioned stimuli brightness improved behavioral flexibility through augmenting sign-tracking behavior. These findings suggest that deficits in behavioral flexibility are associated with imbalanced sign- and goal-tracking behaviors in SAPAP3-/-, and enhancing reward-cue salience can rescue behavioral flexibility by restoring the balance. Thus, sign- and goal-tracking behavior might be an underexplored cognitive mechanism that could potentially be exploited to improve cognitive flexibility in OCD patients.