bioRxiv Subject Collection: Neuroscience's Journal

Sex-specific effects of early life unpredictability on hippocampal and amygdala responses to novelty in adolescents
Background: Unpredictable childhood experiences are an understudied form of early life adversity that impacts neurodevelopment in a sex-specific manner. The neurobiological processes by which exposure to early-life unpredictability impacts development and vulnerability to psychopathology remain poorly understood. The present study investigates the sex-specific consequences of early-life unpredictability on the limbic network, focusing on the hippocampus and the amygdala. Methods: Participants included 150 youth (54% female). Early life unpredictability was assessed using the Questionnaire of Unpredictability in Childhood (QUIC). Participants engaged in a task-fMRI scan between the ages of 8 and 17 (223 total observations) measuring BOLD responses to novel and familiar scenes. Results: Exposure to early-life unpredictability associated with BOLD contrast (novel vs. familiar) in a sex-specific manner. For males, but not females, higher QUIC scores were associated with lower BOLD activation in response to novel vs. familiar stimuli in the hippocampal head and amygdala. Secondary psychophysiological interaction (PPI) analyses revealed complementary sex-specific associations between QUIC and condition-specific functional connectivity between the right and left amygdala, as well as between the right amygdala and hippocampus bilaterally. Conclusion: Exposure to unpredictability in early life has persistent implications for the functional operations of limbic circuits. Importantly, consistent with emerging experimental animal and human studies, the consequences of early life unpredictability differ for males and females. Further, impacts of early-life unpredictability were independent of other risk factors including lower household income and negative life events, indicating distinct consequences of early-life unpredictability over and above more commonly studied types of early life adversity.

PointTree: Automatic and accurate reconstruction of long-range axonal projections of single-neuron
Single-neuron axonal projections reveal the route map of neuron output and provide a key cue for understanding how information flows across the brain. Reconstruction of single-neuron axonal projections requires intensive manual operations in tens of terabytes of brain imaging data, and is highly time-consuming and labor-intensive. The main issue lies in the need for precise reconstruction algorithms to avoid reconstruction errors, yet current methods struggle with densely distributed axons, focusing mainly on skeleton extraction. To overcome this, we introduce a point assignment-based method that uses cylindrical point sets to accurately represent axons and a minimal information flow tree model to suppress the snowball effect of reconstruction errors. Our method successfully reconstructs single-neuron axonal projections across hundreds of GBs images with an average of 80% F1-score, while current methods only provide less than 40% F1-score reconstructions from a few hundred MBs images. This huge improvement is helpful for high-throughput mapping of neuron projections.

Bridging the gap between the connectome and whole-brain activity in C. elegans
A fundamental goal of neuroscience is to understand how anatomy determines the functional properties of the nervous system. However, it has been challenging to relate large-scale functional measurements of the C. elegans nervous system to the worm's known anatomical connectome1-3. Here, we address this apparent discrepancy using a connectome-constrained model of the nematode brain fit to neural recordings with optogenetic perturbations2. Our model consists of a noisy linear dynamical system with a sparse synaptic weight matrix with non-zero entries only where there are synapses in the C. elegans connectome. We evaluated the model by perturbing neurons in silico and measuring the perturbation response of all other neurons in the network. We compared these responses to those measured in held-out animals and found that this model captured the perturbation-triggered responses of individual neurons 92% as well as the reproducibility of the perturbation responses themselves. This includes perturbation responses of neurons that were not anatomically connected, which the model explains in terms of signal propagation over multiple neurons. In addition to capturing perturbation responses, the model also accurately predicts the activity of held-out neurons using the observed activity of other neurons. Strikingly, alternative models with equivalent levels of sparsity but a shuffled connectome constraint achieved much lower performance. Finally, we demonstrate that adding connections beyond those found in the connectome did not improve the model's prediction of the perturbation measurements. The model described here provides the strongest link yet between the connectivity of the C. elegans nervous system and its causal and correlative functional properties.

Constructing a Mouse Brain Atlas of Dendritic Microenvironments Helps Discover Hidden Associations Between Anatomical Layout, Projection Targets and Transcriptomic Profiles of Neurons
Digital brain atlases have become essential anatomical references for understanding the spatial and functional organization of brains. For mice, typical resources include the Allen Reference Atlas, the Allen Common Coordinate Framework (CCF), and their variants, like CCFv3. However, previous whole-brain atlases were constructed based on limited neuronal features, such as cell body (soma) density or average maps from collections of registered brain images, without considering the spatial organization of neuronal arbors. This study introduces a microenvironment representation that incorporates the morphological features of neighboring neurons to better quantify brain modularity. We generated a large dataset containing dendrites from 101,136 neurons across 111 mouse brains, covering 91% of non-ventricular, non-fiber-tract CCF regions, and constructed a multidimensional microenvironment feature map of the whole brain. Our findings reveal that the spatial organization of these microenvironments outperforms the CCFv3 and a state-of-the-art spatial transcriptomic cell atlas by providing complementary subregions within established regions, nearly doubling the total number of brain regions compared to CCFv3. In this way, our atlas enables the identification of previously unobserved neuron groupings or "subtypes". Our results also demonstrate that this microenvironment atlas enhances local spatial homogeneity while maintaining spatial differentiation within established CCF brain regions. For example, we found that the microenvironments of hippocampal neurons are correlated with axonal projection targets and improve the specificity of projection mapping, which implies the potential characterization of long-range axonal projections of mammalian neurons based on only local dendritic organization. The sub-parcellation of the caudoputamen (CP) aligns well with previous studies on projections, connectivity, and transcriptomics, revealing diverse input and output wiring patterns among CP subregions.

Tau P301S Transgenic Mice Develop Gait and Eye Movement Impairments That Mimic Progressive Supranuclear Palsy
Progressive supranuclear palsy (PSP) is a neurodegenerative disorder with an estimated prevalence of 5-7 people in 100,000. Clinically characterized by impairments in gait, balance, and eye movements, as well as aggregated Tau pathology, PSP leads to death in approximately 5-8 years. No disease-modifying treatments are currently available. The contribution of Tau pathology to the symptoms of patients with PSP is poorly understood, in part due to lack of a rodent model that recapitulates characteristic aspects of PSP. Here, we assessed the hTau.P301S mouse for key clinical features of PSP, finding progressive impairments in balance and gait coordination. Additionally, we found impairments in fast vertical eye movements, one of the most distinctive features of PSP. Across animals, we found that Tau pathology in motor control regions correlated with motor deficits. These findings highlight the utility of the hP301S mouse in modeling key aspects of PSP.

Examination of low-intensity focused ultrasound parameters for human neuromodulation
Background: Low-intensity focused ultrasound (LIFU) is a promising form of non-invasive neuromodulation characterized by a rich parameter space that includes intensity, duration, duty cycle and pulsing strategy. The effect and interaction of these parameters to affect human brain activity is poorly understood. A better understanding of how parameters interact is critical to advance LIFU as a potential therapeutic. Objective/Hypothesis: To determine how different parameters, including intensity, duration, and duty cycle interact to produce neuromodulation effects in the human brain. Further, this study assesses the effect of pulsing versus continuous ultrasound. We hypothesize that higher duty cycles will confer excitation. Increasing intensity or duration will increase the magnitude of effect. Pulsing LIFU will not be more effective than continuous wave ultrasound. Methods: N = 18 healthy human volunteers underwent 20 different parameter combinations that included a fully parametrized set of two intensities (ISPPA: 6 & 24 W/cm2), five duty cycles (1, 10, 30, 50, 70%) and two durations (100, 500 msec) with a constant pulse repetition frequency of 1 kHz delivered concurrently with transcranial magnetic stimulation (TMS) to the primary motor cortex (M1). Four of these parameter combinations were also delivered continuously, matched on the number of cycles. Motor-evoked potential (MEP) amplitude was the primary outcome measure. All parameter combinations were collected time-locked to MEP generation. Results: There was no evidence of excitation from any parameter combination. 3 of the 24 parameter sets resulted in inhibition. The parameter set that resulted in the greatest inhibition (~ 30%) was an intensity of 6W/cm2 with a duty cycle of 30% and a duration of 500 msec. A three-way ANOVA revealed an interaction of intensity and duty cycle. The analysis of continuous versus pulsed ultrasound revealed a 3-way interaction of intensity, pulsing, and the number of cycles such that under the 6W/cm2 condition higher cycles of pulsed ultrasound resulted in inhibition whereas lower number of cycles using continuous LIFU resulted in inhibition. Conclusions: LIFU to M1 in humans, in the range employed, either conferred inhibition or had no effect. Significant excitation was not observed. In general, lower intensity looks to be more efficacious for inhibition that depends on duration. Finally, pulsed ultrasound looks to be more effective for inhibition as compared to continuous wave after controlling for total energy delivered.

Premorbid Characteristics of the SAPAP3-Mouse Model of Obsessive-Compulsive Disorder: Behavior, Neuroplasticity, and Psilocybin Treatment
Deletion of the SAPAP3 gene in mice results in a characteristic phenotype that manifests from the age of 4-6 months and consists of repetitive bouts of self-grooming, head-body twitches, and anxiety-related behaviors. The phenotype is attenuated by sub-chronic fluoxetine and by single injections of ketamine and psilocybin and is considered a model for OCD. We investigated the premorbid characteristics of SAPAP3 knockout (SAPAP3-KO) mice. Two cohorts of juvenile SAPAP3-KO mice (aged 10-13 weeks) were assessed for anxiety and other behavioral phenotypes. Compared to wild-type (WT) mice, male and female homozygous SAPAP3-KO mice manifested significant anxiety-like behaviors in the open field and elevated plus maze tests, reduced marble burying, and altered performance on the buried Oreo test. These behaviors were not alleviated by psilocybin treatment. Adult male SAPAP3-KO mice showed increased levels of synaptic proteins (GAP43, synaptophysin, and SV2A) in the frontal cortex, hippocampus, and amygdala, while adult female SAPAP3-KO mice showed increased SV2A in the frontal cortex. These findings suggest enhanced synaptic growth and vesicle-associated plasticity in adult SAPAP3-KO mice that may reflect a compensatory mechanism. Increased synaptic proteins were not observed in juvenile mice, suggesting age-dependent alterations in neuroplasticity. Our finding that SAPAP3-KO mice exhibit anxiety-like behaviors before the onset of compulsive grooming is analogous to prodromal anxiety observed in patients with OCD. The study provides a basis for further research into the development of OCD-like behaviors and associated neuroplasticity changes and for studying potential treatments.

The Visual Experience Evaluation Tool: A Myopia Research Instrument for Quantifying Visual Experience
Current myopia research has demonstrated the role of extended visual experience in healthy ocular development. Optical cues and the spectrum, intensity, and temporal characteristics of light landing on the retina are all known factors affecting the development of the eye. However, there is still limited understanding as to which of these extrinsic factors are most important or how they interplay with intrinsic physical and neural differences between individuals. Part of the problem is inadequate tooling. Our team at Reality Labs Research created the Visual Environment Evaluation Tool (VEET), a non-commercial research instrument, to accelerate myopia research. In this paper, we describe the VEET's physical design, sensor suite and capabilities, and the associated software which makes it well-suited for research of quantified visual experience.

TWINKLE: An open-source two-photon microscope for teaching and research
Many laboratories use two-photon microscopy through commercial suppliers, or homemade designs of considerable complexity. The integrated nature of these systems complicates customization, troubleshooting as well as grasping the principles of two-photon microscopy. Here, we present "Twinkle": a microscope for Two-photon Imaging in Neuroscience, and Kit for Learning and Education. It is a fully open, high-performance and cost-effective research and teaching microscope without any custom parts beyond what can be fabricated in a university machine shop. The instrument features a large field of view, using a modern objective with a long working distance and large back aperture to maximize the fluorescence signal. We document our experiences using this system as a teaching tool in several two week long workshops, exemplify scientific use cases, and conclude with a broader note on the place of our work in the growing space of open-source scientific instrumentation.

Mouse PAW: reverse-translating the FINGER multimodal lifestyle intervention enhances synaptic plasticity and cognition in adult wild type female mice
Background: Targeting multiple risk factors through preventive interventions can halt the onset or progression of dementia. The clinical efficacy of this approach was shown in the multimodal FINGER trial, yet knowledge of the underlying biological mechanisms is limited. In the current study, we applied for the first time a multimodal lifestyle intervention in mice to study effects on cognition and associated molecular pathways. Methods: We have established a novel experimental model, the lifestyle intervention PAW (Prevention of Alzheimer's by a Multimodal Lifestyle Protocol - Working-mechanisms for Memory Gains) in mice. In this model, we combined different modalities of intervention aiming to achieve synergistic effects. The animals were given access to running wheels (voluntary exercise), Fortasyn Connect (a medical food that slows disease progression in early Alzheimer's disease), and they were subjected to cognitive training in an IntelliCage environment (PAW group). To separately investigate the effects of pharmacological vascular management as a preventive measure, another group of mice was given Atorvastatin and Enalapril (cholesterol and blood pressure lowering pharmaceuticals, respectively) dosed in the diet (Pharma group). Control mice were housed in normal conditions. We included 12 wild type C57BL/6J female mice 6.5 months of age per group. The full intervention lasted for 8 weeks. Blood pressure was measured at baseline and the end of the intervention. All mice underwent a battery of behavioural testing after the eight weeks of intervention. Hippocampi were dissected for proteomics analysis. Results: During the intervention, the PAW group actively participated in the intervention by learning the different cognitive training programs and by using the running wheels. At the end of the intervention, the PAW group showed a lowering of blood pressure to a similar extent as in the Pharma group (systolic 158 mmHg to 139 mmHg, p = 0.003, and 163 mmHg to 136 mmHg, p = 0.042, respectively). Furthermore, the PAW group displayed a better short-term spatial working memory compared to the control group as assessed by the spontaneous alternation in the Y maze test (66.5% and 56.7%, respectively, p = 0.036). Proteomic analysis of the hippocampi and downstream bioinformatic analysis revealed that several pathways were upregulated in the PAW mice including synaptogenesis (Z = 4.27, p = 1.26E-18) and glutamate binding, activation of AMPA receptors and synaptic plasticity (Z = 3.74, p = 3.16E-19). Conclusions: Our findings suggest that the PAW model effectively mimics the clinical effects of multimodal lifestyle dementia prevention, and further demonstrates the activation of hippocampal-specific molecular drivers of memory gains.

Natural variations of adult neurogenesis and anxiety predict hierarchical status of inbred mice
Hierarchy provides a survival advantage to social animals in challenging circumstances. In mice, social dominance is associated with trait anxiety and reduced stress resilience which are regulated by adult hippocampal neurogenesis. Here, we tested whether adult hippocampal neurogenesis may regulate social dominance behavior. We observed that future dominant individuals exhibited higher trait anxiety and lower levels of hippocampal neurogenesis prior to social hierarchy formation, suggesting that baseline neurogenesis might predict individual social status among a group. This phenotype persisted after social hierarchy was stable. Experimentally reducing neurogenesis prior to the stabilization of social hierarchy in group-housed males increased the probability of mice to become dominant and increased anxiety. Finally, when innate dominance was assessed in socially isolated and anxiety-matched animals, mice with impaired neurogenesis displayed a dominant status toward strangers. Together, these results indicate that adult neurogenesis predicts and regulates hierarchical and situational dominance behavior along with anxiety-related behavior. These results provide a framework to study the mechanisms underlying social hierarchy and the dysregulation of dominance behavior in psychiatric diseases related to anxiety.

PHluorin-conjugated secondary nanobodies as a tool for measuring synaptic vesicle exo- and endocytosis
Neuronal communication relies on synaptic vesicle recycling, which has long been investigated by live imaging approaches. Synapto-pHluorins, genetically encoded reporters that incorporate a pH-sensitive variant of GFP within the lumen of the synaptic vesicle, have been especially popular. However, they require genetic manipulation, implying that a tool combining their excellent reporter properties with the ease of use of classical immunolabeling would be desirable. We introduce this tool here, relying on primary antibodies against the luminal domain of synaptotagmin 1, decorated with secondary single-domain antibodies (nanobodies) carrying a pHluorin moiety. The application of the antibodies and nanobodies to cultured neurons results in labeling their recycling vesicles, without the need for any additional manipulations. The labeled vesicles respond to stimulation, in the expected fashion, and the pHluorin signals enable the quantification of both exo- and endocytosis. We conclude that pHluorin-conjugated secondary nanobodies are a convenient tool for the analysis of vesicle recycling.

Effects of sensorimotor delays and muscle force capacity limits on the performance of feedforward and feedback control in animals of different sizes
Animals rely on both feedforward and feedback control for perturbation responses. When comparing animals of different sizes, we find that several features that affect perturbation responses change - larger animals have longer sensorimotor time delays, heavier body segments and proportionally weaker muscles. We used simple computational models to compare fast perturbation response times under feedforward and feedback control, as a function of animal size. We developed two tasks representing common perturbation response scenarios in animal locomotion: a distributed mass pendulum approximating swing limb repositioning (swing task), and an inverted pendulum approximating whole body posture recovery (posture task). First, we used a normalized feedback control system to show how feedback response times can either be limited by the force generation capacity of muscles (force-limited), or by sensorimotor delays which constrain the maximum feedback gains that can be used to produce stable responses (delay-limited). Next, we used more detailed scaled models which represent the full-size range of terrestrial mammals and parameterized the sensorimotor delays, maximum muscle forces, and inertial properties using published scaling relationships from literature. Across animal size and in both tasks, we found that feedback control was primarily delay-limited - the fastest responses used a fraction of the available muscle force capacity. Feedforward control, which is able to fully activate muscles and produce faster responses - was about four times faster than feedback control in the smallest animals, and around two times faster in the largest animals. For rapid perturbation responses, feedback control appears ineffective for terrestrial mammals of all sizes, as the fastest response times exceeded available movement times, while feedforward control did not. Thus, feedforward control is more effective for reacting quickly to sudden and large perturbations in animals of all sizes.

Congruent brain signatures specific to speech sounds in fronto-temporal cortex during language production and understanding.
In this fMRI study we investigated whether language production and understanding recruit the same phoneme-specific networks. We did so by comparing the brain response to different phoneme categories in minimal pairs: Bilabial-initial words (e.g., monkey) were contrasted to alveolar-initial words (e.g., donkey) in 37 participants performing both language production and perception tasks. Region-of-Interest analyses showed that the same sensori-motor networks were activated across the language modalities. In motor regions, word production and comprehension elicited the same phoneme-specific topographical activity patterns, with stronger haemodynamic activations for alveolar-initial words in the tongue cortex and stronger activations for bilabial-initial words in the lip cortex. In the posterior and middle superior temporal cortex, production and comprehension likewise resulted in similar activity patterns, with enhanced activations to alveolar- compared to bilabial-initial words. These results disagree with the classical separation between speech production and understanding in neurobiological models of language, and instead advocate for a cortical organization where the same phoneme-specific acoustic-and-articulatory representations carry language production and understanding.

Olfactory and Trigeminal Routes of HSV-1 CNS Infection with Regional Microglial Heterogeneity
Herpes simplex virus type 1 (HSV-1) primarily targets the oral and nasal epithelia before establishing latency in the trigeminal and other peripheral ganglia (TG). HSV-1 can also infect and go latent in the central nervous system (CNS) independent of latency in the TGs. Recent studies suggest entry to the CNS via two distinct routes: the TG-brainstem connection and olfactory nerve; however, to date, there is no characterization of brain regions targeted during HSV-1 primary infection. Furthermore, the immune response by microglia may also contribute to the heterogeneity between different brain regions. However, the response to HSV-1 by microglia has not been characterized in a region-specific manner. This study investigated the time course of HSV-1 spread within the olfactory epithelium (OE) and CNS following intranasal inoculation and the corresponding macrophage/microglial response in a C57BL/6 mouse model. We found an apical to basal spread of HSV-1 within the OE and underlying tissue accompanied by an inflammatory response of macrophages. OE Infection was followed by infection of a small subset of brain regions targeted by the TG in the brainstem, as well as other cranial nerve nuclei, including the vagus and hypoglossal nerve. Furthermore, other brain regions were positive for HSV-1 antigens, such as the locus coeruleus (LC), raphe nucleus (RaN), and hypothalamus, while sparing the hippocampus and cortex. Within each brain region, microglia activation also varied widely. These findings provide critical insights into the region-specific dissemination of HSV-1 within the CNS, elucidating potential mechanisms linking viral infection to neurological and neurodegenerative diseases.

Whole-brain dynamics and hormonal shifts throughout women's lifespan: From reproductive stages to menopausal transition and beyond
Neuroimaging studies have identified significant age-related disruptions in whole-brain dynamics, yet the influence of women's reproductive stages and associated hormonal shifts remains underexplored. This study leverages resting-state fMRI data from the Human Connectome Project in Aging to examine brain dynamics through five reproductive stages: reproductive, late reproductive, perimenopause, early postmenopause, and late postmenopause. Our results indicate that the late reproductive stage is characterized by the highest dynamical complexity across whole-brain and resting-state networks, while brain dynamics significantly decline at menopause onset. Additionally, we employ machine learning classifiers using two approaches: (1) brain dynamics alone and (2) brain dynamics combined with follicle-stimulating hormone (FSH) and estradiol (brain-hormone model). Both models accurately distinguished reproductive stages, but the brain-hormone model outperformed the brain dynamics model. Key predictors included decreased estradiol, increased FSH, and altered brain dynamics in later life stages. These results offer a framework for assessing brain health across women's reproductive lifespan.

Distinct Neural Representations of Hunger and Thirst in Neonatal Mice before the Emergence of Food- and Water-seeking Behaviors
Hunger and thirst are two fundamental drives for maintaining homeostasis, and elicit distinct food- and water-seeking behaviors essential for survival. For neonatal mammals, however, both hunger and thirst are sated by consuming milk from their mother. While distinct neural circuits underlying hunger and thirst drives in the adult brain have been characterized, it is unclear when these distinctions emerge in neonates and what processes may affect their development. Here we show that hypothalamic hunger and thirst regions already exhibit specific responses to starvation and dehydration well before a neonatal mouse can seek food and water separately. At this early age, hunger drives feeding behaviors more than does thirst. Within neonatal regions that respond to both hunger and thirst, subpopulations of neurons respond distinctly to one or the other need. Combining food and water into a liquid diet throughout the animal's life does not alter the distinct representations of hunger and thirst in the adult brain. Thus, neural representations of hunger and thirst become distinct before food- and water-seeking behaviors mature and are robust to environmental changes in food and water sources.

Traumatic Brain Injury Exacerbates Alcohol Consumption and Neuroinflammation with Decline in Cognition and Cholinergic Activity
Traumatic brain injury (TBI) is a global health challenge, responsible for 30% of injury-related deaths and significantly contributing to disability. Annually, over 50 million TBIs occur worldwide, with most adult patients at emergency departments showing alcohol in their system. TBI is also a known risk factor for alcohol abuse, yet its interaction with alcohol consumption remains poorly understood. In this study, we demonstrate that the fluid percussion injury (FPI) model of TBI in mice significantly increases alcohol consumption and impairs cognitive function. At cellular levels, FPI markedly reduced the number and activity of striatal cholinergic interneurons (CINs) while increasing microglial cells. Notably, depleting microglial cells provided neuroprotection, mitigating cholinergic loss and enhancing cholinergic activity. These findings suggest that TBI may promote alcohol consumption and impair cognitive abilities through microglia activation and consequently reduced cholinergic function. Our research provides critical insights into the mechanisms linking TBI with increased alcohol use and cognitive deficits, potentially guiding future therapeutic strategies.

Musicianship modulates cortical (but not brainstem) effects of attention on processing musical triads
Background: Many studies have demonstrated benefits of long-term music training (i.e., musicianship) on the neural processing of sound, including simple tones and speech. However, the effects of musicianship on the encoding of simultaneously presented pitches, in the form of complex musical chords, is less well-established. Presumably, musicians' stronger familiarity and active experience with tonal music might enhance harmonic pitch representations, perhaps in an attention-dependent manner. Additionally, attention might influence chordal encoding differently across the auditory system. To this end, we explored the effects of long-term music training and attention on processing of musical chords at brainstem and cortical levels. Method: Young adult participants were separated into musician and nonmusician groups based on extent of formal music training. While recording EEG, listeners heard isolated musical triads that differed only in the chordal third: major, minor, and detuned (4% sharper third from major). Participants were asked to correctly identify chords via key press during active stimulus blocks and watched a silent movie during passive blocks. We logged behavioral identification accuracy and reaction times and calculated information transfer based on the behavioral chord confusion patterns. EEG data were analyzed separately to distinguish between cortical (event-related potential, ERP) and subcortical (frequency-following response, FFR) evoked responses. Results: We found musicians were (expectedly) more accurate, though not faster, than nonmusicians in chordal identification. For subcortical FFRs, responses showed stimulus chord effects but no group differences. However, for cortical ERPs, whereas musicians displayed P2 (~150 ms) responses that were invariant to attention, nonmusicians displayed earlier and reduced P2 during passive listening. Listeners' degree of behavioral information transfer (i.e., success in distinguishing chords) was also better in musicians and correlated with their neural differentiation of chords, assessed via pairwise differences in the ERPs. Conclusions: Our data suggest long-term music training strengthens even the passive cortical processing of musical sounds, supporting more automated brain processing of musical chords with less reliance on attention. Our results also suggest the degree to which listeners can behaviorally distinguish chordal triads is directly related to their neural specificity to musical sounds primarily at cortical rather than subcortical levels.

Neural geometry efficiently representing abstract form of value and modality in the primate basal ganglia
Basal ganglia process diverse values from various modalities using limited resources, necessitating efficient processing. This involves converging tactile and visual information within bimodal value-coding neurons, ensuring efficient processing with limited number of neurons. However, convergence at the single neuron level may compromise modality-specific information, raising the question: Does efficient processing inevitably degrade information quality? We investigated the representational geometry in the putamen of macaque monkeys trained to learn values from tactile and visual inputs. Here, we demonstrated that the population representation of bimodal value-coding neurons in the putamen preserved both value and modality information, and these representations were shared to efficiently maintain quality. Notably, these representations were generalized across identical modalities and values, resulting in an efficient low-dimensional representation. Furthermore, a faster transformation to a generalized value representation within neural geometry reflected greater confidence in value-guided choice behavior-this correlation not observed in conventional decoding. Our results suggest that bimodal value-coding neurons play a key role in balancing efficiency and information fidelity, facilitating cognitive states required for confident decision-making.

Widespread brain activity increases in frontal lobe seizures with impaired consciousness
Impaired consciousness is a serious clinical manifestation of epilepsy with negative consequences on quality of life. Little work has investigated impaired consciousness in frontal lobe seizures, a common form of focal epilepsy. In temporal lobe seizures, previous studies showed widespread cortical slow waves associated with depressed subcortical arousal and impaired consciousness. However, in frontal lobe epilepsy, it is not known whether cortical slow waves are present, or whether a very different cortical activity pattern may be related to impaired consciousness. We used intracranial EEG recordings of 65 frontal lobe seizures in 30 patients for quantitative analysis of ictal cortical activity and its relationship to impaired consciousness. Behavioral changes based on blinded review of seizure videos were used to classify focal aware, focal impaired awareness, and focal to bilateral tonic-clonic seizures. Changes in intracranial EEG power from preictal baseline were analyzed in different cortical regions and across frequency ranges in these three categories. We found that frontal lobe focal aware seizures showed approximately 40% increases in intracranial EEG power localized to the frontal lobe of seizure onset across frequency ranges, with relatively smaller changes in other cortical regions. Frontal lobe focal impaired awareness seizures showed approximately 50% increases in intracranial EEG power, not significantly different from focal aware seizures in the frontal lobe of seizure onset (P = 1.038), but significantly greater than focal aware seizures in other broad cortical regions (P < 0.001). Importantly, the widespread cortical increases in EEG power observed in focal impaired awareness versus focal aware seizures were seen not just in the frequency range of slow waves, but were also observed across other frequencies including fast activity. However, the widespread cortical increases in focal impaired awareness seizures differed from focal to bilateral tonic-clonic seizures where intracranial EEG power increased to a much higher level by approximately 600%. The large power increases in focal to bilateral tonic-clonic were significantly greater than in focal impaired awareness seizures both in the frontal lobe of seizure onset and in other cortical regions (P < 0.001). Our findings contrast with focal temporal lobe epilepsy, where impaired consciousness is associated with cortical slow waves. We can speculate that different focal seizure types produce impaired consciousness by impacting widespread cortical regions but through different physiological mechanisms. Insights gained by studying mechanisms of impaired consciousness may be the first step towards developing novel treatments to prevent this important negative consequence of epilepsy.

Rational inattention in neural coding for economic choice
Mental operations like computing the value of an option are computationally expensive. Even before we evaluate options, we must decide how much attentional effort to invest in the evaluation process. More precise evaluation will improve choice accuracy, and thus reward yield, but the gain may not justify the cost. Rational Inattention theories provide an accounting of the internal economics of attentionally effortful economic decisions. To understand this process, we examined choices and neural activity in several brain regions in six macaques making risky choices. We extended the rational inattention framework to incorporate the foraging theoretic understanding of local environmental richness or reward rate, which we predict will promote attentional effort. Consistent with this idea, we found local reward rate positively predicted choice accuracy. Supporting the hypothesis that this effect reflects variations in attentional effort, richer contexts were associated with increased baseline and evoked pupil size. Neural populations likewise showed systematic baseline coding of reward rate context. During increased reward rate contexts, ventral striatum and orbitofrontal cortex showed both an increase in value decodability and a rotation in the population geometries for value. This confluence of these results suggests a mechanism of attentional effort that operates by controlling gain through using partially distinct population codes for value. Additionally, increased reward rate accelerated value code dynamics, which have been linked to improved signal-to-noise. These results extend the theory of rational inattention to static and stationary contexts and align theories of rational inattention with specific costly, neural processes.

The ER stress transcription factor Luman/CREB3 is a novel regulator of Schwann cell survival and myelinating capacity through the activation of the unfolded protein response and cholesterol biosynthesis pathways
Misfolded protein accumulation in demyelinating disorders or injury can trigger internal endoplasmic reticulum (ER) stress alleviation mechanisms, namely the unfolded protein response (UPR) and cholesterol biosynthesis pathways. Here we demonstrate that the ER stress-associated transcription factor Luman/CREB3, herein called Luman, shown to drive axon regeneration by UPR-dependent regulation of adaptive low-level stress, also positively regulates rat Schwann cell (SC) survival, myelination, the UPR, and cholesterol production in vitro. siRNA knockdown of SC Luman expression decreased SC viability and increased apoptosis 48 hours post-transfection. Dorsal root ganglion (DRG) neuron/SC co-cultures where SCs overexpressed Luman exhibited increased myelination. Simulation of unstressed, mild and moderate ER stress by tunicamycin mediated UPR induction in SCs, allowed examination of Luman on expression of known UPR regulators, including Xbp1, Xbp1s, CHOP, and pIRE1. They collectively demonstrate a cytoprotective role for Luman under manageable ER stress. Total cholesterol levels and sterol precursor Srebf1 expression, key to myelination, also decreased following Luman knockdown. Finally, levels of mature brain-derived neurotrophic factor (mBDNF), a positive regulator of myelination and also regulated by the UPR, decreased with Luman knockdown. In contrast, proapoptotic BDNF precursor (proBDNF) levels increased in Luman-deficient SCs at higher ER stress levels, indicating that any protection Luman confers at moderate ER stress levels is lost upon its reduced expression. In conclusion, a connection between Luman and adaptive beneficial ER stress pathways linked to survival and myelination capacity in SCs exists. These Luman-driven cytoprotective mechanisms including survival and myelination open avenues for targeting this pathway in nerve trauma and myelinating disorders.

Cholinergic Neuronal Activity Promotes Diffuse Midline Glioma Growth through Muscarinic Signaling
Neuronal activity promotes the proliferation of healthy oligodendrocyte precursor cells (OPC) and their malignant counterparts, gliomas. Many gliomas arise from and closely resemble oligodendroglial lineage precursors, including diffuse midline glioma (DMG), a cancer affecting midline structures such as the thalamus, brainstem and spinal cord. In DMG, glutamatergic and GABAergic neuronal activity promotes progression through both paracrine signaling and through bona-fide neuron-to-glioma synapses. However, the putative roles of other neuronal subpopulations - especially neuromodulatory neurons located in the brainstem that project to long-range target sites in midline anatomical locations where DMGs arise - remain largely unexplored. Here, we demonstrate that the activity of cholinergic midbrain neurons modulates both healthy OPC and malignant DMG proliferation in a circuit-specific manner at sites of long-range cholinergic projections. Optogenetic stimulation of the cholinergic pedunculopontine nucleus (PPN) promotes glioma growth in pons, while stimulation of the laterodorsal tegmentum nucleus (LDT) facilitates proliferation in thalamus, consistent with the predominant projection patterns of each cholinergic midbrain nucleus. Reciprocal signaling was evident, as increased activity of cholinergic neurons in the PPN and LDT was observed in pontine DMG-bearing mice. In co-culture, hiPSC-derived cholinergic neurons form neuron-to-glioma networks with DMG cells and robustly promote proliferation. Single-cell RNA sequencing analyses revealed prominent expression of the muscarinic receptor genes CHRM1 and CHRM3 in primary patient DMG samples, particularly enriched in the OPC-like tumor subpopulation. Acetylcholine, the neurotransmitter cholinergic neurons release, exerts a direct effect on DMG tumor cells, promoting increased proliferation and invasion through muscarinic receptors. Pharmacological blockade of M1 and M3 acetylcholine receptors abolished the activity-regulated increase in DMG proliferation in cholinergic neuron-glioma co-culture and in vivo. Taken together, these findings demonstrate that midbrain cholinergic neuron long-range projections to midline structures promote activity-dependent DMG growth through M1 and M3 cholinergic receptors, mirroring a parallel proliferative effect on healthy OPCs.

Systematic changes in neural selectivity reflect the acquired salience of category-diagnostic dimensions
Humans and other animals develop remarkable behavioral specializations for identifying, differentiating, and acting on classes of ecologically important signals. Ultimately, this expertise is flexible enough to support diverse perceptual judgments: a voice, for example, simultaneously conveys what a talker says as well as myriad cues about her identity and state. Mature perception across complex signals thus involves both discovering and learning regularities that best inform diverse perceptual judgments, and weighting this information flexibly as task demands change. Here, we test whether this flexibility may involve endogenous attentional gain to task-relevant dimensions. We use two prospective auditory category learning tasks to relate a complex, entirely novel soundscape to four classes of ''alien identity'' and two classes of ''alien size. '' Identity, but not size, categorization requires discovery and learning of patterned acoustic input situated in one of two simultaneous, frequency-delimited bands. This allows us to capitalize on the coarsely segregated frequency-band-specific channels of auditory tonotopic maps using fMRI to ask whether category-relevant perceptual information is prioritized relative to simultaneous, uninformative information. Among participants expert at alien identity categorization, we observe prioritization of the diagnostic frequency band that persists even when the diagnostic information becomes irrelevant in the size categorization task. Tellingly, the neural selectivity evoked implicitly in categorization aligns closely with activation driven by explicit, sustained selective attention to other sounds presented in the same frequency band. Additionally, we observe fingerprints of individual differences in the learning trajectories taken to achieve expert-level categorization in patterns of neural activity associated with the diagnostic dimension. In all, this indicates that acquiring categories can drive the emergence of acquired attentional salience to dimensions of acoustic input.

Postnatal Enrichment Corrects Deficits in Perineuronal Net Formation and Reversal Learning in Adult Mice Exposed to Early Adversity
Childhood neglect is associated with cortical thinning, hyperactivity, and deficits in cognitive flexibility that are difficult to reverse later in life. Despite being the most prevalent form of early adversity, little is currently understood about the mechanisms responsible for these neurodevelopmental abnormalities, and no animal models have yet replicated key structural and behavioral features of childhood neglect/deprivation. To address these gaps, we have recently demonstrated that mice exposed to impoverished conditions, specifically limited bedding (LB), exhibit behavioral and structural changes that resemble those observed in adolescents who have experienced severe neglect. Here, we show that LB leads to long-term deficits in reversal learning, which can be fully reversed by briefly exposing LB pups to enrichment (toys) in their home cage from postnatal days 14 to 25. Reversal learning failed to induce normal c-fos activation in the orbitofrontal cortex (OFC) of LB mice, a deficit that was normalized by early enrichment. Additionally, LB decreased the density of parvalbumin-positive cells surrounded by perineuronal nets (PV+PNN+) and increased the ratio of glutamatergic to inhibitory synapse densities in the OFC, deficits that were also reversed by enrichment. Degradation of PNN in the OFC of adult mice impaired reversal learning, reduced c-fos activation, and increased the ratio of glutamatergic to inhibitory synapse densities in the OFC to levels comparable to those observed in LB mice. Collectively, our findings suggest that postnatal deprivation and enrichment impact the formation of PV+PNN+ cells in the OFC, a developmental process that is essential for cognitive flexibility in adulthood.

Inferring Effective Networks of Spiking Neurons Using a Continuous-Time Estimator of Transfer Entropy
When analysing high-dimensional time-series datasets, the inference of effective networks has proven to be a valuable modelling technique. This technique produces networks where each target node is associated with a set of source nodes that are capable of providing explanatory power for its dynamics. Multivariate Transfer Entropy (TE) has proven to be a popular and effective tool for inferring these networks. Recently, a continuous-time estimator of TE for event-based data such as spike trains has been developed which, in more efficiently representing event data in terms of inter-event intervals, is significantly more capable of measuring multivariate interactions. The new estimator thus presents an opportunity to more effectively use TE for the inference of effective networks from spike trains, and we demonstrate in this paper for the first time its efficacy at this task. Using data generated from models of spiking neurons - for which the ground-truth connectivity is known - we demonstrate the accuracy of this approach in various dynamical regimes. We further show that it exhibits far superior inference performance to a pairwise TE-based approach as well as a recently-proposed convolutional neural network approach. Moreover, comparison with Generalised Linear Models (GLMs), which are commonly applied to spike-train data, showed clear benefits, particularly in cases of high synchrony. Finally, we demonstrate its utility in revealing the patterns by which effective connections develop from recordings of developing neural cell cultures.