bioRxiv Subject Collection: Neuroscience's Journal

Understanding the development of neural abnormalities in adolescents with mental health problems: a longitudinal study
Many mental health problems are neurodevelopmental in nature and have an onset during childhood. Mental health disorders are associated with neural abnormalities, but it is unclear when those emerge and how this relates to the development of different mental health problems. We used data from the largest longitudinal neurodevelopmental study to identify the structural and functional brain changes that co-occur with the onset of six mental health problems. The results showed premorbid brain-wide abnormalities that were comparable between internalizing and different from externalizing problems, and differential neurodevelopmental trajectories for specific brain regions in 11- to 12-year-old adolescents who developed ADHD, conduct, depressive and oppositional defiant problems. These results reveal that the onset of different mental health problems co-occur with common as well as problem-specific brain abnormalities.

The representational nature of spatio-temporal recurrent processing in visual object recognition
The human brain orchestrates object vision through an interplay of feedforward processing in concert with recurrent processing. However, where, when and how recurrent processing contributes to visual processing is incompletely understood due to the difficulties in teasing apart feedforward and recurrent processing. We combined a backward masking paradigm with multivariate analysis on EEG and fMRI data to isolate and characterize the nature of recurrent processing. We find that recurrent processing substantially shapes visual representations across the ventral visual stream, starting early on at around 100ms in early visual cortex (EVC) and in two later phases of around 175 and 300ms in lateral occipital cortex (LOC), adding persistent rather than transient neural dynamics to visual processing. Using deep neural network models for comparison with the brain, we show that recurrence changes the feature format in LOC from predominantly mid-level to more high-level features. Finally, we show that recurrence is mediated by four distinct spectro-temporal neural components in EVC and LOC, which span the theta to beta frequency range. Together, our results reveal the nature and mechanisms of the effects of recurrent processing on the visual representations in the human brain.

Healthy aging delays and dedifferentiates high-level visual representations
Healthy aging impacts visual information processing with consequences for subsequent high-level cognition and everyday behavior, but the underlying neural changes in visual representations remain unknown. Here, we investigate the nature of representations underlying object recognition in older compared to younger adults by tracking them in time using EEG, across space using fMRI, and by probing their behavioral relevance using similarity judgements. Applying a multivariate analysis framework to combine experimental assessments, four key findings about how brain aging impacts object recognition emerge. First, aging selectively delays the formation of object representations, profoundly changing the chronometry of visual processing. Second, the delay in the formation of object representations emerges in high-level rather than low- and mid-level ventral visual cortex, supporting the theory that brain areas developing last deteriorate first. Third, aging reduces content selectivity in high-level ventral visual cortex, indicating age-related neural dedifferentiation as the mechanism of representational change. Finally, we demonstrate that the identified representations of the aging brain are behaviorally relevant, ascertaining ecological relevance. Together, our results reveal the impact of healthy aging on the visual brain.

Interaural level difference sensitivity in neonatally deafened rats fitted with bilateral cochlear implants
Bilateral cochlear implant (CI) patients exhibit significant limitations in spatial hearing. Their ability to process interaural time differences (ITDs) is often impaired, while their ability to process interaural level differences (ILDs) remains comparatively good. Clinical studies aiming to identify the causes of these limitations are often plagued by confounds and ethical limitations. Recent behavioral work suggests that rats may be a good animal model for studying binaural hearing under neuroprosthetic stimulation, as rats develop excellent ITD sensitivity when provided with suitable CI stimulation. However, their ability to use ILDs has not yet been characterized. Objective of this study is to address this knowledge gap. Neontally deafened rats were bilaterally fitted with CIs, and trained to lateralize binaural stimuli according to ILD. Their behavioral ILD thresholds were measured at pulse rates from 50 to 2400 pps. CI rats exhibited high sensitivity to ILDs with thresholds of a few dB at all tested pulse rates. We conclude that early deafened rats develop good sensitivity, not only to ITDs but also to ILDs, if provided with appropriate CI stimulation. Their generally good performance, in line with expectations from other mammalian species, validates rats as an excellent model for research on binaural auditory prostheses.

MIND WANDERING DURING IMPLICIT LEARNING IS ASSOCIATED WITH INCREASED PERIODIC EEG ACTIVITY AND IMPROVED EXTRACTION OF HIDDEN PROBABILISTIC PATTERNS
Mind wandering, occupying 30-50% of our waking time, remains an enigmatic phenomenon in cognitive neuroscience. Predominantly viewed negatively, mind wandering is often associated with detrimental impacts on attention-demanding (model-based) tasks in both natural settings and laboratory conditions. Mind wandering however, might not be detrimental for all cognitive domains. We proposed that mind wandering may facilitate model-free processes, such as probabilistic learning, which relies on the automatic acquisition of statistical regularities with minimal attentional demands. We administered a well-established implicit probabilistic learning task combined with mind wandering thought probes in healthy adults (N = 37, 30 females). To explore the neural correlates of mind wandering and probabilistic learning, participants were fitted with high-density electroencephalography. Our findings indicate that probabilistic learning was not only immune to periods of mind wandering, but was positively associated with it. Spontaneous, as opposed to deliberate mind wandering, was particularly beneficial for extracting the probabilistic patterns hidden in the visual stream. Additionally, cortical oscillatory activity in the low-frequency (slow and delta) range, indicative of covert sleep-like states, was associated with both mind wandering and improved probabilistic learning, particularly in the early stages of the task. Given the importance of probabilistic implicit learning in predictive processing, our findings provide novel insights into the potential cognitive benefits of task-unrelated thoughts in addition to shedding light on its neural mechanisms. This surprising benefit challenges the predominant view of mind wandering as solely detrimental and highlights its complex role in human cognition, especially in memory consolidation.

Hypersynchronous iPSC-derived SHANK2 neuronal networks are rescued by mGluR5 agonism
Variants in the gene encoding the postsynaptic scaffolding protein SHANK2 are associated with several neurodevelopmental disorders, including autism spectrum disorder. Here, we used in vitro multielectrode arrays and pharmacological manipulations to characterize how functional connectivity and network-level firing properties were altered in cultures of human iPSC-derived SHANK2 neurons. Using two isogenic pairs of SHANK2 cell lines, we showed that the SHANK2 hyperconnectivity phenotype was recapitulated at the network level. SHANK2 networks displayed significantly increased frequency and reduced duration of network burst events relative to controls. SHANK2 network activity was hypersynchronous, with increased functional correlation strength between recording channels. Analysis of intra-network burst firing dynamics revealed that spikes within SHANK2 network bursts were organized into high-frequency trains, producing a distinctive network burst shape. Calcium-dependent events called reverberating super bursts (RSBs) were observed in control networks but rarely occurred in SHANK2 networks. SHANK2 network hypersynchrony and numbers of strong correlations were fully rescued by the group 1 mGluR agonist DHPG, that also restored detection of RSBs and significantly improved network burst frequency and duration metrics. Our results demonstrate that SHANK2 variants produce a functional hyperconnectivity phenotype that deviates from the developmental trajectory of isogenic control networks. Furthermore, the hypersynchronous phenotype was rescued by pharmacologically regulating glutamatergic neurotransmission.

MRI signatures of cortical microstructure in human development align with oligodendrocyte cell-type expression
Neuroanatomical changes to the cortex during adolescence have been well documented using MRI, revealing ongoing cortical thinning and volume loss with age. However, the underlying cellular mechanisms remain elusive with conventional neuroimaging. Recent advances in MRI hardware and new biophysical models of tissue informed by diffusion MRI data hold promise for identifying the cellular changes driving these morphological observations. This study used ultra-strong gradient MRI to obtain high-resolution, in vivo estimates of cortical neurite and soma microstructure in sample of typically developing children and adolescents. Cortical neurite signal fraction, attributed to neuronal and glial processes, increased with age (mean R2fneurite=.53, p<3.3e-11, 11.91% increase over age), while apparent soma radius decreased (mean R2Rsoma=.48, p<4.4e-10, 1% decrease over age) across domain-specific networks. To complement these findings, developmental patterns of cortical gene expression in two independent post-mortem databases were analysed. This revealed increased expression of genes expressed in oligodendrocytes, and excitatory neurons, alongside a relative decrease in expression of genes expressed in astrocyte, microglia and endothelial cell-types. Age-related genes were significantly enriched in cortical oligodendrocytes, oligodendrocyte progenitors and Layer 5-6 neurons (pFDR<.001) and prominently expressed in adolescence and young adulthood. The spatial and temporal alignment of oligodendrocyte cell-type gene expression with neurite and soma microstructural changes suggest that ongoing cortical myelination processes contribute to adolescent cortical development. These findings highlight the role of intra-cortical myelination in cortical maturation during adolescence and into adulthood.

Event boundaries drive norepinephrine release and distinctive neural representations of space in the rodent hippocampus
Episodic memories are temporally segmented around event boundaries that tend to coincide with moments of environmental change. During these times, the state of the brain should change rapidly, or reset, to ensure that the information encountered before and after an event boundary is encoded in different neuronal populations. Norepinephrine (NE) is thought to facilitate this network reorganization. However, it is unknown whether event boundaries drive NE release in the hippocampus and, if so, how NE release relates to changes in hippocampal firing patterns. The advent of the new GRABNE sensor now allows for the measurement of NE binding with sub-second resolution. Using this tool in mice, we tested whether NE is released into the dorsal hippocampus during event boundaries defined by unexpected transitions between spatial contexts and presentations of novel objections. We found that NE binding dynamics were well explained by the time elapsed after each of these environmental changes, and were not related to conditioned behaviors, exploratory bouts of movement, or reward. Familiarity with a spatial context accelerated the rate in which phasic NE binding decayed to baseline. Knowing when NE is elevated, we tested how hippocampal coding of space differs during these moments. Immediately after context transitions we observed relatively unique patterns of neural spiking which settled into a modal state at a similar rate in which NE returned to baseline. These results are consistent with a model wherein NE release drives hippocampal representations away from a steady-state attractor. We hypothesize that the distinctive neural codes observed after each event boundary may facilitate long-term memory and contribute to the neural basis for the primacy effect.

An intrinsic hierarchical, retinotopic organization of pulvinar connectivity in the human neonate
Thalamic connectivity is crucial for the development of the neocortex. The pulvinar nuclei are thought to be particularly important for visual development due to their involvement in various functions that emerge early in infancy. The development of these connections constrains the role the pulvinar plays in infant visual processing and the maturation of associated cortical networks. However, the extent to which pulvino-cortical pathways found in adults are established at birth remains largely unknown, limiting our understanding of how these thalamic connections may support infant vision. To address this gap, we examined the organization of pulvino-cortical connections in human neonates using probabilistic tractography analyses on diffusion imaging data. Our findings revealed the presence of white matter pathways between the pulvinar and each individual visual area at birth. These pathways exhibited specificity in their connectivity within the pulvinar, reflecting both intraareal retinotopic organization and the hierarchical organization across ventral, lateral, and dorsal visual cortical pathways. These connections could enable detailed processing of information across sensory space and communication along distinct processing pathways. Comparative analyses revealed that the large-scale organization of pulvino-cortical connectivity in neonates mirrored that of adults. However, connectivity with ventral visual cortex was less adult-like than the other cortical pathways, aligning with prior findings of protracted development associated with the visual recognition pathway. These results deepen our understanding of the developmental trajectory of thalamocortical connections and provide a framework for how subcortical may support early perceptual abilities and scaffold the development of cortex.

Unique longitudinal contributions of sulcal interruptions to reading acquisition in children
A growing body of literature indicates strong associations between indentations of the cerebral cortex (i.e., sulci) and individual differences in cognitive performance. Interruptions, or gaps, of sulci (historically known as pli de passage) are particularly intriguing as previous work suggests that these interruptions have a causal effect on cognitive development. Here, we tested how the presence and morphology of sulcal interruptions in the left posterior occipitotemporal sulcus (pOTS) longitudinally impact the development of a culturally-acquired skill: reading. Forty-three children were successfully followed from age 5 in kindergarten, at the onset of literacy instruction, to ages 7 and 8 with assessments of cognitive, pre-literacy, and literacy skills, as well as MRI anatomical scans at ages 5 and 8. Crucially, we demonstrate that the presence of a left pOTS gap at 5 years is a specific and robust longitudinal predictor of better future reading skills in children, with large observed benefits on reading behavior ranging from letter knowledge to reading comprehension. The effect of left pOTS interruptions on reading acquisition accumulated through time, and was larger than the impact of benchmark cognitive and familial predictors of reading ability and disability. Finally, we show that increased local U-fiber white matter connectivity associated with such sulcal interruptions possibly underlie these behavioral benefits, by providing a computational advantage. To our knowledge, this is the first quantitative evidence supporting a potential integrative gray-white matter mechanism underlying the cognitive benefits of macro-anatomical differences in sulcal morphology related to longitudinal improvements in a culturally-acquired skill.

The big tau splice isoform resists Alzheimer's-related pathological changes
In Alzheimer's disease (AD), the microtubule-binding protein tau becomes abnormally hyperphosphorylated and aggregated in selective brain regions such as the cortex and hippocampus. However, other brain regions like the cerebellum and brain stem remain largely intact despite the universal expression of tau throughout the brain. Here, we found that an understudied splice isoform of tau termed "big tau" is significantly more abundant in the brain regions less vulnerable to tau pathology compared to tau pathology-vulnerable regions. We used various cellular and animal models to demonstrate that big tau possesses multiple properties that can resist AD-related pathological changes. Importantly, human AD patients show a higher expression level of pathology-resisting big tau in the cerebellum, the brain region spared from tau pathology. Our study examines the unique properties of big tau, expanding our current understanding of tau pathophysiology. Altogether, our data suggest that alternative splicing to favor big tau is a viable strategy to modulate tau pathology.

A computational model of altered neuronal activity in altered gravity
Electrophysiological experiments have shown that neuronal activity changes upon exposure to altered gravity. More specifically, the firing rate increases during microgravity and decreases during centrifugal-induced hypergravity. However, the mechanism by which altered gravity impacts neuronal activity is still unknown. Different explanations have been proposed: a first hypothesis states that microgravity increases the fluidity of the cell membrane and modifies the properties of the neurons' ion channels. Another hypothesis suggests the role of mechano-gated (MG) ion channels depolarizing the cells during microgravity exposure. Although intuitive, these models have not been backed by quantitative analyses nor simulations. Here, we developed computational models of the impact of altered gravity, both on single cell activity and on population dynamics. Firstly, in line with previous electrophysiological experiments, we suggest that microgravity could be modelled as an increase of the voltage-dependent channel transition rates, which are assumed to be the result of higher membrane fluidity and can be readily implemented into the Hodgkin-Huxley model. Using in-silico simulations of single neurons, we show that this model of the influence of gravity on neuronal activity allows to reproduce the increased firing and burst rates observed in microgravity. Secondly, we explore the role of MG ion channels on population activity. We show that recordings can be fitted by a network of connected excitatory neurons, whose activity is balanced by firing rate adaptation. Adding a small depolarizing current to account for the activation of mechano-gated channels also reproduces the observed increased firing and burst rates. Overall, our results fill an important gap in the literature, by providing a computational link between altered gravity and neuronal activity.

Enhancer AAVs for targeting spinal motor neurons and descending motor pathways in rodents and macaque
Experimental access to cell types within the mammalian spinal cord is severely limited by the availability of genetic tools. To enable access to lower motor neurons (LMNs) and LMN subtypes, which function to integrate information from the brain and control movement through direct innervation of effector muscles, we generated single cell multiome datasets from mouse and macaque spinal cords and discovered putative enhancers for each neuronal population. We cloned these enhancers into adeno-associated viral vectors (AAVs) driving a reporter fluorophore and functionally screened them in mouse. The most promising candidate enhancers were then extensively characterized using imaging and molecular techniques and further tested in rat and macaque to show conservation of LMN labeling. Additionally, we combined enhancer elements into a single vector to achieve simultaneous labeling of upper motor neurons (UMNs) and LMNs. This unprecedented LMN toolkit will enable future investigations of cell type function across species and potential therapeutic interventions for human neurodegenerative diseases.

Senescent cell clearance ameliorates temporal lobe epilepsy and associated spatial memory deficits in mice
Current therapies for the epilepsies only treat the symptoms, but do not prevent epileptogenesis (the process in which epilepsy develops). Many cellular responses during epileptogenesis are also common hallmarks of cellular senescence, which halts proliferation of damaged cells. Clearing senescent cells (SCs) restores function in several age-associated and neurodegenerative disease models. It is unknown whether SC accumulation contributes to epileptogenesis and associated cognitive impairments. To address this question, we used a mouse model of temporal lobe epilepsy (TLE) and characterized the senescence phenotype throughout epileptogenesis. SCs accumulated 2 weeks after SE and were predominantly microglia. We ablated SCs and reduced (and in some cases prevented) the emergence of spontaneous seizures and normalized cognitive function in mice. Suggesting that this is a translationally-relevant target we also found SC accumulation in resected hippocampi from patients with TLE. These findings indicate that SC ablation after an epileptogenic insult is a potential anti-epileptogenic therapy.

Cortical Acetylcholine Response to Deep Brain Stimulation of the Basal Forebrain
Background: Deep brain stimulation (DBS), the direct electrical stimulation of neuronal tissue in the basal forebrain to enhance release of the neurotransmitter acetylcholine, is under consideration as a method to improve executive function in patients with dementia. While some small studies indicate a positive response in the clinical setting, the relationship between DBS and acetylcholine pharmacokinetics is incompletely understood. Objective: We examined the cortical acetylcholine response to different stimulation parameters of the basal forebrain. Methods: 2-photon imaging was combined with deep brain stimulation. Stimulating electrodes were implanted in the subpallidal basal forebrain, and the ipsilateral somatosensory cortex was imaged. Acetylcholine activity was determined using the GRABACh-3.0 muscarinic acetylcholine receptor sensor, and blood vessels were imaged with Texas red. Results: Experiments manipulating pulse train frequency demonstrated that integrated acetylcholine induced fluorescence was insensitive to frequency, and that peak levels were achieved with frequencies from 60 to 130 Hz. Altering pulse train length indicated that longer stimulation resulted in higher peaks and more activation with sublinear summation. The acetylcholinesterase inhibitor donepezil increased the peak response to 10s of stimulation at 60Hz, and the integrated response increased 57% with the 2 mg/kg dose, and 126% with the 4 mg/kg dose. Acetylcholine levels returned to baseline with a time constant of 14 to 18 seconds in all experiments. Conclusions: These data demonstrate that acetylcholine receptor activation is insensitive to frequency between 60 and 130 Hz. High peak responses are achieved with up to 900 pulses. Donepezil increases total acetylcholine receptor activation associated with DBS but did not change temporal kinetics. The long time constants observed in the cerebral cortex add to the evidence supporting volume in addition to synaptic transmission.

Sleep homeostasis in lizards and the role of cortex
Although their phenotypes are diverse, slow-wave sleep (SWS) and rapid eye movement sleep (REMS) are the two primary components of electrophysiological sleep (e-sleep) in mammals and birds. Slow waves in the cortex not only characterize SWS but are also used as biological markers for sleep homeostasis, given their rebound after sleep deprivation (SD). Recently, it has been reported that the Australian dragon Pogona vitticeps exhibits two-stage sleep pattern in the dorsal ventricular ridge (DVR), which includes a homologue of the mammalian claustrum (CLA). It remains unclear whether reptilian e-sleep, which has been characterized by activity outside the cortex, compensates for sleep loss, as observed in mammals. We here report a significant rebound in the local field potential (LFP) after 7 hours of SD, during both SWS and REMS. Meanwhile, the cycle and mean bout length of SWS/REMS remained unaffected. We further investigated a possible role of the cortex in e-sleep regulation and homeostasis in Pogona and found that, although a corticotomy had no obvious effect on the LFP features investigated, it abolished LFP power rebound in the CLA/DVR after SD. These findings suggest that e-sleep homeostasis is a common feature in amniotes, and that cortex is involved in regulating activity rebounds in reptiles and mammals.

Effects of unconscious tactile stimuli on autonomic nervous activity and afferent signal processing
Autonomic nervous system (ANS) is a mechanism that regulates our internal environment. In recent years, the interest in how tactile stimuli presented directly to the body affect ANS function and cortical processing in humans has been renewed. However, it is not yet clear how subtle tactile stimuli below the level of consciousness affect human heart rate and cortical processing. To examine this, subthreshold electrical stimuli were presented to the left forearm of 43 participants during an image-viewing task, and electrocardiogram (ECG) and electroencephalogram (EEG) data were collected. The changes in the R-wave interval of the ECG immediately after the subthreshold electrical presentation and heartbeat-evoked potential (HEP), the afferent signal processing of cardiac activity, were measured. The results showed that heart rate decelerated immediately after the presentation of subthreshold electrical stimuli. The HEP during stimulus presentation was amplified for participants with greater heart rate acceleration immediately after this deceleration. The magnitude of these effects depended on the type of the subthreshold tactile stimuli. The results suggest that even with subthreshold stimulation, the changes in autonomic activity associated with orienting response and related afferent signal processing differ depending on the clarity of the tactile stimuli.

Event-marked Windowed Communication: Inferring activity propagation from neural time series
Tracking signal propagation in nervous systems is crucial to our understanding of brain function and information processing. Current methods for inferring neural communication track patterns of sustained co-activation over time, making them unsuitable to detect discrete instances of signal transmission. Here, we propose Event-marked Windowed Communication (EWC), a new analytical framework to infer functional interactions arising from discrete signalling events between neural elements, in otherwise continuous time series data. In contrast to conventional measures of functional connectivity, our method utilises an event-based subsampling of neural time series, which allows it to capture the statistical analogue of activity propagation. We test EWC on simulations of neural dynamics and show that it is capable of retrieving ground truth motifs of directional signalling, over a range of model configurations. Critically, we demonstrate that EWC's subsampling approach affords profound reductions in computation times, compared to established network inference methods such as transfer entropy. Lastly, we showcase the utility of EWC to infer whole-brain functional networks from MEG recordings. Networks computed using EWC and transfer entropy were highly correlated (median r=0.821 across subjects), but EWC inference was approximately 6.5 times faster per epoch. In summary, our work presents a new method to infer signalling from time series of neural activity at low computational costs. Our framework is flexible and can be applied to activity time series captured by diverse functional neuroimaging modalities, opening up new avenues for the study of neural communication.

Subjective salience ratings are a reliable proxy for physiological measures of arousal
Pain is an inherently salient multidimensional experience that warns us of bodily threat and promotes escape behaviours. Stimuli of any sensory modalities can be salient depending on stimulus features and context. This poses a challenge in delineating pain-specific processes in the brain, rather than salience-driven activity. It is thus essential to salience match control (innocuous) stimuli and noxious stimuli, in order to remove salience effects, and identify pain-specific activity. Previous studies have salience-matched either through subjective salience ratings or the skin conductance response (SCR), the latter of which serves as a physiological measure of arousal. Though an objective measure that overcomes the nebulous construct of salience, SCR cannot be used to salience-match in real-time (i.e., during an experiment) and assumes an association between salience and physiological arousal elicited by painful and non-painful stimuli, but this has not been explicitly tested. To determine whether salience and physiological arousal are associated, sixteen healthy adults experienced 30 heat pain and 30 non-painful electric stimuli of varying intensities. Stimuli were subjectively matched for salience and physiologically matched for arousal using SCR. A linear mixed model found no differences in SCR between salience-matched heat and electric stimuli. A mediation analysis showed that salience fully mediated the relationship between stimulus intensity and SCR (proportion mediated=84%). In conclusion, salience and physiological arousal are associated, and subjective salience ratings are a suitable for salience-matching pain with non-painful stimuli. Future work can thus use subjective salience ratings to delineate pain-specific processes.

CIB2 function is distinct from Whirlin in the development of cochlear stereocilia staircase pattern
Variations in genes coding for calcium and integrin binding protein 2 (CIB2) and whirlin cause deafness both in humans and mice. We previously reported that CIB2 binds to whirlin, and is essential for normal staircase architecture of auditory hair cells stereocilia. Here, we refine the interacting domains between these proteins and provide evidence that both proteins have distinct role in the development and organization of stereocilia bundles required for auditory transduction. Using a series of CIB2 and whirlin deletion constructs and nanoscale pulldown (NanoSPD) assays, we localized the regions of CIB2 that are critical for interaction with whirlin. AlphaFold 2 multimer, independently identified the same interacting regions between CIB2 and whirlin proteins, providing a detailed structural model of the interaction between the CIB2 EF2 domain and whirlin HHD2 domain. Next, we investigated genetic interaction between murine Cib2 and Whrn using genetic approaches. Hearing in mice double heterozygous for functionally null alleles (Cib2KO/+;Whrnwi/+) was similar to age-matched wild type mice, indicating that partial deficiency for both Cib2 and Whrn does not impair hearing. Double homozygous mutant mice (Cib2KO/KO;Whrnwi/wi) had profound hearing loss and cochlear stereocilia exhibited a predominant phenotype seen in single Whrnwi/wi mutants. Furthermore, over-expression of Whrn in Cib2KO/KO mice did not rescue the stereocilia morphology. These data suggest that, CIB2 is multifunctional, with key independent functions in development and/or maintenance of stereocilia staircase pattern in auditory hair cells.

Spreading depolarizations exhaust neuronal ATP in a model of cerebral ischemia
Spreading depolarizations (SDs) have been identified in various brain pathologies. SDs increase the cerebral energy demand and, concomitantly, oxygen consumption, which indicates enhanced synthesis of adenosine triphosphate (ATP) by oxidative phosphorylation. Therefore, SDs are considered particularly detrimental during reduced supply of oxygen and glucose. However, measurements of intracellular neuronal ATP ([ATP]i), ultimately reporting the balance of ATP synthesis and consumption during SDs, have not yet been conducted. In this study, we investigated neuronal ATP homeostasis during SDs using 2-photon imaging in acute brain slices from adult mice, expressing the ATP sensor ATeam1.03YEMK in neurons. SDs were induced by application of potassium chloride or by oxygen and glucose deprivation (OGD) and were detected by recording the local field potential, extracellular potassium, as well as the intrinsic optical signal. We found that, in the presence of oxygen and glucose, SDs were accompanied by a substantial but transient drop in neuronal [ATP]i. OGD, which prior to SD was accompanied by a slight reduction in [ATP]i only, led to an even larger, terminal drop in [ATP]i during SDs. Subsequently, we investigated whether neurons could still regenerate ATP if oxygen and glucose were promptly resupplied following SD detection. The data show that ATP depletion was essentially reversible in most cells. Our findings indicate that SDs are accompanied by a substantial increase in ATP consumption beyond production. This, under conditions that mimic reduced blood supply, leads to a breakdown of [ATP]i. Therefore, our findings support therapeutic strategies targeting SDs after cerebral ischemia.

Opioid-Induced Inter-regional Dysconnectivity Correlates with Analgesia in Awake Mouse Brains
The mu-opioid receptor (MOP) is crucial for both the therapeutic and addictive effects of opioids. Using a multimodal experimental approach, here we combined awake functional ultrasound (fUS) imaging with behavioral and molecular assessments, to examine opioid-induced changes in brain activation and functional connectivity (FC). Morphine, fentanyl, and methadone induce significant dose- and time-dependent reorganization of brain perfusion, oscillations and FC in awake mice. Notably, opioids induce a transient, region-specific hyperperfusion, followed by a consistent MOP-specific dysconnectivity marked by decreased FC of the somatosensory cortex to hippocampal and thalamic regions, alongside increased subcortical and intra-cortical FC. These FC changes temporally correlate with generalized brain MOP activation and analgesia, but not with hypermobility and respiratory depression, suggesting a reorganization of inter-regional FC as a key opioid effect.

Dynamic network features of functional and structural brain networks support visual working memory in aging adults
In this work, we investigated the relationship between structural connectivity and the dynamics of functional connectivity and how this relationship changes with age to benefit cognitive functions. Visual working memory (VWM) is an important brain function that allows us to maintain a mental representation of the world around us, but its capacity and precision peaks by around 20 years old and decreases steadily throughout the rest of our lives. This research examined the functional brain network dynamics associated with VWM throughout the lifespan and found that Default Mode Network and Fronto-Parietal Network states were more well represented in individuals with better VWM. Furthermore, transitions between the Visual/Somatomotor Network state and the Attention Network state were more well-represented in older adults, and a network control theory simulation demonstrated that structural connectivity differences supporting this transition were associated with better VWM, especially in middle-aged individuals. The structural connectivity of regions from all states was important for supporting this transition in younger adults, while regions within the Visual/Somatomotor and Attention Network states were more important in older adults. These findings demonstrate that structural connectivity supports flexible, functional dynamics that allow for better VWM with age and may lead to important interventions to uphold healthy VWM throughout the lifespan.

It's the Sound not the Pulse: Peripheral Magnetic Stimulation Reduces Central Sensitization through Auditory Modulatory Effects
Repetitive peripheral magnetic stimulation (rPMS) is a non-pharmacological, non-invasive analgesic modality with limited side effects. However, there is a paucity of controlled studies demonstrating its efficacy compared to existing pain management tools. Here, in an initial sample of 100 healthy participants (age 18-40), we compared the analgesic efficacy of two rPMS stimulation protocols--continuous theta burst stimulation (ctbPMS) and intermittent TBS (itbPMS)--against transcutaneous electric nerve stimulation (TENS), a peripheral stimulation technique that is commonly used for pain management. We also included a sham rPMS protocol where participants heard the sound of rPMS stimulation while the coil was placed over their arm, but received no peripheral stimulation. We hypothesized that itbPMS and ctbPMS--but not sham--would reduce pain intensity, pain unpleasantness, and secondary hyperalgesia evoked by a phasic heat pain (PHP) paradigm on the volar forearm with similar efficacy to TENS. Neither rPMS nor TENS reduced reported pain intensity or unpleasantness (p>0.25). However, ctbPMS and itbPMS significantly reduced the area of secondary hyperalgesia, whereas TENS did not (F3,96= 4.828, p= 0.004). Unexpectedly, sham rPMS, which involved auditory but no peripheral nerve stimulation, also significantly reduced secondary hyperalgesia compared to TENS. We performed a second study (n=32) to investigate auditory contributions to rPMS analgesia. Masking the rPMS stimulation sound with pink noise eliminated its analgesic effect on secondary hyperalgesia (p=0.5). This is the first study to show that the analgesic properties of rPMS in acute experimental pain may be largely attributed to its auditory component rather than peripheral nerve stimulation.

Muscarinic receptor activation preferentially inhibits rebound in vulnerable dopaminergic neurons
Dopaminergic subpopulations of the substantia nigra pars compacta (SNc) differentially degenerate in Parkinson's disease and are characterized by unique electrophysiological properties. The vulnerable population expresses a T-type calcium channel-mediated afterdepolarization (ADP) and shows rebound activity upon release from inhibition, whereas the resilient population does not have an ADP and is slower to fire after hyperpolarization. This rebound activity can trigger dopamine release in the striatum, an important component of basal ganglia function. Using whole-cell patch clamp electrophysiology on ex vivo slices from adult mice of both sexes, we find that muscarinic activation with the non-selective muscarinic agonist Oxotremorine inhibits rebound activity more strongly in vulnerable vs resilient SNc neurons. Here, we show that this effect depends on the direct activation of muscarinic receptors on the SNc dopaminergic neurons. Through a series of pharmacological and transgenic knock-out experiments, we tested whether the muscarinic inhibition of rebound was mediated through the canonical rebound-related ion channels: T-type calcium channels, hyperpolarization-activated cation channels (HCN), and A-type potassium channels. We find that muscarinic receptor activation inhibits HCN-mediated current (Ih) in vulnerable SNc neurons, but that Ih activity is not necessary for the muscarinic inhibition of rebound activity. Similarly, we find that Oxotremorine inhibits rebound activity independently of T-type calcium channels and A-type potassium channels. Together these findings reveal new principles governing acetylcholine and dopamine interactions, showing that muscarinic receptors directly affect SNc rebound activity in the midbrain at the somatodendritic level and differentially modify information processing in distinct SNc subpopulations.

Capillary connections between sensory circumventricular organs and adjacent parenchyma enable local volume transmission
Among contributors to diffusible signaling are portal systems which join two capillary beds through connecting veins (Dorland 2020). Portal systems allow diffusible signals to be transported in high concentrations directly from one capillary bed to the other without dilution in the systemic circulation. Two portal systems have been identified in the brain. The first was discovered almost a century ago and connects the median eminence to the anterior pituitary gland (Popa & Fielding 1930). The second was discovered a few years ago, and links the suprachiasmatic nucleus to the organum vasculosum of the lamina terminalis, a sensory circumventricular organ (CVO) (Yao et al. 2021). Sensory CVOs bear neuronal receptors for sensing signals in the fluid milieu (McKinley et al. 2003). They line the surface of brain ventricles and bear fenestrated capillaries, thereby lacking blood brain barriers. It is not known whether the other sensory CVOs, namely the subfornical organ (SFO), and area postrema (AP) form portal neurovascular connections with nearby parenchymal tissue. This has been difficult to establish as the structures lie at the midline and protrude into the ventricular space. To preserve the integrity of the vasculature of CVOs and their adjacent neuropil, we combined iDISCO clearing and light-sheet microscopy to acquire volumetric images of blood vessels. The results indicate that there is a portal pathway linking the capillary vessels of the SFO and the posterior septal nuclei, namely the septofimbrial nucleus and the triangular nucleus of the septum. Unlike the latter arrangement, the AP and the nucleus of the solitary tract share their capillary beds. Taken together, the results reveal that all three sensory circumventricular organs bear specialized capillary connections to adjacent neuropil, providing a direct route for diffusible signals to travel from their source to their targets.

Unsupervised learning as a computational principle works in visual learning of natural scenes, but not of artificial stimuli
The question of whether we learn exposed visual features remains a subject of controversy. A prevalent computational model suggests that visual features frequently exposed to observers in natural environments are likely to be learned. However, this unsupervised learning model appears to be contradicted by the significant body of experimental results with human participants that indicates visual perceptual learning (VPL) of visible task-irrelevant features does not occur with frequent exposure. Here, we demonstrate a resolution to this controversy with a new finding: Exposure to a dominant global orientation as task-irrelevant leads to VPL of the orientation, particularly when the orientation is derived from natural scene images, whereas VPL did not occur with artificial images even with matched distributions of local orientations and spatial frequencies to natural scene images. Further investigation revealed that this disparity arises from the presence of higher-order statistics derived from natural scene images: global structures such as correlations between different local orientation and spatial frequency channels. Moreover, behavioral and neuroimaging results indicate that the dominant orientation from these higher-order statistics undergoes less attentional suppression than that from artificial images, which may facilitate VPL. Our results contribute to resolving the controversy by affirming the validity of unsupervised learning models for natural scenes but not for artificial stimuli. They challenge the assumption that VPL occurring in everyday life can be predicted by laws governing VPL for conventionally used artificial stimuli.

Visual Congruency Modulates Music Reward through Sensorimotor Integration
There is emerging evidence that a performer's body movements may enhance the music-induced pleasure of audiences. However, the neural mechanism underlying such modulation remains largely unexplored. This study utilized psychophysiological and electroencephalographic data collected from listeners as they watched and listened to manipulated vocal (Mandarin lyrics) and violin performances of Japanese and Chinese pop music. All participants were unfamiliar with the violin or Mandarin. The auditory and visual elements of the stimuli were either congruent (original recording) or incongruent (drawn from unrelated music videos). We found that congruent visual movements, as opposed to incongruent ones, increased both subjective pleasure ratings and skin conductance responses but only during vocal performances. Then, we examined the coherence between the music signal and sensorimotor Mu-band oscillatory neural activity and found that congruent visual movements enhanced Mu entrainment exclusively to vocal music signal. Further, mediation analysis demonstrated that neural entrainment to vocal music significantly mediated the visual modulation of music-induced pleasure. In conclusion, our study provides novel evidence on how congruent visual movements can heighten music-induced pleasure through enhanced sensorimotor integration.

How different immersive environments affect intracortical brain computer interfaces
As brain-computer interface (BCI) research advances, many new applications are being developed. Tasks can be performed in different environments, and whether a BCI user can switch environments seamlessly will influence the ultimate utility of a clinical device. Here we investigate the importance of the immersiveness of the virtual environment used to train BCI decoders on the resulting decoder and its generalizability between environments. Two participants who had intracortical electrodes implanted in their precentral gyrus used a BCI to control a virtual arm, either viewed immersively through virtual reality goggles or at a distance on a flat television monitor. Each participant performed better with a decoder trained and tested in the environment they had used the most prior to the study, one for each environment type. The neural tuning to the desired movement was minimally influenced by the immersiveness of the environment. Finally, in further testing with one of the participants, we found that decoders trained in one environment generalized well to the other environment, but the order in which the environments were experienced within a session mattered. Overall, experience with an environment was more influential on performance than the immersiveness of the environment, but BCI performance generalized well after accounting for experience.

Brain-responsive music enables non-invasive, targeted and unobtrusive neurostimulation
Objective: We are developing a new closed-loop brain stimulation method by embedding, within music, auditory elements that respond to the listeners brain activity. Here we show that this brain-responsive music has systematic and targeted effects on neural oscillations implicated in a variety of neurological and mental health disorders. Approach: We recorded magnetoencephalogram (MEG) or electroencephalogram (EEG) signals from participants as they listened to music synthesized by commercial audio software. Brain signals were bandpass filtered, phase-shifted and used to control the timbre and/or timing of notes within the music. Main results: Listening to brain-responsive music induced peaks and troughs in spectral power at frequencies that depended systematically on the phase-shift applied to the brain signal. Phase-dependent modulation was greatest at the centre frequency of the filter. As a result, by calibrating these parameters we could achieve selective enhancement or suppression of either theta (5 Hz) or alpha (10 Hz) oscillations. Moreover, by chosing different sensor locations we could target power modulation to either frontal or temporal cortex. The phase-dependent power modulation observed with brain-responsive music was significantly attenuated when participants listened to identical music as a conventional, open-loop stimulus. Finally, we demonstrate that brain activity could be modulated by more complex compositions combining a variety of brain-responsive musical elements controlled by a wireless, wearable EEG headband suitable for home use. Significance: Brain-responsive music provides an unobtrusive and targeted method of modulating neural oscillations in the listeners brain, and may enable both creative and therapeutic applications of Brain Computer Interface technologies.

Enhanced and idiosyncratic neural representations of personally typical scenes
Previous research shows that the typicality of visual scenes (i.e., if they are good examples of a category) determines how easily they can be perceived and represented in the brain. However, the unique visual diets individuals are exposed to across their lifetimes should sculpt very personal notions of typicality. Here, we thus investigated whether scenes that are more typical to individual observers are more accurately perceived and represented in the brain. We used drawings to enable participants to describe typical scenes (e.g., a kitchen) and converted these drawings into 3D renders. These renders were used as stimuli in a scene categorization task, during which we recorded EEG. In line with previous findings, categorization was most accurate for renders resembling the typical scene drawings of individual participants. Our EEG analyses reveal two critical insights on how these individual differences emerge on the neural level: First, personally typical scenes yielded enhanced neural representations from around 200 ms after onset. Second, personally typical scenes were represented in idiosyncratic ways, with reduced dependence on high-level visual features. We interpret these findings in a predictive processing framework, where individual differences in internal models of scene categories formed through experience shape visual analysis in idiosyncratic ways.

Cholecystokinin modulates age-dependent Thalamocortical Neuroplasticity
The thalamocortical pathway exhibits neuroplasticity not only during the critical period but also in adulthood. Here, we aimed to investigate the modulation of age-dependent thalamocortical plasticity by cholecystokinin (CCK). Our findings revealed the expression of CCK in thalamocortical neurons, and high-frequency stimulation (HFS) of the thalamocortical pathway elicited the release of CCK in auditory cortex (ACx), as evidenced by CCK sensor. HFS of the medial geniculate body (MGB) induced thalamocortical long-term potentiation (LTP) in wildtype young adult mice. However, knockdown of Cck expression in MGB neurons or blockade of the CCK-B receptor (CCKBR) in ACx effectively abolished HFS-induced LTP. Notably, this LTP could not be elicited in both juvenile mice (week 3) and mice over 18 months old, due to the absence of CCKBR in juvenile mice and the inability of CCK to be released in aged mice. Remarkably, the administration of exogenous CCK into the auditory cortex of the aged mice restored this LTP, accompanied by a significant improvement in frequency discrimination. These findings suggest the potential of CCK as a therapeutic intervention for addressing neurodegenerative deficits associated with thalamocortical neuroplasticity.

Cell-type-specific striatal modulation of amygdalar acetylcholine in salience assignment
The salience assignment is pivotal for both natural and artificial intelligence. Pioneering studies established that basal forebrain cholinergic neurons process behaviorally relevant salient information. However, the neural circuit mechanism underlying salience assignment remains poorly understood. Here we show that the acetylcholine (ACh) level in the basolateral amygdala (BLA) dynamically represented behavioral salience. Distinct neuronal subpopulations in the nucleus accumbens (NAc), D1- and D2-expressing medium spiny neurons (MSNs), antagonistically and specifically promote and suppress ACh release in the BLA, but not the cortex and hippocampus. These striatal D1 and D2 MSNs regulate BLA ACh by disinhibiting and inhibiting cholinergic neurons in the basal forebrain subregion substantia innominata (SI), respectively. Optogenetic manipulations of the pathway from striatal D1 and D2 MSNs to the SI opposingly affect associative learning. Our findings uncover an unconventional role of striatal MSNs in salience assignment via regulating the salience-representing amygdalar ACh activity.