bioRxiv Subject Collection: Neuroscience's Journal

'Eye Know': Gaze reflects confidence in explicit predictions while relying on a distinct computational mechanism
We learn by continuously forming associations to predict future events. This learning is manifested in both explicit decisions and implicit sensorimotor behaviors. Despite significant advances in understanding each of these learning systems, their computational interplay remains unclear. We explored the relationship between explicit predictions and oculomotor expectations during associative learning in virtual reality, across an exploratory and two additional pre-registered experiments (Total N = 115). Participants' explicit predictions about target location and their subsequent anticipatory gaze patterns both showed learning patterns. Moreover, gaze exhibited computational hallmarks of confidence in the explicit prediction, possibly reflecting an oculomotor confidence-like assessment. However, ocular and explicit learning also diverged significantly. Oculomotor learning exhibited reduced accuracy and metacognitive sensitivity relative to explicit responses. Oculomotor's computational learning mechanism was characterized by more exploratory behavior, increased rule changes, and reduced perseverance. These findings suggest complementary learning processes for explicit and oculomotor systems that enable adaptive behavior.

Dopamine and temporal discounting: revisiting pharmacology and individual differences
Disorders characterised by changes in dopamine (DA) neurotransmission are often linked to changes in the temporal discounting of future rewards. Likewise, pharmacological manipulations of DA neurotransmission in healthy individuals modulates temporal discounting, but there is considerable variability in the directionality of reported pharmacological effects, as enhancements and reductions of DA signalling have been linked to both increases and reductions of temporal discounting. This may be due to meaningful individual differences in drug effects and/or false positive findings in small samples. To resolve these inconsistencies, we 1) revisited pharmacological effects of the DA precursor L-DOPA on temporal discounting in a large sample of N = 76 healthy participants (n = 44 male) and 2) examined several putative proxy measures for DA to revisit the role of individual differences in a randomised, double-blind placebo-controlled pre-registered study (https://osf.io/a4k9j/). Replicating previous findings, higher rewards were discounted less (magnitude effect). Computational modelling using hierarchical Bayesian estimation confirmed that the data in both drug conditions were best accounted for by a non-linear temporal discounting drift diffusion model. In line with recent animal and human work, L-DOPA reliably reduced the discount rate with a small effect size, challenging earlier findings in substantially smaller samples. We found no credible evidence for linear or quadratic effects of putative DA proxy measures on model parameters, calling into question the role of these measures in accounting for individual differences in DA drug effects.

Mouse olfactory system acts as anemo-detector and -discriminator
Airflow detection while smelling is a fundamental requirement for olfaction, yet the mechanisms underlying such multimodal processing in the olfactory system remain unknown. We report here that mice can learn to accurately discriminate airflow with parallel processing of both mechanical and chemical stimuli revealed by modulated sniffing and refined calcium signaling in the olfactory bulb inhibitory network. Genetic perturbation of AMPAR function and optogenetic control bidirectionally shifted airflow discrimination learning pace, with contrasting phenotypes observed for odor learning, engagement of inhibitory circuits, and setting the optimal inhibition level for stimulus refinement. Multimodal odor-airflow stimuli at subthreshold levels enhanced learning, demonstrating that mechanical stimuli heighten olfactory perception. Our results, thus explain the multimodality of olfaction, and reveal an unexplored dimensionality of odor perception.

Handy divisions: Hand-specific specialization of prehensile control in bimanual tasks
When hammering a nail, why do right-handers wield the hammer in the right hand? The dynamic dominance theory suggests a somewhat surprising answer. The two hands are specialized for different types of tasks: the dominant for manipulating objects, and the non-dominant for stabilizing objects. Right-handers wield the moving object with their right hand to leverage the skills of both hands. Functional specialization in hand use is often illustrated using examples of object manipulation. However, the dynamic dominance theory is supported by wrist kinematics rather than object manipulation data. Therefore, our goal was to determine whether this theory extends to object manipulation. We hypothesized that hand-specific differences will be evident in the kinematics of hand-held objects and in the control of grip forces. Right-handed individuals held two instrumented objects that were coupled by a spring. They moved one object while stabilizing the other object in various bimanual tasks. They performed motions of varying difficulty by tracking predictable or unpredictable targets. The two hands switched roles (stabilization vs movement) in various experimental blocks. The changing spring length perturbed both objects. We quantified the movement performance by measuring the object positions, and grip force control by measuring grip-load coupling in the moving hand and mean grip force in the stabilizing hand. The right hand produced more accurate object movement, along with stronger grip-load coupling, indicating superior predictive control of the right hand. In contrast, the left hand stabilized the object better and exerted a higher grip force, indicating superior impedance control of the left hand. Task difficulty had a weak effect on grip-load coupling during object movement and no effect on mean grip force during object stabilization. These results suggest that dynamic dominance extends to object manipulation, though the weak effect of task difficulty on grip characteristics warrants further investigation.

Headache-specific Hyperexcitation Sensitises and Habituates on different Time Scales: An Event Related Potential study of Pattern-Glare
Cortical hyperexcitability is a key pathophysiological feature in several neurological disorders, including migraine, epilepsy, tinnitus, and Alzheimers disease. We examined the temporal characteristics of Evoked Related Potentials (ERPs) in a healthy population using the Pattern Glare Test, a diagnostic tool used to assess patients with sensitivity to cortical hyperexcitability. During the experiment, participants recorded state measures with this study focussing on susceptibility to migraine. We investigated two timeframes: habituation over the course of the experiment and sensitization over the course of stimulus presentation. We found evidence of hyperexcitability in the visual cortex, for the clinically aggravating stimuli (medium). Participants who reported a higher state measure exhibited a higher degree of habituation and sensitization, which was dependent on susceptibility to migraine. These findings suggest that the same experimental paradigm and analysis should be performed on a clinically diagnosed population.

Region-specific Nucleus Accumbens Dopamine Signals Encode Distinct Aspects of Avoidance Learning
Avoidance learning, learning to avoid bad outcomes, is an essential survival behavior. Dopamine signals are widely observed in response to aversive stimuli, indicating they could play a role in learning about how to avoid these stimuli. However, it is unclear what computations dopamine signals perform to support avoidance learning. Furthermore, substantial heterogeneity in dopamine responses to aversive stimuli has been observed across nucleus accumbens (NAc) subregions. To understand how heterogeneous dopamine responses to aversive stimuli contribute to avoidance learning, we recorded NAc core (Core) and NAc ventromedial shell (vmShell) dopamine during a task in which mice could avoid a footshock punishment by moving to the opposite side of a 2-chamber apparatus during a five-second warning cue. We found that NAc Core and vmShell dopamine signals responded oppositely during shocks and warning cues. Both signals evolved substantially, but differently, with learning. NAc vmShell dopamine responses to cues and shocks were present during early learning but not sustained during expert performance. NAc Core dopamine responses strengthen with learning and are especially evident during expert performance. Our data support a model in which NAc vmShell dopamine guides initial cue-shock associations by signaling salience, while NAc Core dopamine encodes prediction errors that guide the consolidation of avoidance learning.

Glutamate uptake is transiently compromised in the perilesional cortex following controlled cortical impact
Glutamate, the primary excitatory neurotransmitter in the CNS, is regulated by the excitatory amino acid transporters (EAATs) GLT-1 and GLAST. Following traumatic brain injury (TBI), extracellular glutamate levels increase, contributing to excitotoxicity, circuit dysfunction, and morbidity. Increased neuronal glutamate release and compromised astrocyte-mediated uptake contribute to elevated glutamate, but the mechanistic and spatiotemporal underpinnings of these changes are not well established. Using the controlled cortical impact (CCI) model of TBI and iGluSnFR glutamate imaging, we quantified extracellular glutamate dynamics after injury. Three days post-injury, glutamate release was increased, and glutamate uptake and GLT-1 expression were reduced. 7- and 14-days post-injury, glutamate dynamics were comparable between sham and CCI animals. Changes in peak glutamate response were unique to specific cortical layers and proximity to injury. This was likely driven by increases in glutamate release, which was spatially heterogenous, rather than reduced uptake, which was spatially uniform. The astrocyte K+ channel, Kir4.1, regulates activity-dependent slowing of glutamate uptake. Surprisingly, Kir4.1 was unchanged after CCI and accordingly, activity-dependent slowing of glutamate uptake was unaltered. This dynamic glutamate dysregulation after TBI underscores a brief period in which disrupted glutamate uptake may contribute to dysfunction and highlights a potential therapeutic window to restore glutamate homeostasis.

Selective autophagy fine-tunes Stat92E activity by degrading Su(var)2-10/PIAS during glial injury signalling in Drosophila
Glial immunity plays a pivotal role in the maintenance of nervous system homeostasis and responses to stress conditions, including neural injuries. In Drosophila melanogaster, the transcription factor Stat92E is activated in glial cells following central nervous system injury, independently of the canonical JAK/STAT pathway, to shape glial reactivity towards degenerated axons. However, the upstream regulatory mechanisms governing Stat92E activation remain elusive. Here, we reveal a selective autophagy-mediated regulation of Stat92E in glia by the degradation of the Stat92E repressor Su(var)2-10, a member of the PIAS SUMO ligase family. Atg8a, a core autophagy factor co-localizes and interacts with Su(var)2-10. Su(var)2-10 elimination is required for efficient Stat92E-dependent transcription after injury. Furthermore, we demonstrate that autophagy is essential for the upregulation of immune pathways, exemplified by virus-induced RNA 1 (vir-1), in glial cells following axon injury. We propose that Stat92E function is gated both by activating phosphorylation and autophagic Su(var)2-10 breakdown to licence glial reactivity. These findings underscore the critical role of autophagy in glial immunity and its potential impact on neural injury responses.

Dissociation of putative open loop circuit from ventral putamen to motor cortical areas in humans I: high-resolution connectomics
Human movement is partly organized and executed by cortico-basal ganglia-thalamic closed-loop circuits (CLCs), wherein motor cortical areas both send inputs to and receive feedback from the basal ganglia, particularly the dorsal putamen (PUTd). These networks are compromised in Parkinson's disease (PD) due to neurodegeneration of dopaminergic inputs primarily to PUTd. Yet, fluid movement in PD can sporadically occur, especially when induced by emotionally arousing events. Rabies virus tracing in non-human primates has identified a potential alternative motor pathway, wherein the ventral putamen (PUTv) receives inputs from subcortical limbic areas (such as amygdala nuclei) and sends outputs to motor cortical areas putatively via the nucleus basalis of Meynert (NBM). We hypothesize that this separable open loop circuit (OLC) may exist in humans and explain the preservation of movement after CLC degradation. Here, we provide evidence for the normal human OLC with ultra-high field (7T), multi-echo functional magnetic resonance imaging. We acquired resting-state functional connectivity (FC) scans from 21 healthy adults (avg. age = 29, 12M/9F, all right-handed) and mapped left-hemisphere seed-to-voxel connectivity to assess PUTv FC with putative subcortical nodes and motor cortical areas. We found that putative OLC node (basolateral amygdala, NBM) FC was greater with PUTv (p < 0.05), while CLC subcortical seed (ventrolateral nucleus of thalamus) FC was greater with PUTd (p < 0.01). Striatal FC patterns varied across cortical motor areas, with cingulate (p < 0.0001) and supplementary (p < 0.0001) motor areas showing greater FC with PUTv vs. nucleus accumbens. SMA had greater FC with PUTd vs. PUTv (p < 0.0001), while cingulate and primary motor areas showed no significant differences in FC between PUTd and PUTv (p > 0.1). Collectively, these results suggest that PUTv is functionally connected to motor cortical areas and may be integrated into a separable motor OLC with subcortical limbic inputs.

Using in vivo calcium imaging and home cage behavioural analysis to study pain in mouse models of rheumatoid- and osteo-arthritis
Objective: The purpose of this study was to evaluate the use of in vivo calcium imaging to monitor activity in joint afferents and group-housed home cage monitoring for the assessment of pain-like behaviors in mouse models of rheumatoid- and osteo-arthritis. Methods: Antigen induced arthritis (AIA) was used to model rheumatoid arthritis and partial medial meniscectomy (PMX) was used to model osteoarthritis. Group-housed home cage monitoring was used to assess behaviour in all mice, and weight bearing was performed in PMX mice. In vivo calcium with GCaMP6s was used to monitor spontaneous activity in L4 ganglion joint neurons retrogradely labelled with fast blue 2 days following AIA and 13-15 weeks following PMX. Cartilage degradation was assessed in knee joint sections stained with Safranin O and Fast Green in PMX mice. Results: Antigen induced arthritis produced knee joint swelling and PMX caused degeneration of articular cartilage in the knee. In the first 46 hours following AIA, mice travelled less distance and were less mobile compared to their control cage mates. In contrast, these parameters were similar between PMX and sham mice between 4-12 weeks post-surgery. Joint neurons had increased spontaneous activity in AIA but not PMX mice. Spontaneous activity was mostly localized to medium-sized neurons in AIA mice and was not correlated with any of the home cage behaviors. Conclusion: We conclude that group-housed home cage monitoring is a suitable technique for assessing joint pain behaviour in AIA mice. In vivo imaging of joint afferents revealed increased spontaneous activity in AIA but not PMX mice.

Inflammatory pain in mice induces light cycle-dependent effects on sleep architecture
As a syndrome, chronic pain comprises physical, emotional, and cognitive symptoms such as disability, negative affect, feelings of stress, and fatigue. A rodent model of long-term inflammatory pain, induced by complete Freund's adjuvant (CFA) injection, has previously been shown to cause anhedonia and dysregulated naturalistic behaviors, in a manner similar to animal models of stress. We examined whether this extended to alterations in circadian rhythms and sleep, such as those induced by chronic social defeat stress, using actigraphy and wireless EEG. CFA-induced inflammatory pain profoundly altered sleep architecture in male and female mice. Injection of the hind paw, whether with CFA or saline, reduced some measures of circadian rhythmicity such as variance, period, and amplitude. CFA increased sleep duration primarily in the dark phase, while sleep bout length was decreased in the light and increased in the dark phase. Additionally, CFA reduced wake bout length, especially during the dark phase. Increases in REM and SWS duration and bouts were most significant in the dark phase, regardless of whether CFA had been injected at its onset or 12 hours prior. Taken together, these results indicate that inflammatory pain acutely promotes but also fragments sleep.

Individual Differences in Cognition and Perception Predict Neural Processing of Speech in Noise for Audiometrically Normal Listeners.
Individuals with normal hearing exhibit considerable variability in their capacity to understand speech in noisy environments. Previous research suggests the cause of this variance may be due to individual differences in cognition and auditory perception. To investigate the impact of cognitive and perceptual differences on speech comprehension, 25 adult human participants with normal hearing completed numerous cognitive and psychoacoustic tasks including the Flanker, Stroop, Trail Making, Reading Span, and temporal fine structure (TFS) tests. They also completed a continuous multi-talker spatial attention task while neural activity was recorded using electroencephalography (EEG). The auditory cortical N1 response was extracted as a measure of neural speech encoding during continuous speech listening using an engineered "chirped-speech" (Cheech) stimulus. We compared N1 component morphologies of target and masker speech stimuli to assess neural correlates of attentional gains while listening to concurrently played short story narratives. Performance on cognitive and psychoacoustic tasks were used to predict N1 component amplitude differences between attended and unattended speech using multiple regression. Results show inhibitory control and working memory abilities can predict N1 amplitude differences between the target and masker stories. Interestingly, none of the cognitive and psychoacoustic predictors correlated with behavioral speech-in-noise listening performance in the attention task, suggesting that neural measures may be more sensitive measures of cognitive and auditory processing as compared to behavioral measures alone.

Regulation of transposons within medium spiny neurons enables molecular and behavioral responses to cocaine
A more complete understanding of the molecular mechanisms by which substance use is encoded in the brain could illuminate novel strategies to treat substance use disorders, including cocaine use disorder (CUD). We have previously discovered that Zfp189, which encodes a Kruppel-associated box zinc finger protein (KZFP) transcription factor (TF), differentially accumulates in nucleus accumbens (NAc) Drd1+ and Drd2+ medium spiny neurons (MSNs) over the course of cocaine exposure and is causal in producing MSN functional and behavioral changes to cocaine(1). Here, we aimed to illuminate the brain cell-type specific molecular mechanisms through which this KZFP TF produces CUD-related brain changes, with emphasis on investigating transposable elements (TEs), since KZFPs like ZFP189 are known regulators of TEs(2-6). First, we annotated TEs in existing single nuclei RNA-sequencing (snRNAseq) datasets of rodents that were exposed to either acute or repeated cocaine. We discovered that expression of NAc TEs was dramatically altered by cocaine experience, the most sensitive NAc cell-type was MSNs, and TEs in Drd1+ MSNs were considerably more dynamic over the course of cocaine exposure than TEs in Drd2+ MSNs. To determine the causality of this TE dysregulation within NAc MSNs in cocaine-induced brain changes, we virally delivered conditional synthetic ZFP189 TFs of our own design to Drd1+ or Drd2+ MSNs. These synthetic ZFP189 TFs are capable of directly activating (ZFP189VPR) or repressing (ZFP189WT) brain TEs2. We discover that behavioral and cell morphological adaptations to cocaine are produced by activating TEs with ZFP189VPR in Drd1+ MSNs or stabilizing TEs with ZFP189WT in Drd2+ MSNs, revealing a persistent opponent process balanced across MSN subtypes and weighted by TE stability and consequent gene expression within MSN subtype. We next performed snRNAseq of the whole NAc virally manipulated with ZFP189 TFs. We observed that, relative to ZFP189WT, NAc manipulated with ZFP189VPR impeded cocaine-induced gene expression in NAc cell-types, including both Drd1+ and Drd2+ MSNs. Within either MSN subtype, the consequence of normal ZFP189 function was to enhance immune-related gene expression, and ZFP189VPR impeded these gene expression profiles. We finally performed cocaine intravenous self-administration to determine the consequence of NAc ZFP189-mediated transcriptional control on cocaine use behaviors. We observed that ZFP189VPR impeded any increases in active lever responses following a period forced cocaine abstinence. This research demonstrates that KZFP-mediated transcriptional repression of TEs within NAc MSNs is a causal molecular step in enabling gene expression and subsequent cellular and behavioral responses to cocaine use, and the use of ZFP189VPR in this work demonstrates cell-type specific mechanistic strategies to block CUD-related brain adaptations, which may inform future CUD treatments.

Altered Copper Transport in Oxidative Stress-Dependent Brain Endothelial Barrier Dysfunction Associated with Alzheimer's Disease
Oxidative stress and blood-brain barrier (BBB) disruption due to brain endothelial barrier dysfunction contribute to Alzheimer's Disease (AD), which is characterized by beta-amyloid (A{beta}) accumulation in senile plaques. Copper (Cu) is implicated in AD pathology and its levels are tightly controlled by several Cu transport proteins. However, their expression and role in AD, particularly in relation to brain endothelial barrier function remains unclear. In this study, we examined the expression of Cu transport proteins in the brains of AD mouse models as well as their involvement in A{beta}42-induced brain endothelial barrier dysfunction. We found that the Cu uptake transporter CTR1 was upregulated, while the Cu exporter ATP7A and/or ATP7B were downregulated in the hippocampus of AD mouse models, and in A{beta}42-treated human brain microvascular endothelial cells (hBMECs). In the 5xFAD AD mouse model, Cu levels (assessed by ICP-MS) were elevated in the hippocampus. Moreover, A{beta}42-induced reactive oxygen species (ROS) production, ROS-dependent loss in barrier function in hBMEC (measured by transendothelial electrical resistance), and tyrosine phosphorylation of VE-cadherin were all inhibited by either a membrane permeable Cu chelator or by knocking down CTR1 expression. These findings suggest that dysregulated expression of Cu transport proteins may lead to intracellular Cu accumulation in the AD brain, and that A{beta}42 promotes ROS-dependent brain endothelial barrier dysfunction and VE-Cadherin phosphorylation in a CTR1-Cu-dependent manner. Our study uncovers the critical role of Cu transport proteins in oxidative stress-related loss of BBB integrity in AD.

FREQuency-resolved brain Network Estimation via Source Separation (FREQ-NESS)
The brain is a dynamic system whose network organisation is often studied by focusing on specific frequency bands or anatomical regions, leading to fragmented insights, or by employing complex and elaborate methods that hinder straightforward interpretations. To address this issue, we introduce a novel method called FREQuency-resolved Network Estimation via Source Separation (FREQ-NESS). This method is designed to estimate the activation and spatial configuration of simultaneous brain networks across frequencies by analysing the frequency-resolved multivariate covariance between whole-brain voxel time series. We applied FREQ-NESS to source-reconstructed magnetoencephalography (MEG) data during resting state and isochronous auditory stimulation. Results revealed simultaneous, frequency-specific brain networks in resting state, such as the default mode, alpha-band, and motor-beta networks. During auditory stimulation, FREQ-NESS detected: (1) emergence of networks attuned to the stimulation frequency, (2) spatial reorganisation of existing networks, such as alpha-band networks shifting from occipital to sensorimotor areas, (3) stability of networks unaffected by auditory stimuli. Furthermore, auditory stimulation significantly enhanced cross-frequency coupling, with the phase of attuned auditory networks modulating the gamma band amplitude of medial temporal lobe networks. In conclusion, FREQ-NESS effectively maps the brains spatiotemporal dynamics, providing a comprehensive view of brain function by revealing simultaneous, frequency-resolved networks and their interaction.

Segregated basal ganglia output pathways correspond to genetically divergent neuronal subclasses
The basal ganglia control multiple sensorimotor behaviors though anatomically segregated and topographically organized subcircuits with outputs to specific downstream circuits. However, it is unclear how the anatomical organization of basal ganglia output circuits relates to the molecular diversity of cell types. Here, we demonstrate that the major output nucleus of the basal ganglia, the substantia nigra pars reticulata (SNr) is comprised of transcriptomically distinct subclasses that reflect its distinct progenitor lineages. We show that these subclasses are topographically organized within SNr, project to distinct targets in the midbrain and hindbrain, and receive inputs from different striatal subregions. Finally, we show that these mouse subclasses are also identifiable in human SNr neurons, suggesting that the genetic organization of SNr is evolutionarily conserved. These findings provide a unifying logic for how the developmental specification of diverse SNr neurons relates to the anatomical organization of basal ganglia circuits controlling specialized downstream brain regions.

Transitions from monotonic to tuned responses in recurrent neural network models during timing prediction
The brain exhibits a gradual transition in responses to visual event duration and frequency through the visual processing hierarchy: from monotonically increasing to timing-tuned responses. Over their hierarchies, properties of both response types are progressively transformed. Here, we implement simulations based on artificial neural networks to investigate the requirements of neural systems for the emergence of such responses and their properties' transformations. We see that recurrent networks develop monotonic responses whose properties' progressions over network layers resemble those over brain areas. Furthermore, recurrent networks can further develop tuned responses, but only with training, a gradual transition between monotonic and tuned responses emerges. Particularly, if this training is done on predictable sequences, the tuned properties' progressions resemble those observed in the brain. These results suggest that the emergence of visual timing-tuned responses and the subsequent hierarchical transformations of these responses result from recurrent neural computation and predictive processing of sensory event timing.

Liprin-α/RIM complex regulates the dynamic assembly of presynaptic active zones via liquid-liquid phase separation
Presynaptic scaffold proteins, including liprin-, RIM, and ELKS, are pivotal to the assembly of the active zone and regulating the coupling of calcium signals and neurotransmitter release, yet the underlying mechanism remains poorly understood. Here, we determined the crystal structure of the liprin-2/RIM1 complex, revealing a multifaceted intermolecular interaction that drives the liprin-/RIM assembly. Neurodevelopmental disease-associated mutations block the formation of the complex. Disrupting this interaction in neurons impairs synaptic transmission and reduces the readily releasable pool of synaptic vesicles. Super-resolution imaging analysis supports a role for liprin- in recruiting RIM1 to the active zone, presumably by promoting the liquid-liquid phase separation (LLPS) of RIM1. Strikingly, the liprin-/RIM interaction modulates the competitive distribution of ELKS1 and voltage-gated calcium channels (VGCCs) in RIM1 condensates. Disrupting the liprin-/RIM interaction significantly decreased VGCC accumulation in the condensed phase and rendered release more sensitive to the slow calcium buffer EGTA, suggesting an increased physical distance between VGCC and vesicular calcium sensors. Together, our findings provide a plausible mechanism of the liprin-/RIM complex in regulating the coupling of calcium channels and primed synaptic vesicles via LLPS for efficient synaptic transmission and uncover the pathological implication of liprin- mutations in neurodevelopmental disorders.

Defensive freezing sharpens threat-reward information processing during approach-avoidance decision making
People regularly face approach-avoidance dilemmas which require minimization of potential threat whilst maximizing potential reward. Defensive reactions to threat, such as transient states of freezing, influence integration of reward/threat information in the dorsal Anterior Cingulate Cortex (dACC). However, the mechanism of this integration between internal state and external value (state-value integration) remains unknown. Here, we decoded approach-avoidance decisions under threat using high-precision magnetoencephalography (MEG). Threat-induced cardiac deceleration (indicative of defensive freezing) was trial-by-trial associated with more pronounced effects of reward and threat magnitudes on approach-avoidance choices. Time-resolved decoding of threat-reward information from neural signals predicted approach-avoidance choices several seconds before the actual response. Crucially, during freezing, 6-12 Hz coherence between threat-reward information and dACC neural activity increased, suggesting that defensive freezing sharpens threat/reward processing during approach-avoidance decision making. These findings provide a potential neural mechanism by which threat-induced freezing can facilitate information integration, essential for optimal decision making under threat.

Transformations in prefrontal ensemble activity underlying rapid threat avoidance learning
The capacity to learn cues that predict aversive outcomes, and understand how to avoid those outcomes, is critical for adaptive behavior. Naturalistic avoidance often means accessing a safe location, but whether a location is safe depends on the nature of the impending threat. These relationships must be rapidly learned if animals are to survive. The prelimbic subregion (PL) of the medial prefrontal cortex (mPFC) integrates learned associations to influence these threat avoidance strategies. Prior work has focused on the role of PL activity in avoidance behaviors that are fully established, leaving the prefrontal mechanisms that drive rapid avoidance learning poorly understood. To determine when and how these learning-related changes emerge, we recorded PL neural activity using miniscope calcium imaging as mice rapidly learned to avoid a threatening cue by accessing a safe location. Over the course of learning, we observed enhanced modulation of PL activity representing intersections of a threatening cue with safe or risky locations and movements between them. We observed rapid changes in PL population dynamics that preceded changes observable in the encoding of individual neurons. Successful avoidance could be predicted from cue-related population dynamics during early learning. Population dynamics during specific epochs of the conditioned tone period correlated with the modeled learning rates of individual animals. In contrast, changes in single-neuron encoding occurred later, once an avoidance strategy had stabilized. Together, our findings reveal the sequence of PL changes that characterize rapid threat avoidance learning.

Developmental transformations of Purkinje cells tracked by DNA electrokinetic mobility
Brain development relies on orchestrated placement and timing of neurogenesis in progenitor zones to produce the expansive cellular diversity of the brain. We took advantage of bioelectric interactions between DNA and embryonic tissue to perform "stereo-tracking", a developmental targeting strategy that differentially labels cells positioned at different depths within intact progenitor zones. This three-dimensional labeling was achieved by delivery of plasmids with distinct electrokinetic mobilities into neural progenitor zones in utero. We applied stereo-tracking with light sheet imaging in the cerebellum and identified that Purkinje cells follow embryonically committed developmental trajectories linking distinct progenitor zone fields to the topography of the mature cerebellar cortex. In the process of stereo-tracking, we identified a previously unreported subcellular structure on the axon initial segment of Purkinje cells. These structures, we termed "axon bubbles", are developmentally timed and differentially labeled by lipid-modified proteins. Our findings demonstrate key rules that orchestrate the stereotyped transformations from fetal progenitors into mature networks of neuronal circuits, and demonstrate the potential of progenitor zone stereo-tracking to reveal new biology within intact developing systems.

Otoacoustic emissions predict cochlear-nerve but not behavioral frequency tuning in an avian vocal-communication specialist
Frequency analysis by the cochlea forms a key foundation for all subsequent auditory processing. Stimulus-frequency otoacoustic emissions (SFOAEs) are a potentially powerful alternative to traditional behavioral experiments for estimating cochlear tuning without invasive testing, as is necessary in humans. Which methods accurately predict cochlear tuning remains controversial due to only a single animal study comparing SFOAE-based, behavioral, and cochlear frequency tuning in the same species. The budgerigar is a parakeet species with human-like behavioral sensitivity to many sounds and the capacity to mimic speech. Multiple studies show that budgerigars exhibit a perceptual auditory fovea with sharpest behavioral frequency tuning at mid frequencies from 3.5-4 kHz, in contrast to the typical pattern of monotonically increasing tuning sharpness for higher characteristic frequencies. We measured SFOAE-based and cochlear-afferent tuning in budgerigars, for comparison to previously reported behavioral results. SFOAE-based and cochlear-afferent tuning sharpness both increased monotonically for higher frequencies, in contrast to the behavioral pattern. Thus, SFOAE-based tuning in budgerigars accurately predicted cochlear tuning, and both measures aligned with typical patterns of cochlear frequency tuning in other species. Given divergent behavioral tuning in the budgerigars, which could reflect specializations for central processing of masked signals, these results highlight the value of SFOAEs for estimating cochlear tuning and caution against direct inference of cochlear tuning from behavioral results.

Movement-related activity in the internal globus pallidus of the parkinsonian macaque
Although the basal ganglia (BG) plays a central role in the motor symptoms of Parkinson's disease, few studies have investigated the influence of parkinsonism on movement-related activity in the BG. Here, we studied the perimovement activity of neurons in globus pallidus internus (GPi) of non-human primates before and after the induction of parkinsonism by administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Neuronal responses were equally common in the parkinsonian brain as seen prior to MPTP and the distribution of different response types was largely unchanged. The slowing of behavioral reaction times and movement durations following the induction of parkinsonism was accompanied by a prolongation of the time interval between neuronal response onset and movement initiation. Neuronal responses were also reduced in magnitude and prolonged in duration after the induction of parkinsonism. Importantly, those two effects were more pronounced among decrease-type responses, and they persisted after controlling for MPTP-induced changes in the trial-by-trial timing of neuronal responses. Following MPTP The timing of neuronal responses also became uncoupled from the time of movement onset and more variable from trial-to-trial. Overall, the effects of MPTP on temporal features of neural responses correlated most consistently with the severity of parkinsonian motor impairments whereas the changes in response magnitude and duration were either anticorrelated with symptom severity or inconsistent. These findings point to a potential previously underappreciated role for abnormalities in the timing of GPi task-related activity in the generation of parkinsonian motor signs.

GPRC6A as a novel kokumi receptor responsible for enhanced taste preferences by ornithine
In recent years, the concept of "kokumi" has garnered significant attention in gustatory physiology and food science. Kokumi refers to the enhanced and more delicious state of food flavor. However, the underlying neuroscientific mechanisms remain largely unexplored. Our previous research demonstrated that ornithine (L-ornithine), abundantly found in shijimi clams, enhances taste preferences. This study aims to build on these findings and investigate the mechanisms behind kokumi. In a two-bottle preference test in rats, the addition of ornithine, at a concentration without specific taste, enhanced the preference for solutions of umami, sweetness, fatty taste, saltiness, and bitterness, with monosodium glutamate intake showing the most significant increase. A mixture of umami and ornithine induced synergistically large responses in the chorda tympani nerve, which transmits taste information from the anterior part of the tongue. This enhancement of preference and the increase in taste nerve response were abolished by antagonists of the G-protein-coupled receptor family C group 6 subtype A (GPRC6A). Immunohistochemical experiments indicated that GPRC6A is expressed in a subset of type II taste cells in the fungiform papillae. These results provide new insights into flavor enhancement mechanisms, suggesting that ornithine is a newly identified kokumi substance and GPRC6A is a novel kokumi receptor.

Estrus-Tracking Cortical Neurons Integrate Social cues and Reproductive states to Adaptively Control Sexually Dimorphic Sociosexual Behaviors
Female sociosexual behaviors, essential for survival and reproduction, are adaptively modulated by ovarian hormones. However, the neural mechanisms integrating internal hormonal states with external social cues to guide these behaviors remain poorly understood. Here we identified primary estrous-sensitive Cacna1h-expressing medial prefrontal (mPFCCacna1h+) neurons that orchestrate adaptive sociosexual behaviors. Bidirectional manipulation of mPFCCacna1h+ neurons drives opposite-sex-directed behavioral shifts between estrus and diestrus females. In males, these neurons serve opposite functions compared to estrus females, mediating sexually dimorphic effects via anterior hypothalamic outputs. Miniscope imaging reveals mixed-representation of self-estrous states and social target sex in distinct mPFCCacna1h+ subpopulations, with biased-encoding of opposite-sex social cues in estrus females and males. Mechanistically, ovarian hormone-driven upregulation of Cacna1h-encoded T-type calcium channels underlies estrus-specific activity changes and sexual-dimorphic function of mPFCCacna1h+ neurons. These findings uncover a prefrontal circuit that integrates internal hormonal states and target-sex information to exert sexually bivalent top-down control over adaptive social behaviors.

Reduced neural distinctiveness of speech representations in the middle-aged brain
Speech perception declines independent of hearing thresholds in middle-age, and the neurobiological reasons are unclear. In line with the age-related neural dedifferentiation hypothesis, we predicted that middle-aged adults show less distinct cortical representations of phonemes and acoustic-phonetic features relative to younger adults. In addition to an extensive audiological, auditory electrophysiological, and speech perceptual test battery, we measured electroencephalographic responses time-locked to phoneme instances (phoneme-related potential; PRP) in naturalistic, continuous speech and trained neural network classifiers to predict phonemes from these responses. Consistent with age-related neural dedifferentiation, phoneme predictions were less accurate, more uncertain, and involved a broader network for middle-aged adults compared with younger adults. Representational similarity analysis revealed that the featural relationship between phonemes was less robust in middle-age. Electrophysiological and behavioral measures revealed signatures of cochlear neural degeneration (CND) and speech perceptual deficits in middle-aged adults relative to younger adults. Consistent with prior work in animal models, signatures of CND were associated with greater cortical dedifferentiation, explaining nearly a third of the variance in PRP prediction accuracy together with measures of acoustic neural processing. Notably, even after controlling for CND signatures and acoustic processing abilities, age-group differences in PRP prediction accuracy remained. Overall, our results reveal "fuzzier" phonemic representations, suggesting that age-related cortical neural dedifferentiation can occur even in middle-age and may underlie speech perceptual challenges, despite a normal audiogram.

Global brain asymmetry and its variations in aging and related diseases
Functional lateralization is a cardinal feature of human brain, and deviations from typical lateralization are observed in various brain disorders. Although this phenomenon has been widely acknowledged in the field of human neuroscience, decades of research have shown that it is a challenge to bridge the gap between (a)typically lateralized functions and hemispheric differences in structure (termed structural asymmetry). To address this important question, the present study employed the state-of-the-art machine learning techniques to investigate the brain structural asymmetry and its associations with cognitive functions, aging, and aging-related diseases, by integrating large-scale datasets. Our proposed multivariate approach revealed previously unknown and substantial structural differences between the left and right hemispheres, and established the associations between the global brain asymmetry and lateralized functions including hand motor and emotion processing. Furthermore, at the population level we mapped the aging trajectories of the global brain asymmetry, and unveiled significant diagnosis-specific variations in patients with Alzheimer's disease and Parkinson's disease, and individuals carrying a relevant genetic risk for atypical brain aging (i.e., APOE4 carriers). These results demonstrated left-hemisphere-linked changes in aging, which has challenged the traditional "right hemi-aging" model, and offered a promising approach for assessing brain aging and related diseases. Overall, our study with a novel approach presents one of the largest-scale investigation of global brain asymmetry, and takes an important step forward in understanding the intricate interplay between structural asymmetry, lateralized functions, and brain aging in health and disease.

Brain Charts for the Rhesus Macaque Lifespan
Recent efforts to chart human brain growth across the lifespan using large-scale MRI data have provided reference standards for human brain development. However, similar models for nonhuman primate (NHP) growth are lacking. The rhesus macaque, a widely used NHP in translational neuroscience due to its similarities in brain anatomy, phylogenetics, cognitive, and social behaviors to humans, serves as an ideal NHP model. This study aimed to create normative growth charts for brain structure across the macaque lifespan, enhancing our understanding of neurodevelopment and aging, and facilitating cross-species translational research. Leveraging data from the PRIMatE Data Exchange (PRIME-DE) and other sources, we aggregated 1,522 MRI scans from 1,024 rhesus macaques. We mapped non-linear developmental trajectories for global and regional brain structural changes in volume, cortical thickness, and surface area over the lifespan. Our findings provided normative charts with centile scores for macaque brain structures and revealed key developmental milestones from prenatal stages to aging, highlighting both species-specific and comparable brain maturation patterns between macaques and humans. The charts offer a valuable resource for future NHP studies, particularly those with small sample sizes. Furthermore, the interactive open resource (https://interspeciesmap.childmind.org) supports cross-species comparisons to advance translational neuroscience research.