bioRxiv Subject Collection: Neuroscience's Journal

Evidence of sensory error threshold in triggering locomotor adaptations in humans
Changing body biomechanics or external conditions trigger neural adaptations to optimize motor behavior. While the adaptations appear continuous to minimize movement errors, not all errors necessarily initiate sensorimotor adaptations. The locomotor system exhibits resilience to change and rehabilitation. This suggests the presence of an error threshold to trigger the adaptation mechanism. Here, we imposed kinematic and kinetic constraints of stepping using a passive orthosis and real-time feedback about limb loading. We aimed to manipulate stepping asymmetry and explore the interplay between adaptation and locomotor error magnitude. Uninjured healthy adults were tested in three locomotor conditions: unconstrained, constrained, and washout unconstrained walking. Surprisingly, kinematic asymmetry alone did not induce persistent adaptation. However, the addition of asymmetric interlimb loading triggered the expected adaptation. Our finding suggests that uninjured locomotor systems can cope with a specific range of kinematic asymmetries without initiating persistent adaptations that lead to aftereffects, and that loading may be a key variable for evoking the adaptation. The presence of an error threshold may mitigate possible disruption of vital motor functions and contribute to locomotor adaptation during walking. These insights elucidate the mechanism of neural plasticity and have implications for rehabilitation.

Multiparameter Quantitative Analyses of Diagnostic Cells in Brain Tissues from Tuberous Sclerosis Complex
The advent of high-dimensional imaging approaches offers innovative opportunities to molecularly characterize diagnostic cells in disorders that have previously relied on histopathological definitions. One example of such disorders is tuberous sclerosis complex (TSC), a developmental disorder characterized by systemic growth of benign tumors. Within resected brain tissues from patients with TSC, detection of abnormally enlarged balloon cells (BCs) is pathognomonic for this disorder. Though BCs can be identified by an expert neuropathologist, little is known about the specificity and broad applicability of protein markers for these cells, complicating classification of proposed BCs identified in experimental models of this disorder. Here, we report the development of a customized machine-learning workflow (Balloon Identifier; BAIDEN) that was trained to prospectively identify BCs in tissue sections using a histological stain compatible with high-dimensional cytometry. This approach was coupled to a custom antibody panel and 36-parameter imaging mass cytometry (IMC) to explore the expression of multiple previously proposed BC markers and develop a descriptor of BC features conserved across multiple tissue samples from patients with TSC. These findings comprise a toolbox and dataset for understanding the abundance, structure, and signaling activity of these histopathologically abnormal cells, and an example case of how such tools can be developed and applied within human tissues.

A Telescopic Independent Component Analysis on Functional Magnetic Resonance Imaging Data Set
Brain function can be modeled as the dynamic interactions between functional sources at different spatial scales, and each spatial scale can contain its functional sources with unique information, thus using a single scale may provide an incomplete view of brain function. This paper introduces a novel approach, termed "Telescopic independent component analysis (ICA)," designed to construct spatial functional hierarchies and estimate functional sources across multiple spatial scales using fMRI data. The method employs a recursive ICA strategy, leveraging information from a larger network to guide the extraction of information about smaller networks. We apply our model to study the default mode network (DMN) and evaluate the difference between healthy people and individuals with schizophrenia. We show that the telescopic ICA approach can detect the spatial hierarchy of DMN and their associated group differences between cohorts that may not be captured if we focus on a single-scale ICA. In sum, our proposed approach represents a promising new tool for studying functional sources.

Voice patches in the marmoset auditory cortex revealed by wide-field calcium imaging
Species-specific vocalizations are behaviorally critical sounds. Similar to faces, species-specific vocalizations are important for the survival and social interactions of both humans and vocal animals. Face patches have been found in the brains of both human and non-human primates. In humans, a voice patch system has been identified on the lateral superior temporal gurus (STG) that is selective to human voices over other sounds. In non-human primates, while vocalization-selective regions were found on the rostral portion of the temporal lobe outside of the auditory cortex in both macaques and marmosets using functional magnetic resonance imaging (fMRI), it is yet clear whether vocalization-selective regions are present in the auditory cortex. Using wide-field calcium imaging, a technique with both high temporal and high spatial resolution, we discovered two voice patches in the marmoset auditory cortex that preferentially respond to marmoset vocalizations over other sounds and carry call types and identity information. One patch is located on the posterior primary auditory cortex (A1), and the other one is located on the anterior non-core region of the auditory cortex. These voice patches are functionally connected and hierarchically organized as shown by latency and selectivity analyses. Our findings reveal the existence of voice patches in the auditory cortex of marmosets and support the notion that similar cortical architectures are adapted for recognizing communication signals for both vocalizations and faces in different primate species.

A Systematically Optimized Miniaturized Mesoscope (SOMM) for large-scale calcium imaging in freely moving mice
Understanding how neuronal dynamics gives rise to ethologically relevant behavior requires recording of neuronal population activity via technologies that are compatible with unconstrained animal behavior. However, realizations of cellular resolution head-mounted microscopes for mice have been based on conventional microscope designs that feature various forms of ad-hoc miniaturization and weight reduction measures necessary for compatibility with the weight-limits for free animal behavior. As a result, they have typically remained limited to a small field of view (FOV) or low resolution, a shallow depth range and often remain susceptible to motion-induced artifacts. Here, we present a systematically optimized miniaturized mesoscope (SOMM), a widefield, head-mounted fluorescent mesoscope based on a principled optimization approach that allows for mesoscale, cellular resolution imaging of neuroactivity while offering robustness against motion-induced artifacts. This is achieved by co-optimization of a compact diffractive optical element and the associated computational algorithm under form-factor and weight constraints while maximizing the obtainable FOV, depth of field (DOF), and resolution. SOMM enables recordings of neuronal population activity at up to 16 Hz within a FOV of 3.6 x 3.6 mm^2 in the cortex of freely moving mice while featuring 4-{micro}m resolution, a DOF of 300 {micro}m at a weight of less than 2.5 g. We show SOMM's performance of recording large-scale neuronal population activity during social interactions, during conditioning-type experiments and by investigating neurovascular coupling using dual-color imaging.

Causal Discovery Analysis Reveals Insights into Psychosis Proneness, Brain Function, and Environmental Factors among Young Individuals
Background: Experiencing symptoms of psychosis, such as delusions and hallucinations, are observed in general, nonclinical populations. These experiences are sometimes described as psychosis proneness (PP) and potentially part of the psychosis continuum. The directional relationships among various factors contributing to psychosis proneness and its interactions, encompassing both environmental and neural mechanisms, lack comprehensive description. We aimed to identify targets to prevent psychosis proneness and its interactions by characterizing pathways using causal discovery analysis (CDA). Methods: Participants were 194 healthy adolescent and young adult twin and sibling pairs aged between 14-24 years from Turkiye. They completed comprehensive assessments evaluating sociodemographic status, environmental risk, general intelligence, self-schema, PP, and working memory (WM) performance during fMRI (37 variables). CDA was applied, a novel machine learning algorithm, to understand the causal relationships of PP. Results: The analysis identified negative self-schema as having the largest causal effect among all assessments in PP [Effect size (ES)= 0.55]. Secondly, social cohesion and trust (SC&T) had a protective causal effect on PP [ES= -0.18]. Lastly, PP was identified as a direct cause of greater activation in DLPFC (BA9a-BA46v) during manipulation in the WM (ES= 0.14). Conclusions: CDA provides directionality of the 37 variables which were not presented earlier. The findings highlight the significance of negative self-schema and SC&T in the general population with PP, emphasizing the potential for preventive interventions targeting these factors. These findings also suggest a role for DLPFC as a potential target in this regard. To our knowledge, this is the first study using data-driven analysis to model causal mechanisms in PP in the general population.

A Neural Mechanism for Optic Flow Parsing in Macaque Visual Cortex
For the brain to compute object motion in the world during self-motion, it must discount the global patterns of image motion (optic flow) caused by self-motion. Optic flow parsing is a proposed visual mechanism for computing object motion in the world, and studies in both humans and monkeys have demonstrated perceptual biases consistent with the operation of a flow parsing mechanism. However, the neural basis of flow parsing remains unknown. We demonstrate, at both the individual unit and population levels, that neural activity in macaque area MT is biased by peripheral optic flow in a manner that can at least partially account for perceptual biases induced by flow parsing. These effects cannot be explained by conventional surround suppression mechanisms or choice-related activity, and have a substantial neural latency. Together, our findings establish the first neural basis for the computation of scene-relative object motion based on flow parsing.

London taxi drivers exploit neighbourhood boundaries for hierarchical route planning
Humans show an impressive ability to plan over complex situations and environments. A classic approach to explaining such planning has been tree-search algorithms which search through alternative state sequences for the most efficient path through states. However, this approach fails when the number of states is large due to the time to compute all possible sequences. Hierarchical route planning has been proposed as an alternative, offering a computationally efficient mechanism in which the representation of the environment is segregated into clusters. Current evidence for hierarchical planning comes from experimentally created environments which have clearly defined boundaries and far fewer states than the real-world. To test for real-world hierarchical planning we exploited the capacity of London licensed taxi drivers to use their memory to construct a street by street plan across London, UK (>26,000 streets). The time to recall each successive street name was treated as the response time, with a rapid average of 1.8 seconds between each street. In support of hierarchical planning we find that the clustered structure of London's regions impacts the response times, with minimal impact of the distance across the street network (as would be predicted by tree-search). We also find that changing direction during the plan (e.g. turning left or right) is associated with delayed response times. Thus, our results provide real-world evidence for how humans structure planning over a very large number of states, and give a measure of human expertise in planning.

Autonomic modulations to cardiac dynamics in response to affective touch: Differences between social touch and self-touch
The autonomic nervous system plays a vital role in self-regulation and responding to environmental demands. Autonomic dynamics have been hypothesized to be involved in perceptual awareness and the physiological implementation of the first-person perspective. Based on this idea, we hypothesized that the autonomic activity measured from cardiac dynamics could differentiate between social touch and self-touch. In our study, we used a newly developed method to analyze the temporal dynamics of cardiac sympathetic and parasympathetic activities during an ecologically valid affective touch experiment. We revealed that different types of touch conditions-social-touch, self-touch, and a control object-touch-resulted in a decrease in sympathetic activity. This decrease was more pronounced during social touch, as compared to the other conditions. Following sympathetic decrease, we quantified an increase in parasympathetic activity specifically during social touch, further distinguishing it from self-touch. Importantly, by combining the sympathetic and parasympathetic indices, we successfully differentiated social touch from the other experimental conditions, indicating that social touch exhibited the most substantial changes in cardiac autonomic indices. These findings may have important clinical implications as they provide insights into the neurophysiology of touch, relevant for aberrant affective touch processing in specific psychiatric disorders and for the comprehension of nociceptive touch.

Maternal Immune Activation Alters Temporal Precision of Spike Generation of CA1 Pyramidal Neurons by Unbalancing GABAergic Inhibition in the Offspring
Maternal immune activation (MIA) represents a risk factor for neuropsychiatric disorders associated with neurodevelopmental alterations. A growing body of evidence from rodents and non-human primates shows that MIA induced by viral or bacterial infections results in several neurobiological alterations in the offspring. These changes may play an important role in the pathophysiology of psychiatric disorders like schizophrenia and autism spectrum disorders, whose clinical features include impairments in cognitive processing and social performance. Such alterations are causally associated with the maternal inflammatory response to infection rather than with the infection itself. Previously, we reported that CA1 pyramidal neurons of mice exposed to MIA exhibit increased excitability accompanied by a reduction in dendritic complexity. However, potential alterations in cellular and synaptic rules that shape the neuronal computational properties of the offspring remain to be determined. In this study, using mice as subjects, we identified a series of cellular and synaptic alterations endured by CA1 pyramidal neurons of the dorsal hippocampus in a lipopolysaccharideinduced MIA model. Our data provide evidence that MIA reshapes the excitationinhibition balance by decreasing the perisomatic GABAergic inhibition impinging on CA1 pyramidal neurons. These alterations yield a dysregulated amplification of the temporal and spatial synaptic integration. In addition, MIA-exposed offspring displayed social and anxiety-like abnormalities. Collectively, these findings contribute to the understanding of the cellular and synaptic alterations underlying the behavioral symptoms present in neurodevelopmental disorders associated with MIA.

Microglia are not required for maintenance of blood-brain barrier properties in health, but PLX5622 alters brain endothelial cholesterol metabolism
Microglia are resident immune cells of the central nervous system, yet their functions far exceed those related to immunology. From pruning neural synapses during development to preventing excessive neural activity throughout life, microglia are intimately involved in the brain's most basic processes. Studies have reported a close interaction between microglia and endothelial cells, as well as both helpful and harmful roles for microglia at the blood-brain barrier (BBB) in the context of disease. However, much less work has been done to understand microglia-endothelial cell interactions in the healthy brain. Here, we aim to determine the role of microglia at the healthy BBB. We used the colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 to deplete microglia and analyzed BBB ultrastructure, permeability, and transcriptome. Interestingly, we found that, despite their direct contact with endothelial cells, microglia are not necessary for maintenance of BBB structure, function, or gene expression in the healthy brain. However, we found that PLX5622 treatment alters brain endothelial cholesterol metabolism, and this effect was independent from microglial depletion, suggesting PLX5622 has off-target effects on brain vasculature.

Asiatic acid improves mitochondrial function, activates antioxidant response in the mouse brain and improves cognitive function in beta-amyloid overexpressing mice.
Extracts of the plant Centella asiatica can enhance mitochondrial function, promote antioxidant activity and improve cognitive deficits. Asiatic acid (AA) is one of the constituent triterpene compounds present in the plant. In this study we explore the effects of increasing concentrations of AA on brain mitochondrial function, antioxidant response and cognition in healthy mice and a single concentration of AA in the beta-amyloid overexpressing 5xFAD mouse line. Associative memory and overall activity were assessed. Hippocampal mitochondrial bioenergetics and the expression of mitochondrial and antioxidant response genes was determined. In the 5xFAD line, total beta-amyloid plaque burden after AA treatment was also evaluated. In healthy mice, we report dose responsive effects of increasing concentrations of AA on enhanced associative memory and a dose dependent increase in basal and maximal mitochondrial respiration, mitochondrial gene expression and antioxidant gene expression. Results from the highest AA dose (1% AA) were similar to what was observed with CAW. The high AA dose was then evaluated in the context of A{beta} accumulation in 5xFAD mice. Improvements in mitochondrial and antioxidant response genes were favored in females over males without significant alleviation of A{beta} plaque burden.

Graspable foods and tools elicit similar responses in visual cortex
Extrastriatal visual cortex is known to exhibit distinct response profiles to complex stimuli of varying ecological importance (e.g., faces, scenes, and tools). The dominant interpretation of these effects is that they reflect activation of distinct `category-selective' brain regions specialized to represent these and other stimulus categories. We sought to explore an alternative perspective: that the response to these stimuli is determined less by whether they form distinct categories, and more by their relevance to different forms of natural behavior. In this regard, food is an interesting test case, since it is primarily distinguished from other objects by its edibility, not its appearance, and there is evidence of food-selectivity in human visual cortex. Food is also associated with a common behavior, eating, and food consumption typically also involves the manipulation of food, often with the hands. In this context, food items share many properties in common with tools: they are graspable objects that we manipulate in self-directed and stereotyped forms of action. Thus, food items may be preferentially represented in extrastriatal visual cortex in part because of these shared affordance properties, rather than because they reflect a wholly distinct kind of category. We conducted fMRI and behavioral experiments to test this hypothesis. We found that behaviorally graspable food items and tools were judged to be similar in their action-related properties, and that the location, magnitude, and patterns of neural responses for images of graspable food items were similar in profile to the responses for tool stimuli. Our findings suggest that food-selectivity may reflect the behavioral affordances of food items rather than a distinct form of category-selectivity.

Local desensitization to dopamine devalues recurring behavior
Goal achievement adjusts the relative importance of future behaviors. We use Drosophila to study this form of motivational control, finding that prior matings make males increasingly likely to abandon future copulations when challenged. Repetition-induced devaluation results from a reduction in dopamine reception by the Copulation Decision Neurons (CDNs), which mediate the decision to end matings. Dopamine signaling to the CDNs sustains matings in real time, but also triggers a lasting, {beta}-arrestin-dependent desensitization of the D2R on the CDNs, leaving subsequent matings susceptible to disruption. When D2R desensitization is experimentally prevented, the male treats each mating as if it were his first. These findings provide a generalizable mechanism of motivational control and reveal a natural function for the long-studied susceptibility of the D2R to drug-induced inactivation.

Recurrent neural networks as neuro-computational models of human speech recognition
Human speech recognition transforms a continuous acoustic signal into categorical linguistic units, by aggregating information that is distributed in time. It has been suggested that this kind of information processing may be understood through the computations of a Recurrent Neural Network (RNN) that receives input frame by frame, linearly in time, but builds an incremental representation of this input through a continually evolving internal state. While RNNs can simulate several key behavioral observations about human speech and language processing, it is unknown whether RNNs also develop computational dynamics that resemble human neural speech processing. Here we show that the internal dynamics of long short-term memory (LSTM) RNNs, trained to recognize speech from auditory spectrograms, predict human neural population responses to the same stimuli, beyond predictions from auditory features. Variations in the RNN architecture motivated by cognitive principles further improve this predictive power. Moreover, different components of hierarchical RNNs predict separable components of brain responses to speech in an anatomically structured manner, suggesting that RNNs reproduce a hierarchy of speech recognition in the brain. Our results suggest that RNNs provide plausible computational models of the cortical processes supporting human speech recognition.

Development of radial frequency pattern perception in macaque monkeys
Infant primates see poorly, and most perceptual functions mature steadily beyond early infancy. Behavioral studies on human and macaque infants show that global form perception, as measured by the ability to integrate contour information into a coherent percept, improves dramatically throughout the first several years after birth. However, it is unknown when sensitivity to curvature and shape emerges in early life. We studied the development of shape sensitivity in eighteen macaques, aged 2 months to 10 years. Using radial frequency stimuli (RFS), circular targets whose radii are modulated sinusoidally, we tested monkeys ability to discriminate RFS from circles as a function of the depth and frequency of sinusoidal modulation. We implemented a new 4-choice oddity task and compared the resulting data with that from a traditional 2-alternative task. Behavioral performance at all radial frequencies improved with age. Performance was better for higher radial frequencies, suggesting the developing visual system prioritizes processing of fine visual details that are ecologically relevant. By utilizing two complementary methods, we were able to capture a comprehensive developmental trajectory for shape perception.

Transcription factor-mediated generation of dopaminergic neurons from human iPSCs: a comparison of methods
Dopaminergic neurons are the predominant brain cells affected in Parkinson's disease. With the limited availability of live human brain dopaminergic neurons to study pathological mechanisms of Parkinson's disease, dopaminergic neurons have been generated from human skin cell-derived induced pluripotent stem cells. Originally, induced pluripotent stem cell-derived dopaminergic neurons were generated using small molecules. These neurons took more than two months to mature. However, transcription factor-mediated differentiation of induced pluripotent stem cells has revealed quicker and cheaper methods to generate dopaminergic neurons. In this study, we compare and contrast three protocols to generate induced pluripotent stem cell-derived dopaminergic neurons using transcription factor-mediated directed differentiation. We deviated from the established protocols using lentivirus transduction to stably integrate transcription factors into induced pluripotent stem cells, followed by differentiation using different media compositions. We introduced three transcription factors into the AAVS1 safe harbour locus of induced pluripotent stem cells, and in combination with small molecules, we generated more than 80% neurons in the culture, out of which more than 80% neurons were dopaminergic neurons. Therefore, a combination of transcription factors along with small molecule treatment may be required to generate a pure population of human dopaminergic neurons, a prerequisite for cell replacement therapies.

Differential functions of the dorsal and intermediate regions of the hippocampus for optimal goal-directed navigation in VR space
Goal-directed navigation requires the hippocampus to process spatial information in a value-dependent manner, but its underlying mechanism needs to be better understood. Here, we investigated whether the dorsal (dHP) and intermediate (iHP) regions of the hippocampus differentially function in processing place and its associated value information. Rats were trained in a place-preference task involving reward zones with different values in a visually rich VR environment where two-dimensional navigation was possible. Rats learned to use distal visual scenes effectively to navigate to the reward zone associated with a higher reward. Inactivation of the dHP or iHP with muscimol altered navigational patterns differentially. Specifically, measurements of the efficiency and accuracy of wayfinding behavior using directional analysis showed that iHP inactivation induced more severe damage to value-dependent navigation than dHP inactivation. Our findings suggest that the dHP is more critical for accurate spatial navigation to the target location per se, whereas the iHP is critical for finding higher-value goal locations.

Dynamic representation of appetitive and aversive stimuli in nucleus accumbens shell D1- and D2-medium spiny neurons
The nucleus accumbens (NAc) is a key brain region for motivated behaviors, yet how distinct neuronal populations encode appetitive or aversive stimuli remains undetermined. Using microendoscopic calcium imaging, we tracked NAc shell D1- or D2-medium spiny neurons (MSNs) activity during exposure to stimuli of opposing valence and associative learning. Despite drift in individual neurons coding, both D1- and D2-population activity was sufficient to discriminate opposing valence unconditioned stimuli, but not predictive cues. Notably, D1- and D2-MSNs were similarly co-recruited during appetitive and aversive conditioning, supporting a concurrent role in associative learning. Conversely, when contingencies changed, there was an asymmetric response in the NAc, with more pronounced changes in the activity of D2-MSNs. Optogenetic manipulation of D2-MSNs provided causal evidence of the necessity of this population in the extinction of aversive associations. Our results reveal how NAc shell neurons encode valence, Pavlovian associations and their extinction, and unveil new mechanisms underlying motivated behaviors.

Molecular and Cellular Mechanisms of Teneurin Signaling in Synaptic Partner Matching
In developing brains, axons exhibit remarkable precision in selecting synaptic partners among many non- partner cells. Evolutionally conserved teneurins were the first identified transmembrane proteins that instruct synaptic partner matching. However, how intracellular signaling pathways execute teneurin's functions is unclear. Here, we use in situ proximity labeling to obtain the intracellular interactome of teneurin (Ten-m) in the Drosophila brain. Genetic interaction studies using quantitative partner matching assays in both olfactory receptor neurons (ORNs) and projection neurons (PNs) reveal a common pathway: Ten-m binds to and negatively regulates a RhoGAP, thus activating the Rac1 small GTPases to promote synaptic partner matching. Developmental analyses with single-axon resolution identify the cellular mechanism of synaptic partner matching: Ten-m signaling promotes local F-actin levels and stabilizes ORN axon branches that contact partner PN dendrites. Combining spatial proteomics and high-resolution phenotypic analyses, this study advanced our understanding of both cellular and molecular mechanisms of synaptic partner matching.

High or Low Expectations: Expected intensity of action outcome is embedded in action ‎kinetics
Goal-directed actions are performed in order to attain certain sensory consequences in the world. However, expected attributes of these consequences can affect the kinetics of the action. In a set of three studies (n=120), we examined how expected attributes of stimulus outcome (intensity) shape the kinetics of the triggering action (applied force), even when the action and attribute are independent. We show that during action execution (button presses), the expected intensity of sensory outcome implicitly affects the applied force of the stimulus-producing action in an inverse fashion. Thus, participants applied more force when the expected intensity of the outcome was low (vs. high intensity outcome). In the absence of expectations or when actions were performed in response to the sensory event, no intensity-dependent force modulations were found. Thus, causality and expectations of stimulus intensity play an important role in shaping action kinetics. Finally, we examined the relationship between kinetics and perception and found no influence of applied force level on perceptual detection of low intensity (near-threshold) outcome stimuli, suggesting no causal link between the two. Taken together, our results demonstrate that action kinetics are implicitly embedded with high-level context such as the expectation of consequence intensity and the causal relationship with environmental cues.

Estradiol elicits distinct firing patterns in arcuate nucleus kisspeptin neurons of females through altering ion channel conductances
Hypothalamic kisspeptin (Kiss1) neurons are vital for pubertal development and reproduction. Arcuate nucleus Kiss1 (Kiss1ARH) neurons are responsible for the pulsatile release of Gonadotropin-releasing Hormone (GnRH). In females, the behavior of Kiss1ARH neurons, expressing Kiss1, Neurokinin B (NKB), and Dynorphin (Dyn), varies throughout the ovarian cycle. Studies indicate that 17beta-estradiol (E2) reduces peptide expression but increases Vglut2 mRNA and glutamate neurotransmission in these neurons, suggesting a shift from peptidergic to glutamatergic signaling. To investigate this shift, we combined transcriptomics, electrophysiology, and mathematical modeling. Our results demonstrate that E2 treatment upregulates the mRNA expression of voltage-activated calcium channels, elevating the whole-cell calcium current and contributing to high-frequency firing. Additionally, E2 treatment decreased the mRNA levels of Canonical Transient Receptor Potential (TPRC) 5 and G protein-coupled K+ (GIRK) channels. When TRPC5 channels in Kiss1ARH neurons were deleted using CRISPR, the slow excitatory postsynaptic potential (sEPSP) was eliminated. Mathematical modeling confirmed the importance of TRPC5 channels for initiating and sustaining synchronous firing, while GIRK channels, activated by Dyn binding to kappa opioid receptors, were responsible for repolarization. Our findings suggest that E2 modifies ionic conductance in Kiss1ARH neurons, enabling the transition from high frequency synchronous firing through NKB-driven activation of TRPC5 channels to a short bursting mode facilitating glutamate release. In a low E2 milieu, synchronous firing of Kiss1ARH neurons drives pulsatile release of GnRH, while the transition to burst firing with high, preovulatory levels of E2 facilitates the GnRH surge through its glutamatergic synaptic connection to preoptic Kiss1 neurons.

Local Delivery of Soluble Fractalkine (CX3CL1) Peptide Restore Ribbon Synapses After Noise-Induced Cochlear Synaptopathy
Efficacy of chemokine fractalkine isoforms was evaluated for restoration of loss of inner hair cell ribbon synapses and hearing after noise-induced cochlear synaptopathy (NICS). Previously, we have demonstrated a critical role for fractalkine signaling axis (CX3CL1-CX3CR1) in synaptic repair where in the presence of fractalkine receptor (CX3CR1) expressed by cochlear macrophages, the damaged synapses are spontaneously repaired. Here, we examined whether overexpression of fractalkine ligand (CX3CL1 or FKN) in the form of a peptide is effective in restoring the lost synapses and hearing after NICS. Remarkably, single transtympanic (TT) injection of soluble isoform of FKN (sFKN) peptide at 1 day after synaptopathic noise trauma showed significant recovery of ABR thresholds, ABR peak I amplitudes and ribbon synapses in both FKN-wildtype and knockout mice when compared to mice injected with full length membrane-bound FKN peptide (mFKN). Mechanistically, sFKN peptide treatment increased macrophage numbers in the cochlea and in the absence of those macrophages, sFKN failed to restore loss of synapses and hearing after NICS. Furthermore, sFKN treatment attenuated cochlear inflammation after noise overexposure without altering the expression of CX3CR1. Finally, sFKN peptide was detectable inside the cochlea localized to the sensory epithelium for 24 hours after TT injection. These data provide a robust proof-of-principle that local delivery of an immune factor, sFKN is effective in restoring lost ribbon synapses and hearing after NICS in a macrophage-dependent manner and highlights the potential of sFKN as an immunotherapy for cochlear synaptopathy due to noise or aging.

Effects of head-only exposure to 900 MHz GSM electromagnetic fields in rats : changes in neuronal activity as revealed by c-Fos imaging without concomitant cognitive impairments
Over the last decade, animal models have been used to evaluate the physiological and cognitive effects of mobile phone exposures. Here, we used a head-only exposure system in rats to determine whether exposure to 900MHz GSM electromagnetic fields (EMF) induces regional changes in neuronal activation as revealed by c-Fos imaging. In a first study, rats were exposed for 2h to brain average specific absorption rates (BASARs) ranging from 0.5 to 6W/kg. Changes in neuronal activation were found to be dose-dependent with significant increases in c-Fos expression occurring at BASAR of 1W/kg in prelimbic, infralimbic, frontal and cingulate cortices. In a second study, animals were submitted to either a spatial working memory (WM) task in a radial maze or a spatial reference memory (RM) task in an open field arena. Exposures (45min) were conducted before each training session (BASARs of 1 and 3.5W/kg). Control groups included sham-exposed and control cage animals. In both tasks, behavioral performance evolved similarly in the four groups over testing days. However, c-Fos staining was significantly reduced in cortical areas (prelimbic, infralimbic, frontal, cingulate and visual cortices) and in hippocampus of animals engaged in the WM task (BASARs of 1 and 3.5W/kg). In the RM task, EMF exposure-induced decreases were limited to temporal and visual cortices (BASAR of 1W/kg). These results demonstrate that both acute and subchronic exposures to 900MHz EMFs can produce biological effects, but these effects were not sufficient to induce detectable cognitive deficits in the tasks used here.

Psychological stress disturbs bone metabolism via miR-335-3p/Fos signaling in osteoclast
It has been well-validated that chronic psychological stress leads to bone loss, but the underlying mechanism remains unclarified. In this study, we established and analyzed the chronic unpredictable mild stress (CUMS) mice to investigate the miRNA-related pathogenic mechanism involved in psychological stress-induced osteoporosis. Our result found that these CUMS mice exhibited osteoporosis phenotype that mainly attributed to the abnormal activities of osteoclasts. Subsequently, miRNA sequencing and other analysis showed that miR-335-3p, which is normally highly expressed in the brain, was significantly down-regulated in the nucleus ambiguous (NAC), serum, and bone of the CUMS mice. Additionally, in vitro studies detected that miR-335-3p is important for osteoclast differentiation, with its direct targeting site in Fos. Further studies demonstrated Fos was upregulated in CUMS osteoclast, and the inhibition of Fos suppressed the accelerated osteoclastic differentiation, as well as the expression of osteoclastic genes, such as Nfatc1, Acp5, Mmp9, in miR-335-3p restrained osteoclasts. In conclusion, this work indicated that psychological stress may down-regulate the miR-335-3p expression, which resulted in the accumulation of Fos and the up-regulation of NFACT1 signaling pathway in osteoclasts, leading to its accelerated differentiation and abnormal activity. These results decipher a previously unrecognized paradigm that miRNA can act as a link between psychological stress and bone metabolism.

Liver-innervating vagal sensory neurons play an indispensable role in the development of hepatic steatosis in mice fed a high-fat diet.
The visceral organ-brain axis, mediated by vagal sensory neurons in the vagal nerve ganglion, is essential for maintaining various physiological functions. These vagal sensory neurons relay interoceptive signals from visceral organs to the medulla. In this study, we investigate the influence of the loss of the liver-brain axis on energy balance, glucose homeostasis, and hepatic steatosis in mice under obesogenic conditions. A subset of vagal sensory neurons innervating the liver is located in both the left and right ganglia, projecting centrally to the nucleus of the tractus solitarius, area postrema, and dorsal motor nucleus of the vagus, and peripherally to the periportal areas in the liver. Ablation of the liver-brain axis via caspase-induced selective destruction of advillin-positive neurons prevents diet-induced obesity in male and female mice, and these outcomes are associated with increased energy expenditure. Although males and females exhibit improved glucose homeostasis following disruption of the liver-brain axis, only male mice display increased insulin sensitivity. Furthermore, loss of the liver-brain axis limits the progression of hepatic steatosis in male and female mice fed a steatogenic diet. Therefore, modulation of the liver-brain axis may present a therapeutic strategy for restoring lipid metabolism and glucose homeostasis in obesity and diabetes.

A doubly stochastic renewal framework for partitioning spiking variability
The firing rate is a prevalent concept used to describe neural computations, but estimating dynamically changing firing rates from irregular spikes is challenging. An inhomogeneous Poisson process, the standard model for partitioning firing rate and spiking irregularity, cannot account for diverse spike statistics observed across neurons. We introduce a doubly stochastic renewal point process, a flexible mathematical framework for partitioning spiking variability, which captures the broad spectrum of spiking irregularity from periodic to super-Poisson. We validate our partitioning framework using intracellular voltage recordings and develop a method for estimating spiking irregularity from data. We find that the spiking irregularity of cortical neurons decreases from sensory to association areas and is nearly constant for each neuron under many conditions but can also change across task epochs. A spiking network model shows that spiking irregularity depends on connectivity and can change with external input. These results help improve the precision of estimating firing rates on single trials and constrain mechanistic models of neural circuits.

Neural decoding of the speech envelope: Effects of intelligibility and spectral degradation
During continuous speech perception, patterns of endogenous neural activity become time-locked to acoustic stimulus features, such as the speech amplitude envelope. This speech-brain coupling can be decoded using non-invasive brain imaging techniques, including electroencephalography (EEG). Methods like these may provide clinical use as an objective measure of stimulus encoding by the brain, for example, in the case of cochlear implant (CI) listening. Yet, the CI-transmitted speech signal is severely spectrally degraded, rendering its amenability to neural decoding unknown. Furthermore, interplay between acoustic and linguistic factors may lead to top-down modulation of perception, thereby challenging potential audiological applications. We assess neural decoding of the speech envelope under spectral degradation with EEG in acoustically hearing listeners (n = 38; 18-35 years old) using vocoded speech. Additionally, we dissociate sensory from higher-order processing by employing intelligible (English) and non-intelligible (Dutch) stimuli. Subject-specific and group decoders were trained to reconstruct the speech envelope from held-out EEG, with decoder significance determined via random permutation testing. Whereas speech envelope reconstruction did not vary by acoustic clarity, intelligible speech was associated with better decoding accuracy in general. Results were similar across subject-specific and group analyses, with less consistent effects of spectral degradation in group decoding. Permutation tests revealed possible differences in decoder statistical significance by experimental condition. In general, while robust neural decoding was observed at the group level, variability within participants would most likely prevent the clinical use of such a measure to differentiate levels of spectral degradation and intelligibility on an individual basis.

Rejuvenating silicon probes for acute electrophysiology
Electrophysiological recording with a new probe often yields better signal quality than with a used probe. Why does the signal quality degrade after only a few experiments? Here, we considered silicon probes in which the contacts are densely packed, and each is coated with a conductive polymer that increases its surface area. We tested 12 Cambridge Neurotech silicon probes during 61 recording sessions from the brain of 3 marmosets. Out of the box, each probe arrived with an electrodeposited polymer coating on 64 gold contacts, and an impedance of around 50k Ohms. With repeated use, the impedance increased and there was a corresponding decrease in the number of well-isolated neurons. Imaging of the probes suggested that the reduction in signal quality was due to a gradual loss of the polymer coating. To rejuvenate the probes, we first stripped the contacts, completely removing their polymer coating, and then recoated them in a solution of 10 mM EDOT monomer with 32 uM PSS using a current density of about 3mA/cm2 for 30 seconds. This recoating process not only returned probe impedance to around 50k Ohms, it also yielded significantly improved signal quality during neurophysiological recordings. Thus, insertion into the brain promoted loss of the polymer that coated the contacts of the silicon probes. This led to degradation of signal quality, but recoating rejuvenated the probes.

Dissociable roles of neural pattern reactivation and transformation during recognition of words read aloud and silently: An MVPA study of the production effect
Recent work surrounding the neural correlates of episodic memory retrieval has focussed on the decodability of neural activation patterns elicited by unique stimuli. Research in this area has revealed two distinct phenomena: (i) neural pattern reactivation, which describes the fidelity of activation patterns between encoding and retrieval; (ii) neural pattern transformation, which describes systematic changes to these patterns. This study used fMRI to investigate the roles of these two processes in the context of the production effect, which is a robust episodic memory advantage for words read aloud compared to words read silently. Twenty-five participants read words either aloud or silently, and later performed old-new recognition judgements on all previously seen words. We applied multivariate analysis to compare measures of reactivation and transformation between the two conditions. We found that, compared with silent words, successful recognition of aloud words was associated with reactivation in the left insula and transformation in the left precuneus. By contrast, recognising silent words (compared to aloud) was associated with relatively more extensive reactivation, predominantly in left ventral temporal and prefrontal areas. We suggest that recognition of aloud words might depend on retrieval and metacognitive evaluation of speech-related information that was elicited during the initial encoding experience, while recognition of silent words is more dependent on reinstatement of visual-orthographic information. Overall, our results demonstrate that different encoding conditions may give rise to dissociable neural mechanisms supporting single word recognition.

Optic nerve injury impairs intrinsic mechanisms underlying electrical activity in a resilient retinal ganglion cell
Retinal ganglion cells (RGCs) are the sole output neurons of the retina and convey visual information to the brain via their axons in the optic nerve. Following an injury to the optic nerve, RGCs axons degenerate and many cells die. For example, a surgical model of compressive axon injury, the optic nerve crush (ONC), kills ~80% of RGCs after two weeks. Surviving cells are biased towards certain 'resilient' types, including several types that originally produced sustained firing to light stimulation. RGC survival may depend on activity level, and there is a limited understanding of how or why activity changes following optic nerve injury. Here we quantified the electrophysiological properties of a highly resilient RGC type, the sustained ON-Alpha RGC, seven days post-ONC with extracellular and whole-cell patch clamp recording. Both light- and current-driven firing were reduced after ONC, but synaptic inputs were largely intact. Resting membrane potential and input resistance were relatively unchanged, while voltage-gated currents were impaired, including a reduction in voltage-gated sodium channel density in the axon initial segment and function. Hyperpolarization or chelation of intracellular calcium partially rescued firing rates. These data suggest that an injured resilient RGC reduces its activity by a combination of reduced voltage-gated channel expression and function and downregulation of intrinsic excitability via a Ca2+-dependent mechanism without substantial changes in synaptic input. Reduced excitability may be due to degradation of the axon but could also be energetically beneficial for injured RGCs, preserving cellular energy for survival and regeneration.