bioRxiv Subject Collection: Neuroscience's Journal

Hippocampal representations of alternative possibilities are flexibly generated to meet cognitive demands
The cognitive ability to go beyond the present to consider alternative possibilities, including potential futures and counterfactual pasts, can support adaptive decision making. Complex and changing real-world environments, however, have many possible alternatives. Whether and how the brain can select among them to represent alternatives that meet current cognitive needs remains unknown. We therefore examined neural representations of alternative spatial locations in the rat hippocampus during navigation in a complex patch foraging environment with changing reward probabilities. We found representations of multiple alternatives along paths ahead and behind the animal, including in distant alternative patches. Critically, these representations were modulated in distinct patterns across successive trials: alternative paths were represented proportionate to their evolving relative value and predicted subsequent decisions, whereas distant alternatives were prevalent during value updating. These results demonstrate that the brain modulates the generation of alternative possibilities in patterns that meet changing cognitive needs for adaptive behavior.

Mother-child dyadic interactions shape children's social brain and theory of mind
Social cognition develops through a complex interplay between neural maturation and environmental factors, yet the neurobehavioral mechanisms underlying this process remain unclear. Using a naturalistic fMRI paradigm, we investigated the effects of age and parental caregiving on social brain development and Theory of Mind (ToM) in 50 mother-child dyads. The functional maturity of social brain networks was positively associated with age, while mother-child neural synchronization during movie viewing was related to dyadic relationship quality. Crucially, parenting and child factors interactively shaped social cognition outcomes, mediated by ToM abilities. Our findings demonstrate the dynamic interplay of neurocognitive development and interpersonal synchrony in early childhood social cognition, and provide novel evidence for Bandura's theory of social learning and reciprocal determinism. This integrative approach, bridging brain, behavior, and parenting environment, advances our understanding of the complex mechanisms shaping social cognition. The insights gained can inform personalized interventions promoting social competence, emphasizing the critical importance of nurturing parental relationships in facilitating healthy social development.

Adrenergic signaling gates astrocyte responsiveness to neurotransmitters and control of neuronal activity
How astrocytes regulate neuronal circuits is a fundamental, unsolved question in neurobiology. Nevertheless, few studies have explored the rules that govern when astrocytes respond to different neurotransmitters in vivo and how they affect downstream circuit modulation. Here, we report an unexpected mechanism in Drosophila by which G-protein coupled adrenergic signaling in astrocytes can control, or ''gate,'' their ability to respond to other neurotransmitters. Further, we show that manipulating this pathway potently regulates neuronal circuit activity and animal behavior. Finally, we demonstrate that this gating mechanism is conserved in mammalian astrocytes, arguing it is an ancient feature of astrocyte circuit function. Our work establishes a new mechanism by which astrocytes dynamically respond to and modulate neuronal activity in different brain regions and in different behavioral states.

GABAergic neuron dysregulation in a human neurodevelopmental model for major psychiatric disorders
GABA dysfunction is a major hypothesis for the biological basis of schizophrenia with indirect supporting evidence from human post-mortem brain and genetic studies. Patient-derived induced pluripotent stem cells (iPSCs) have emerged as a valuable platform for modeling psychiatric disorders, and previous modeling has revealed glutamatergic synapse deficits. Whether GABAergic synapse properties are affected in patient-derived human neurons and how this impacts neuronal network activity remain poorly understood. Here we optimized a protocol to differentiate iPSCs into highly enriched ganglionic eminence-like neural progenitors and GABAergic neurons. Using a collection of iPSCs derived from patients of psychiatric disorders carrying a Disrupted-in-Schizophrenia 1 (DISC1) mutation and their unaffected family member, together with respective isogenic lines, we identified mutation-dependent deficits in GABAergic synapse formation and function, a phenotype similar to that of mutant glutamatergic neurons. However, mutant glutamatergic and GABAergic neurons contribute differentially to neuronal network excitability and synchrony deficits. Finally, we showed that GABAergic synaptic transmission is also defective in neurons derived from several idiopathic schizophrenia patient iPSCs. Transcriptome analysis further showed some shared gene expression dysregulation, which is more prominent in DISC1 mutant neurons. Together, our study supports a functional GABAergic synaptic deficit in major psychiatric disorders.

A minor impact of VGLUT1 expression level on quantal size revealed through the characterization of VGLUT1mEos2 knock-down new mouse model
Synaptic vesicles (SVs) are small organelles secreting neurotransmitters at synapses. By fusing a photoactivated fluorescent protein to VGLUT1, we generated a VGLUT1mEos2 knock-in mouse. VGLUT1mEos2 knock-in mice are viable and healthy, but exhibit a severe reduction in VGLUT1 expression levels. Using VGLUT1mEos2 expressing neurons, we established paradigms to trace individual SV mobility at the single-molecule level or via massive photoconversion. Hippocampal neurons with significantly diminished VGLUT1 expression maintain unaltered miniature glutamate release characteristics in terms of quantal size and frequency. We demonstrate that VGLUT1 expression level is not correlated in a linear fashion with the vesicular glutamate content. In conclusion, the VGLUT1mEos2 mouse line serves as a powerful tool for exploring SV mobility properties and elucidating the contributions of VGLUT1 to excitatory neurotransmission and cognitive processes.

Brain inflammation and cognitive decline induced by spinal cord injury can be reversed by spinal cord cell transplants
Spinal cord injuries (SCIs) affect between 250,000 and 500,000 people worldwide each year, most commonly due to road accidents or falls. These injuries result in permanent disabilities, the severity and impact of which are directly related to the extent and location of the injury. Recent studies have also shown that SCIs can lead to cognitive disorders due to inflammation in the brain. From a therapeutic perspective, numerous treatments have been explored, including cell therapy. It has been established that a common mechanism across various cellular transplant models is the modulation of inflammation at the injury site. However, it remains unclear whether the immunomodulatory effects observed in the spinal cord also extend to the brain. To test this hypothesis, we induced SCI in wild-type mice and treated them with transplants of differentiated cells, specifically olfactory ensheathing cells, or stem cells, such as mesenchymal stem cells. Our results demonstrate that both types of transplants can reverse cognitive disorders induced by SCI. Additionally, we found that these cellular transplants modulate brain inflammation and increase neuronal density in the hippocampus. To our knowledge, this is the first study to show that cells transplanted into the spinal cord can modulate the inflammatory response in the brain, thereby reversing the negative effects of injury on brain function following SCI. These findings underscore the complex interactions between the brain and spinal cord under both physiological and pathological conditions.

Neural substrates for saccadic modulation of visual representations in mouse superior colliculus
How do sensory systems account for stimuli generated by natural behavior? We addressed this question by examining how an ethologically relevant class of saccades modulates visual representations in the mouse superior colliculus (SC), a key center for sensorimotor integration. We quantified saccadic modulation by recording SC responses to visual probes presented at stochastic saccade-probe latencies. Saccades significantly impacted population representations of the probes, with early enhancement that began prior to saccades and pronounced suppression for several hundred milliseconds following saccades, independent of units' visual response properties or directional tuning. To determine the cause of saccadic modulation, we presented fictive saccades that simulated the visual experience during saccades without motor output. Some units exhibited similar modulation by fictive and real saccades, suggesting a sensory-driven origin of saccadic modulation, while others had dissimilar modulation, indicating a motor contribution. These findings advance our understanding of the neural basis of natural visual coding.

Higher-order and distributed synergistic functional interactions encode information gain in goal-directed learning
The ability to create beliefs about the consequences of our actions, also known as goal-directed learning, is a key facet of cognition and it provides the basis for rational decision-making. Goal-directed learning arises from a distributed neural circuit including the prefrontal, posterior parietal and temporal cortices. However, the role of cortico-cortical functional interactions remains unclear. To tackle this question, we combined information decomposition theory with human magnetoencephalography (MEG) and studied whether and how learning signals are encoded through neural interactions. Our findings revealed that 'information gain' - or the decrease in uncertainty regarding the causal relationship between an action and its consequence - is represented within a distributed cortical network, incorporating the visual, parietal, lateral prefrontal, and ventromedial/orbital prefrontal cortices. Remarkably, cortico-cortical interactions encoded information gain in a synergistic manner, beyond what individual regions represented alone. Synergistic interactions encoded information gain at the level of pairwise and higher-order relations, such as triplets and quadruplets. Higher-order synergistic interactions were characterised by long-range relations gravitating over the ventromedial and orbitofrontal cortices, which played a receiving role in the broadcasting of information gain over cortical circuits. Overall, the current study provides evidence that information gain is encoded in both synergistic and higher-order functional interactions, as well as through the broadcasting of information gain signals toward the prefrontal reward circuitry. Moreover, our research offers a new perspective on how information relevant to cognition is encoded and broadcasted within distributed cortical networks and brain-wide dynamics.

Identification of Intrinsic Features for Cortical Separability of Human and Mouse Neurons
This work introduces a novel framework for holistic comparative analysis of cortical regions in mouse and human brains at single-neuron resolution, with a primary focus on the morphological and molecular characteristics of neurons. To do so, we generated one of the largest dendritic reconstruction datasets of cortical neurons to date, comprising 2,363 human neurons and 16,011 mouse neurons from the frontal, parietal, and temporal lobes, followed by establishing a rigorous procedure to identify anatomically and functionally corresponding brain regions with minimal variability in brain mapping. Additionally, we leveraged single nucleus/cell transcriptomic data from independent groups to validate the molecular correspondence of the brain regions identified in this study. The significance of these anatomically, functionally, and molecularly corresponding mouse-human region pairs is highlighted by examining the intrinsic features of their respective cortical regions. Our findings reveal that human neuron branching patterns differ dramatically from those in mouse brains, particularly in terms of dendritic branching frequency and normalized dendritic branching intervals. This difference is pronounced in the frontal and temporal lobes, underscoring the distinct neuronal architectures between the two species. At the single-neuron level, we found that neurons from the human frontal and parietal lobes are six times more separable than those from the same regions in mouse brains. This heightened separability is also observed between the frontal and temporal lobes, as well as between the parietal and temporal lobes in humans. We thoroughly explored the entire morphological feature space, along with its characteristic subspaces, and consistently found this distinct separability. Remarkably, this neuronal separability can be partially recapitulated when examining the global functional states of these brain lobes-using newly acquired Electroencephalography (EEG) and Magnetoencephalography (MEG) signals as physiological measures-as well as their global metabolic states, molecular profiles, and cortical geometry. These findings suggest that our comparative analysis of single-neuron intrinsic features could serve as a valuable foundation for future comprehensive studies of cross-species brain structures and functions.

Auditory decision-making deficits after permanent noise-induced hearing loss
Loud noise exposure is one of the leading causes of permanent hearing loss. Individuals with noise-induced hearing loss (NIHL) suffer from speech comprehension deficits and experience impairments to cognitive functions such as attention and decision-making. Here, we tested whether a specific sensory deficit, NIHL, can directly impair auditory cognitive function. Gerbils were trained to perform an auditory decision-making task that involves discriminating between slow and fast presentation rates of amplitude-modulated (AM) noise. Decision-making task performance was assessed across pre- versus post-NIHL sessions within the same gerbils. A single exposure session (2 hours) to loud broadband noise (120 dB SPL) produced permanent NIHL with elevated threshold shifts in auditory brainstem responses (ABRs). Following NIHL, decision-making task performance was tested at sensation levels comparable to those prior to noise exposure in all animals. Our findings demonstrate NIHL diminished perceptual acuity, reduced attentional focus, altered choice bias, and slowed down evidence accumulation speed. Finally, video-tracking analysis of motor behavior during task performance demonstrates that NIHL can impact sensory-guided decision-based motor execution. Together, these results suggest that NIHL impairs the sensory, cognitive, and motor factors that support auditory decision-making.

Bayesian inference by visuomotor neurons in prefrontal cortex
Perceptual judgements of the environment emerge from the concerted activity of neural populations in decision making areas downstream of sensory cortex. When the sensory input is ambiguous, perceptual judgements can be biased by prior expectations shaped by environmental regularities. These effects are examples of Bayesian inference, a reasoning method in which prior knowledge is leveraged to optimize uncertain decisions. However, it is not known how decision making circuits combine sensory signals and prior expectations to form a perceptual decision. Here, we study neural population activity in the prefrontal cortex of macaque monkeys trained to report perceptual judgments of ambiguous visual stimuli under two different stimulus distributions. We analyze the component of the neural population response that represents the formation of the perceptual decision (the decision variable, DV), and find that its dynamical evolution reflects the integration of sensory signals and prior expectations. Prior expectations impact the DV's trajectory both before and during stimulus presentation such that DV trajectories with a smaller dynamic range result in more biased and less sensitive perceptual decisions. These results reveal a mechanism by which prefrontal circuits can execute Bayesian inference.

Repetition suppression for mirror images of objects and not Braille letters in the ventral visual stream of congenitally blind individuals
Mirror-invariance effect describes the cognitive tendency to perceive mirror-image objects as identical. Mirrored letters, however, are distinct orthographic units and must be identified as different. Mirror-invariance must be broken to enable efficient reading. Consistent with this phenomenon, a small, localized region in the ventral visual stream, the Visual Word Form Area (VWFA), exhibits repetition suppression to identical and mirror pairs of objects but only to identical pairs of letters. The ability of congenitally blind individuals to break mirror invariance for pairs of mirrored Braille letters has been demonstrated behaviorally. However, its neural underpinnings have not yet been investigated. Here, in an fMRI repetition suppression paradigm, congenially blind individuals (both sexes) recognized pairs of everyday objects and Braille letters in identical (p & p), mirror (p & q), and different (p & z) orientations. We found repetition suppression for identical and mirror pairs of everyday objects in the parietal and ventral-lateral occipital cortex, indicating that mirror-invariant object recognition engages the ventral visual stream in tactile modality as well. However, repetition suppression for identical but not mirrored pairs of Braille letters was found in the left parietal cortex and the lateral occipital cortex but not in the VWFA. These results suggest notable differences in reading-related orthographic processes between sighted and blind individuals, with the LOC region in the latter being a potential hub for letter-shape processing.

Pleiotrophin deletion prevents high-fat diet-induced cognitive impairment, glial responses, and alterations of the perineuronal nets in the hippocampus
Obesity and metabolic disorders, such as metabolic syndrome (MetS) facilitate the development of neurodegenerative diseases and cognitive decline. Persistent neuroinflammation plays an important role in this process. Pleiotrophin (PTN) is a cytokine that regulates energy metabolism and high-fat diet (HFD)-induced neuroinflammation, suggesting that PTN could play an important role in the connection between obesity and brain alterations, including cognitive decline. To test this hypothesis, we used an HFD-induced obesity model in Ptn genetically deficient mice (Ptn-/-). First, we confirmed that Ptn deletion prevents HFD-induced obesity. Our findings demonstrate that feeding wild-type (Ptn+/+) mice with HFD for 6 months results in short- and long-term memory loss in the novel object recognition task. Surprisingly, we did not observe any sign of cognitive impairment in Ptn-/- mice fed with HFD. In addition, we observed that HFD induced microglial responses, astrocyte depletion, and perineuronal nets (PNNs) alterations in Ptn+/+ mice, while these effects of HFD were mostly prevented in Ptn-/- mice. These results show a crucial role of PTN in metabolic responses and brain alterations induced by HFD and suggest the PTN signalling pathway as a promising therapeutic target for brain disorders associated with MetS.

Low intensity pulsed ultrasound activates excitatory synaptic networks in cultured hippocampal neurons
Ultrasound can non-invasively penetrate deep into brain for neuromodulation and has demonstrated good potential for clinical application. Excitation or inhibition of neurons by ultrasound has been reported, but the underlying mechanisms are largely unknown. So far most in vitro studies have focused on the activation of individual neurons by ultrasound with calcium imaging. As the focal region of ultrasound is typically millimeter or submillimeter size, it is important to investigate yet so far unclear how the mechanical effects of ultrasound would influence on the synaptic circuit activity of neurons. Methods: Low-intensity pulsed ultrasound (LIPUS) (25 MHz, 5% duty cycle, 5 Hz pulse repetition frequency, 0.4 - 1.6 W/cm2) was used to stimulate cultured hippocampal neurons. Action potentials and excitatory postsynaptic currents were recorded in individual cells with the whole-cell patch-clamp technique. We also simultaneously imaged intracellular calcium, along with neuronal electrical signals, to resolve neuronal network dynamics during LIPUS. Results: Excitatory postsynaptic currents (EPSCs) were evoked by LIPUS in high-density neuronal cultures. Both the frequency and amplitude of EPSCs increased, indicating enhanced glutamatergic synaptic transmission. The probability of evoking responses, as well as the total charge of EPSCs evoked by ultrasound, increased with ultrasound intensity. Mechanistic analysis reveals that extracellular calcium influx, action potential (AP) firing and synaptic transmission are necessary for the responses to ultrasound in the high-density culture. In contrast, EPSCs were not enhanced in cultures with low densities of neurons. Simultaneous calcium imaging of neuronal network activity indicated that recurrent excitatory network activity is recruited during ultrasound stimulation in high-density cultures. Conclusion: Ultrasound can activate recurrent neuronal network activity, caused by excitatory synaptic transmission, over tens to hundreds of seconds. Our study provides insights into the mechanisms involved in the response of the brain to ultrasound and illuminates the potential to use ultrasound to regulate synaptic function in neurological disorders that involve synaptic dysfunction, such as Parkinson's disease and Alzheimer's disease. Keywords: Ultrasound neuromodulation, synaptic transmission, electrophysiology, calcium imaging, neuronal networks

Somatosensory cortex and body representation: Updating the motor system during a visuo-proprioceptive cue conflict
The brain's representation of hand position is critical for voluntary movement. Representation is multisensory, relying on both visual and proprioceptive cues. When these cues conflict, the brain recalibrates its unimodal estimates, shifting them closer together to compensate. Converging lines of evidence from research in perception, behavior, and neurophysiology suggest that such updates to body representation must be communicated to the motor system to keep hand movements accurate. We hypothesized that primary somatosensory cortex (S1) plays a crucial role in conveying the proprioceptive aspects of the updated body representation to the motor system. We tested this hypothesis in two experiments. We predicted that proprioceptive, but not visual, recalibration would be associated with change in short latency afferent inhibition (SAI), a measure of sensorimotor integration (influence of sensory input on motor output) (Expt. 1). We further predicted that modulating S1 activity with repetitive transcranial magnetic stimulation (TMS) should affect variance and recalibration associated with the proprioceptive estimate of hand position, but have no effect on the visual estimate (Expt. 2). Our results are consistent with these predictions, supporting the idea that (1) S1 is indeed a key region in facilitating motor system updates based on changes in body representation, and (2) this function is mediated by unisensory (proprioceptive) processing, upstream of multisensory visuo-proprioceptive computations. Other aspects of the body representation (visual and multisensory) may be conveyed to the motor system via separate pathways, e.g. from posterior parietal regions to motor cortex.

BDNF augmentation reverses cranial radiation therapy-induced cognitive decline and neurodegenerative consequences
Cranial radiation therapy (RT) for brain cancers is often associated with the development of radiation-induced cognitive dysfunction (RICD). RICD significantly impacts the quality of life for cancer survivors, highlighting an unmet medical need. Previous human studies revealed a marked reduction in plasma brain-derived neurotrophic factor (BDNF) post-chronic chemotherapy, linking this decline to a substantial cognitive dysfunction among cancer survivors. Moreover, riluzole (RZ)-mediated increased BDNF in vivo in the chemotherapy-exposed mice reversed cognitive decline. RZ is an FDA-approved medication for ALS known to increase BDNF in vivo. In an effort to mitigate the detrimental effects of RT-induced BDNF decline in RICD, we tested the efficacy of RZ in a cranially irradiated (9 Gy) adult mouse model. Notably, RT-exposed mice exhibited significantly reduced hippocampal BDNF, accompanied by increased neuroinflammation, loss of neuronal plasticity-related immediate early gene product, cFos, and synaptic density. Spatial transcriptomic profiling comparing the RT+Veh with the RT+RZ group showed gene expression signatures of neuroprotection of hippocampal excitatory neurons post-RZ. RT-exposed mice performed poorly on learning and memory, and memory consolidation tasks. However, irradiated mice receiving RZ (13 mg/kg, drinking water) for 6-7 weeks showed a significant improvement in cognitive function compared to RT-exposed mice receiving vehicle. Dual-immunofluorescence staining, spatial transcriptomics, and biochemical assessment of RZ-treated irradiated brains demonstrated preservation of synaptic integrity and neuronal plasticity but not neurogenesis and reduced neuroinflammation concurrent with elevated BDNF levels and transcripts compared to vehicle-treated irradiated brains. In summary, oral administration of RZ represents a viable and translationally feasible neuroprotective approach against RICD.

How neural network structure alters the brain's self-organized criticality
In recent years, the "brain critical hypothesis" has been proposed in the fields of complex systems science and statistical physics, suggesting that the brain acquires functions such as information processing capabilities near the critical point, which lies at the boundary between disorder and order. As a mechanism for maintaining this critical state, a feedback system called "self-organized criticality (SOC)" has been proposed, where parameters related to brain function, such as synaptic plasticity, are maintained by internal rules without external adjustments. Additionally, the structure of neural networks plays an important role in information processing, with healthy neural networks being characterized by properties such as small-worldness, scale-freeness, and modularity. However, it has also been pointed out that these properties may be lacking in cases of neurological disorders. In this study, we used a mathematical model to investigate the possibility that differences in neural network structures could lead to brain dysfunction through SOC. As a result, it became clear that the synaptic plasticity conditions that maximize information processing capabilities vary depending on the network structure. Notably, when the network possesses only a scale-free structure, a phenomenon known as the Dragon king -associated with abnormal neural activity - was observed. These findings suggest that the maintenance of neural dynamics equilibrium differs depending on the structural characteristics of the neural network, and that in structures with hub nodes, such as scale-free networks, imbalances in neural dynamics may occur, potentially negatively impacting brain function.

A stolen future: aberrant hippocampal neurogenesis produces glial cells in epilepsy
Adult hippocampal neurogenesis is disturbed in epilepsy. The increased neuronal activity in the epileptic brain leads to an increased production of newborn cells, increased mossy fibre sprouting and altered integration of new neurons within the hippocampus. Here, we set out to investigate increased astrocyte numbers following status epilepticus. We used immunolabelling of brain sections from the mouse intra-amygdala kainic acid model of epilepsy and publicly available single cell RNA sequencing datasets to assess newborn cells in the dentate gyrus. Similar to published series we found on increased number of reactive astrocytes present in the epileptic hippocampus. Additionally, we identified a cell population that expressed neurogenesis (doublecortin) and astrocyte (glial fibrillary acidic protein) markers in the epileptic brain, both in mouse and in human tissue. We further evaluated the expression profile of these cells. Immunolabelling showed expression of mature astrocyte markers aquaporin 4 and glutamate transporter-1. The single cell RNA sequencing data highlighted expression of neurogenesis and astrocyte markers in the doublecortin/glial fibrillary acidic protein-expressing cells. In conclusion, epilepsy pushes early neuroblasts to fate-switch to an astrocyte lineage as seen in the kainic acid-induced mouse model and in human resected brain tissue. Further understanding how neurogenesis is altered in epilepsy and whether the neuroblast fate-switch can be reverted will help in finding novel therapy strategies for epilepsy and other neurological diseases associated with aberrant adult hippocampal neurogenesis.

Distinct classes of antidepressants commonly act to shape pallidal structure and function in mice
Antidepressants, including selective serotonin reuptake inhibitors (SSRIs), ketamine, and psilocybin, are effective for treating depression despite their distinct modes of action. We hypothesized that their underlying mechanisms of action are shared. Mice were administered escitalopram (15 mg/kg daily for 3 weeks, 21 mice), R/S/racemic ketamine (10 mg/kg, single injection, 22 mice), or psilocin (1 mg/kg, single injection, 22 mice). Electroconvulsive stimulation (9 times for 3 weeks, 12 mice) and saline were used as controls. After structural magnetic resonance imaging (MRI) of fixed brains, voxel based morphometry was conducted to assess brain wide volumetric changes. A single dose of ketamine or psilocin was sufficient to induce MRI detectable volume changes. All antidepressants increased the volume in the nucleus accumbens, ventral pallidum, and external globus pallidus and decreased the volume in the mediodorsal thalamus, which is distinct from the changes observed with electroconvulsive stimulation. We identified microstructural and molecular changes using super-resolution microscopy and imaging mass spectrometry, respectively. Pallidal volumetric increases were associated with hypertrophy of striatal medium spiny neuron terminals and increased GABA content. We experimentally addressed whether the overexpression of the vesicular GABA transporter (VGAT) reproduced these changes. The overexpression of striatal VGAT reproduced these structural changes. R ketamine, SR ketamine, and psilocin induced more pronounced ventral pallidum hypertrophy, and SSRIs and S ketamine induced globus pallidus hypertrophy. We discovered shared pallidum centered structural and molecular changes among various antidepressants, which possibly potentiate the striato pallidial inhibition associated with antidepressant action. Our data support visualizing antidepressant responses using pallidum centered GABA MR spectroscopy or structural MRI.

Absent, but not glucocorticoid-modulated, corticotropin-releasing hormone (Crh) regulates anxiety-like behaviors in mice
The hypothalamic-pituitary-adrenal (HPA) axis is a well characterized endocrine response system. Hypothalamic Crh in the paraventricular nucleus of the hypothalamus (PVH) initiates HPA axis signaling to cause the release of cortisol (or corticosterone in rodents) from the adrenal gland. PVH-specific deletion of Crh reduces anxiety-like behaviors in mice. Here we report that manipulation of PVH Crh expression in primary adrenal insufficiency or by dexamethasone (DEX) treatment do not alter mouse anxiety behaviors. In Experiment 1, we compared wildtype (WT) mice to those with primary adrenal insufficiency (MrapKO) or global deletion of Crh (CrhKO). We analyzed behaviors using open field (OF) and elevated plus maze (EPM), PVH Crh mRNA expression by spatial transcriptomics, and plasma ACTH and corticosterone after a 15-minute restraint test with ELISAs. EPM analysis showed CrhKO mice were less anxious than WT and MrapKO mice, and MrapKO mice had no distinguishing behavioral phenotype. In Experiment 2, we evaluated HPA axis habituation to chronically elevated Crh expression by comparing mice treated with 5-8 weeks of DEX with those similarly treated followed by DEX withdrawal for 1 week. All mice regardless of genotype and treatment showed no significant behavioral differences. Our findings suggest that reduced anxiety associated with low Crh expression requires extreme deficiency, perhaps outside of those PVH Crh neurons negatively regulated by glucocorticoids. If these findings extend to humans, they suggest that increases in Crh expression with primary adrenal insufficiency, or decreases with exogenous glucocorticoid therapy, may not alter anxiety behaviors via modulation of Crh expression.

A toolbox for ablating excitatory and inhibitory synapses
Recombinant optogenetic and chemogenetic proteins that manipulate neuronal activity are potent tools for activating and inhibiting neuronal circuit function. However, there are few analogous tools for manipulating the structure of neural circuits. Here, we introduce three rationally designed genetically encoded tools that use E3 ligase-dependent mechanisms to trigger the degradation of synaptic scaffolding proteins, leading to functional ablation of synapses. First, we developed a constitutive excitatory synapse ablator, PFE3, analogous to the inhibitory synapse ablator GFE3. PFE3 targets the RING domain of the E3 ligase Mdm2 and the proteasome-interacting region of Protocadherin 10 to the scaffolding protein PSD-95, leading to efficient ablation of excitatory synapses. In addition, we developed a light-inducible version of GFE3, paGFE3, using a novel photoactivatable complex based on the photocleavable protein PhoCl2c. paGFE3 degrades Gephyrin and ablates inhibitory synapses in response to 400 nm light. Finally, we developed a chemically inducible version of GFE3, chGFE3, which degrades inhibitory synapses when combined with the bio-orthogonal dimerizer, HaloTag ligand-trimethoprim. Each tool is specific, reversible, and capable of breaking neural circuits at precise locations.

Organellular imaging in vivo reveals a depletion of endoplasmic reticular calcium during post-ictal cortical spreading depolarization
During cortical spreading depolarization (CSD), neurons exhibit a dramatic increase in cytosolic calcium, which may be integral to CSD-mediated seizure termination. This calcium increase greatly exceeds that during seizures, suggesting the calcium source may not be solely extracellular. Thus, we sought to determine if the endoplasmic reticulum (ER), the largest intracellular calcium store, is involved. We developed a two-photon calcium imaging paradigm to simultaneously record the cytosol and ER during seizures in awake mice. Paired with direct current recording, we reveal that CSD can manifest as a slow post-ictal cytosolic calcium wave with a concomitant depletion of ER calcium that is spatiotemporally consistent with a calcium-induced calcium release. Importantly, we observed both naturally occurring and electrically induced CSD suppressed post-ictal epileptiform activity. Collectively, this work links ER dynamics to CSD, which serves as an innate process for seizure suppression and a potential mechanism underlying therapeutic electrical stimulation for epilepsy.

High-speed 3D Imaging with 25-Camera Multifocus Microscope
We here report an aberration corrected 25 plane camera array Multifocus microscope (M25) for high speed, high resolution widefield optical microscopy in three spatial dimensions (3D). We demonstrate live imaging of 25 plane 3D volumes of up to 180x180x50um at >100 volumes per second. 3D data is recorded simultaneously by an array of 25 small, sensitive, synchronized machine vision cameras. M25 employs aberration corrected Multifocus microscopy, an optical method where diffractive Fourier optics are used for multiplexing and refocusing light, with a simplified design for chromatic dispersion correction where a corrective diffractive grating is placed on each camera in the array. This elegant architecture for chromatic correction will be applicable in a broad range of diffractive imaging applications. M25 is a powerful optical tool for high speed 3D microscopy in that it allows both non invasive, label free bright field and highly sensitive fluorescence microscopy. We showcase M25 capabilities in 3D particle tracking, bright field and fluorescence imaging in D. melanogaster, and locomotion and neural activity studies in C. elegans.

Effects of age on resting-state cortical networks
Magnetoencephalography recordings of functional brain activity reveal large-scale cortical networks that are associated with cognition. The correlation of individualised networks with age and cognitive performance (age effects and cognitive performance effects respectively) was studied using a large cross-sectional healthy cohort (N=612, 18-88 years old) and accounting for a comprehensive set of confounds. Age effects were found in time-averaged functional networks in five canonical frequency bands (delta, theta, alpha, beta, gamma) that are consistent with the posterior-anterior shift with age observed in functional magnetic resonance imaging. Evidence from cognitive performance effects in time-averaged networks suggested the importance of maintaining alpha-band activity for cognitive health. A more detailed description of the functional activity was obtained by adopting an established machine learning approach (the Hidden Markov Model). Ten transient large-scale cortical networks with fast dynamics (~100 ms) were identified, which provided insight into age and cognitive performance effects that were not observed in the time-averaged analyses. The time spent in most networks increased with age, whereas the time spent in frontal networks decreased. The cognitive performance effects for the transient networks suggested that age effects in the frontal networks are compensatory. Thus, our study suggests both the maintenance of functional activity (lesser age effects) and the recruitment of compensatory functional activity can co-occur to produce good cognitive performance in older individuals. The time-averaged and transient functional networks have been made publicly available as a resource.

Motor preparation tracks decision boundary crossing in temporal decision-making
Interval timing, the ability of animals to estimate the passage of time, is thought to involve diverse neural processes rather than a single central "clock" (Paton & Buonomano, 2018). Each of the different processes engaged in interval timing follows a different dynamic path, according to its specific function. For example, attention tracks anticipated events, such as offsets of intervals (Rohenkohl & Nobre, 2011), while motor processes control the timing of the behavioral output (De Lafuente et al., 2024). Hence, different processes provide complimentary perspectives on mechanisms of time perception. The temporal bisection task, where participants categorize intervals as "long" or "short", is thought to rely on the same mechanisms as other perceptual decisions (Balci & Simen, 2014). In line with this hypothesis, we previously described an EEG potential that tracks the formation of decision following the end of the timed interval (Ofir & Landau, 2022). Here, we track the dynamics of motor preparation to investigate the formation of decision within the timed interval. In contrast to typical perceptual decisions, where motor plans for all response alternatives are prepared simultaneously (Shadlen & Kiani, 2013), we find that different temporal decisions develop sequentially. While preparation for "long" responses was already underway before interval offset, no preparation was found for "short" responses. Furthermore, within intervals categorized as "long", motor preparation was stronger at interval offset for faster responses. Our findings shed light on the unique dynamics of temporal decisions and demonstrate the importance of considering neural activity in timing tasks from multiple perspectives.

Amyloid-β-induced Alteration of Fast and Localized Calcium Elevations in Cultured Astrocytes
Alzheimer's disease (AD) is a progressive neurodegenerative disorder that causes cognitive decline. Uncovering the mechanisms of neurodegeneration in the early stages is essential to establish a treatment for AD. Recent research has proposed the hypothesis that amyloid-{beta} (A{beta}) oligomers elicit an excessive glutamate release from astrocytes toward synapses through intracellular free Ca2+ ([Ca2+]i) elevations in astrocytes, finally resulting in neuronal dendritic spine loss. Under physiological conditions, astrocytic [Ca2+]i elevations range spatially from microdomains to network-wide propagation and temporally from milliseconds to tens of seconds. Astrocytic localized and fast [Ca2+]i elevations might correlate with glutamate release; however, the A{beta}-induced alteration of localized, fast astrocytic [Ca2+]i elevations remains unexplored. In this study, we quantitatively investigated the A{beta} dimers-induced changes in the spatial and temporal patterns of [Ca2+]i in a primary culture of astrocytes by two-photon excitation spinning-disk confocal microscopy. The frequency of fast [Ca2+]i elevations occurring locally in astrocytes ([≤]0.5 s, [≤]35 m2) and [Ca2+]i event occupancy relative to cell area significantly increased after exposure to A{beta} dimers. The effect of A{beta} dimers appeared dose-dependently above 500 nM, and these A{beta} dimers-induced [Ca2+]i elevations were primarily mediated by a metabotropic purinergic receptor (P2Y1 receptor) and Ca2+ release from the endoplasmic reticulum. Our findings suggest that the A{beta} dimers-induced alterations and hyperactivation of astrocytic [Ca2+]i is a candidate cellular mechanism in the early stages of AD.

Why do we have so many excitatory neurons?
Approximately four in five neurons are excitatory. This is true across functional regions and species. Why do we have so many excitatory neurons? Little is known. Here we provide a normative answer to this question. We designed a task-agnostic, learning-independent and experiment-testable measurement of functional complexity, which quantifies the network's ability to solve complex problems. Using the first neuron level full connectome of a species - the larva Drosophila - we discovered the optimal Excitatory-Inhibitory (E-I) ratio that maximizes the functional complexity: 75-81% percentage of neurons are excitatory. This number is consistent with the true distribution observed via scRNA-seq. We found that the abundance of excitatory neurons confers an advantage in functional complexity, but only when inhibitory neurons are highly connected. In contrast, when the E-I identities are sampled uniformly (not dependent on connectivity), the optimal E-I ratio falls around equal population size, and its overall achieved functional complexity is sub-optimal. Our functional complexity measurement offers a normative explanation for the over-abundance of excitatory neurons in the brain. We anticipate that this approach will further uncover the functional significance of various neural network structures.

The endocannabinoid 2-arachidonoylglycerol is released and transported on demand via extracellular microvesicles
While it is known that endocannabinoids (eCB) modulate multiple neuronal functions, the molecular mechanism governing their release and transport remains elusive. Here, we propose an 'on-demand release' model, wherein the formation of microvesicles, a specific group of extracellular vesicles (EVs) containing the eCB, 2-arachidonoylglycerol (2-AG), is the rate-limiting step. A co-culture model system that combines a reporter cell line expressing the fluorescent eCB sensor, GRABeCB2.0, and neuronal cells revealed that neurons release EVs containing 2-AG, but not anandamide, in a stimulus-dependent process regulated by PKC, DAGL, Arf6, and which was sensitive to inhibitors of eCB facilitated diffusion. A vesicle contained approximately 2000 2-AG molecules. Accordingly, hippocampal eCB-mediated synaptic plasticity was modulated by Arf6 and transport inhibitors. This 'on demand release' model, supported by mathematical analysis, offers a cohesive framework for understanding eCB signaling at the molecular level and suggests that microvesicles carrying signaling lipids regulate neuronal functions in parallel to canonical synaptic vesicles.

CX3CR1 modulates migration of resident microglia towards brain injury
Microglia are innate immune cells of the central nervous system (CNS). They extend their processes towards and migrate towards injuries in vivo. However, whether the fractalkine receptor (CX3CR1) influences microglial migration remains unknown. Label-free proteomic profiling predicted changes in RHO-signaling activity that hint at dysregulated cytoskeleton signaling in Cx3cr1-deficient murine cortex tissue. To further investigate microglial migration, we carried out 4-hour interval two-photon in vivo imaging for 72 hours after a laser lesion in the cortex. Cx3cr1-deficient microglia showed enhanced migration towards the lesion. Additionally, length and velocity of microglial fine processes extending towards the lesion were increased in Cx3cr1-deficient microglia. Migration remained unchanged in Ccr2-deficient mice, indicating that monocyte-derived macrophages/microglia did not contribute to microglia accumulation around the lesion. These results demonstrate microglia migration towards CNS injury and suggest CX3CR1 as a modulator of this. Manipulating microglia migration via CX3CR1 therefore is a potential target for treatment of CNS-injury.

Distinct Disruptions in CA1 and CA3 Place Cell Function in Alzheimer's Disease Mice
The hippocampus, a critical brain structure for spatial learning and memory, is susceptible to neurodegenerative disorders such as Alzheimer's disease (AD). The APPswe/PSEN1dE9 (APP/PS1) transgenic mouse model is widely used to study the pathology of AD. Although previous research has established AD-associated impairments in hippocampal-dependent learning and memory, the neurophysiological mechanisms underlying these cognitive dysfunctions remain less understood. To address this gap, we investigated the activities of place cells in both CA1 and CA3 hippocampal subregions, which have distinct yet complementary computational roles. Behaviorally, APP/PS1 mice demonstrated impaired spatial recognition memory compared to wild-type (WT) mice in the object location test. Physiologically, place cells in APP/PS1 mice showed deterioration in spatial representation compared to WT. Specifically, CA1 place cells exhibited significant reductions in coherence and spatial information, while CA3 place cells displayed a significant reduction in place field size. Both CA1 and CA3 place cells in APP/PS1 mice also showed significant disruptions in their ability to stably encode the same environment. Furthermore, the burst firing properties of these cells were altered to forms correlated with reduced cognition. Additionally, the theta rhythm was significantly attenuated in CA1 place cells of APP/PS1 mice compared to WT. Our results suggest that distinct alteration in the physiological properties of CA1 and CA3 place cells, coupled with disrupted hippocampal theta rhythm in CA1, may collectively contribute to impaired hippocampal-dependent spatial learning and memory in AD.

Embodied processing in whisker somatosensory cortex during exploratory behaviour in freely moving mice
Sensory systems have evolved to solve computational challenges that animals face during behaviour in their natural environments. To illuminate how sensory cortex operates under such conditions, we investigated the function of neurons in whisker-related Somatosensory Cortex (wS1) of freely moving mice, engaged in tactile exploratory behaviour. By recording neural activity from wS1 whilst tracking the mouse body in 3D, we found that wS1 neurons are substantially modulated by body state (configuration of individual body-parts and their derivatives), even in the absence of whisker afferent input. Most neurons were modulated by multiple dimensions of body state, with the most prominently encoded being the angle of the head to the body and locomotion speed. Overall, our data suggest that sensory cortex functions as an embodied representation, which integrates signals from its associated sense organ within a body schema.

Whisker deprivation triggers a distinct form of cortical homeostatic plasticity that is impaired in the Fmr1 KO
Mouse models of Fragile X Syndrome (FXS) have demonstrated impairments in excitatory and inhibitory sensory-evoked neuronal firing. Homeostatic plasticity, which encompasses a set of mechanisms to stabilize baseline activity levels, does not compensate for these changes in activity. Previous work has shown that impairments in homeostatic plasticity are observed in FXS, including deficits in synaptic scaling and intrinsic excitability. Here, we aimed to examine how homeostatic plasticity is altered in vivo in an Fmr1 KO mouse model following unilateral whisker deprivation (WD). We show that WD in the wild type leads to an increase in the proportion of L5/6 somatosensory neurons that are recruited, but this does not occur in the KO. In addition, we observed a change in the threshold of excitatory neurons at a later developmental stage in the KO. Compromised homeostatic plasticity in development could influence sensory processing and long-term cortical organization.

Leg compliance is required to explain the ground reaction force patterns and speed ranges in different gaits
Two simple models, vaulting over stiff legs and rebounding over compliant legs, are employed to describe the mechanics of legged locomotion. It is agreed that compliant legs are necessary for describing running and that legs are compliant while walking. Despite this agreement, stiff legs continue to be employed to model walking. Here, we show that leg compliance is necessary to model walking and, in the process, identify the principles that underpin two important features of legged locomotion: First, at the same speed, step length, and stance duration, multiple gaits that differ in the number of leg contraction cycles are possible. Among them, humans and other animals choose a gait with M-shaped vertical ground reaction forces because it is energetically favored. Second, the transition from walking to running occurs because of the inability to redirect the vertical component of the velocity during the double stance phase. Additionally, we also examine the limits of double spring-loaded pendulum (DSLIP) as a quantitative model for locomotion, and conclude that DSLIP is limited as a model for walking. However, insights gleaned from the analytical treatment of DSLIP are general and will inform the construction of more accurate models of walking.

Temporal integration in human auditory cortex is predominantly yoked to absolute time, not structure duration
Sound structures such as phonemes and words have highly variable durations. Thus, there is a fundamental difference between integrating across absolute time (e.g., 100 ms) vs. sound structure (e.g., phonemes). Auditory and cognitive models have traditionally cast neural integration in terms of time and structure, respectively, but the extent to which cortical computations reflect time or structure remains unknown. To answer this question, we rescaled the duration of all speech structures using time stretching/compression and measured integration windows in the human auditory cortex using a new experimental/computational method applied to spatiotemporally precise intracranial recordings. We observed significantly longer integration windows for stretched speech, but this lengthening was very small (~5%) relative to the change in structure durations, even in non-primary regions strongly implicated in speech-specific processing. These findings demonstrate that time-yoked computations dominate throughout the human auditory cortex, placing important constraints on neurocomputational models of structure processing.

The electrogenicity of the Na+/K+-ATPase poses challenges for computation in highly active spiking cells
The evolution of the Na+/K+-ATPase laid the foundation for ion homeostasis and electrical signalling. While not required for restoration of ionic gradients, the electrogenicity of the pump (resulting from its 3:2 stoichiometry) is useful to prevent runaway activity. As we show here, electrogenicity also comes with disadvantageous side effects: (1) an activity-dependent shift in a cell's baseline firing and (2) interference with computation, disturbing network entrainment when inputs change strongly. We exemplify these generic effects in a mathematical model of the weakly electric fish electrocyte, which spikes at hundreds of Hz and is exposed to abrupt rate changes when producing behaviourally relevant communication signals. We discuss biophysical strategies allowing cells to mitigate the consequences of electrogenicity at additional metabolic cost and postulate an interesting role for a voltage dependence of the Na+/K+-ATPase. Our work shows that the pump's electrogenicity opens an additional axis of vulnerability that is likely to play a role in brain disease.

Cardiac responses to auditory irregularities reveal hierarchical information processing during sleep
Our ability to process environmental stimuli varies during sleep. Although much research focused on neural processing, emerging evidence shows that bodily signals may play a key role in understanding high-level sensory processing during sleep. Here, we tested how cardiac responses to the local-global paradigm, a typical oddball task probing the processing of simple (local) and complex (global) sensory irregularities. To do so, we analyzed electrocardiography (ECG) signals in a total of 56 participants from two existing datasets which contained cerebral responses to local auditory irregularities, but which did not analyze the ECG data before. We found that cardiac activity slowed down after global, but not local, auditory irregularities, revealing the presence of global deviance effect in Rapid Eye Movement (REM) sleep. In contrast, cardiac activity was faster after local, but not global, deviants in Non-Rapid Eye Movement (NREM) sleep. Overall, our results demonstrate that cardiac responses to auditory irregularities inform about hierarchical information processing and its variations during sleep beyond cerebral activity. They highlight the embodiment of cognitive function and the value of cardiac signals to understand the variations of sensory processing during sleep.

microRNA-138-5p suppresses excitatory synaptic strength at the cerebellar input layer
MicroRNAs are small, highly conserved non-coding RNAs that negatively regulate mRNA translation and stability. In the brain, microRNAs contribute to neuronal development, synaptogenesis, and synaptic plasticity. The microRNA 138-5p (miR-138-5p) controls inhibitory synaptic transmission in the hippocampus and is highly expressed in cerebellar excitatory neurons. However, its role in cerebellar synaptic transmission remains unkwown. Here, we investigated excitatory transmission within the cerebellum in mice expressing a sponge construct that sequesters endogenous miR-138-5p. Mossy fiber stimulation-evoked excitatory postsynaptic currents (EPSCs) in granule cells were significantly larger compared with controls. Furthermore, we observed larger miniature EPSC amplitudes, suggesting increased postsynaptic AMPA receptor numbers. High-frequency train stimulations revealed enhanced short-term depression following miR-138-5p downregulation. Together with computational modelling, this suggests a negative regulation of presynaptic release probability. Overall, our results demonstrate that miR-138-5p suppresses synaptic strength through pre- and postsynaptic mechanisms, providing a powerful mechanism for tuning excitatory synaptic input into the cerebellum.