The Journal of Neuroscience

Effort-based decision-making, the process of weighing reward benefits against effort costs, is essential for adaptive behavior. Although the dorsal raphe nucleus (DRN) contributes to reward processing and effort-related behaviors, how specific DRN neuronal subtypes contribute to effort-based decision-making remains poorly understood. Using fiber photometry to record DRN serotonergic and GABAergic neurons during an effort-based decision-making task, we found that tonic fluctuations in DRN serotonergic activity were selectively associated with persistent selection of the high-value option. Furthermore, we found that while neither neuronal population was sensitive to relative reward magnitude, effort expenditure selectively enhanced decision- and reward-related signals carried by serotonergic and GABAergic neurons, respectively. Together, these findings support a cell type-specific model in which serotonergic activity provides a signal linking persistent motivational states to effortful choice, whereas GABAergic activity may contribute to evaluating or updating reward outcomes after effort expenditure. SIGNIFICANCE STATEMENTChoosing whether a reward is worth the effort required to obtain it is essential for adaptive behavior, yet the neural mechanisms underlying this process remain incompletely understood. Here, we identify distinct contributions of serotonin- and GABAergic neurons in the dorsal raphe nucleus, a major source of brain serotonin, to effort-based decision-making. Serotonergic neurons were preferentially engaged in sustained motivational state and action selection, and GABAergic neurons in the processing of reward outcomes following costly actions. Our findings reveal a cell type-specific organization of effort-based reward seeking in the dorsal raphe nucleus and provide a framework for understanding how motivational states, decisions, and reward outcomes are coordinated.

The small GTPase Rem2 is a key signaling molecule involved in synaptic formation, dendritic complexity, spine formation, and regulation of CaMKII-dependent long-term potentiation (LTP). However, it remains unclear how Rem2 explicitly impacts learning and memory. To address this issue, we deleted Rem2 specifically in dorsal CA1 neurons of male and female mice and assessed spatial learning using a spatial object recognition (SOR) task. We found that males outperform females in this behavioral assay and that deleting Rem2 did not impact spatial learning in males. In contrast, Rem2 deletion significantly improved spatial learning in females enabling them to perform as well as males in the SOR task. Using an automated Western blot system to assess all known AMPA- and NMDA-mediated glutamate receptor (AMPAR and NMDAR) subunits in each mouse, we found that the sex-dependent change in SOR we observed was likely due to Rem2 increasing GluN2D expression in the interneurons of female mice only. Furthermore, using S-statistics to compare the overall AMPAR and NMDAR composition among groups, we found that males and females normally have divergent covariance structures but this divergence is eliminated when Rem2 is deleted from CA1 neurons. These results reveal an unexpected role of Rem2 in maintaining sex differences in glutamate receptor composition and spatial learning abilities. To our knowledge, this is the first demonstration of a signaling molecule that confers sexual dimorphism to excitatory synapses. As such, Rem2 may play a critical role in understanding how sex-dependent symptoms of neurodevelopmental and neurodegenerative disorders arise.

The neural substrates of tactile long-term memory (LTM) in humans remain poorly understood, as relatively few neuroimaging studies have addressed this question. Here, we asked whether retrieval of tactile stimulation engages modality-specific representations in the primary and secondary somatosensory cortices (S1 and S2), alongside domain-general retrieval networks. Participants learned 16 tactile trajectories, each presented for 1.2 s on the left thumb through sequential activation of 10 vibrating dots on a Braille-like display. Three learning sessions within one week were followed by a recognition test during functional magnetic resonance imaging (fMRI). In the final sample (n = 26), we contrasted BOLD responses during successful recognition of learned stimuli with those during correct rejection of novel stimuli. Successful recognition was associated with increased activity in contralateral S1 and S2, alongside activation in the hippocampus as well as frontal and parietal regions implicated in memory retrieval. A psychophysiological interaction analysis (PPI) further revealed increased task-dependent connectivity between the hippocampus and contralateral S1 and S2 during successful recognition. Together, these findings suggest that tactile long-term memory retrieval relies on coordinated hippocampal-somatosensory interactions and may engage long-term memory representations in somatosensory cortex.

Animals confronted with increasing heat must switch from exploratory behavior to vigorous actions that limit further exposure, but the forebrain circuits controlling this transition are poorly understood. We exposed male mice to progressively stronger floor heating while providing continuous access to a climbing mesh separated from the heating plate. Higher plate settings shifted behavior from rearing toward wall-directed digging and climbing, with jumping at the highest setting, and increased c-Fos labeling in the median preoptic nucleus. Neurons expressing bombesin receptor subtype 3 showed greater c-Fos recruitment under strong heating, and their population calcium signals increased when mice entered the plate-controlled zone and decreased when they left. Optogenetic activation without heating produced place avoidance, vigorous actions, and increased locomotion. Inhibition reduced locomotion and, during strong heating, shifted behavior from climbing and jumping toward rearing and weakened avoidance of a localized heat source. These findings identify median preoptic Brs3-expressing neurons as regulators of behavioral escalation and heat avoidance.

Many individuals experience problems that are undetected by standard hearing tests, such as persistent tinnitus and difficulties understanding speech in background noise. Here, we report evidence of altered neural gain in young adults with self-reported listening problems despite exceptional hearing thresholds. Individuals reporting persistent tinnitus (the daily percept of sound in the absence of an external source) exhibited elevated thresholds of the middle ear muscle reflex, suggestive of altered gain in brainstem reflexive circuits, and reduced cortical responses to auditory spatial cues conveyed in the temporal fine structure of low-frequency sounds. Moreover, in both groups, greater self-reported speech-in-noise difficulties were associated with higher magnitude cortical responses, particularly at the highest stimulus intensity, consistent with elevated neural gain. Using a conceptual model, we demonstrate how damage to high-threshold auditory nerve fibres innervating cochlear nuclei can account for reduced activity of binaural neurons sensitive to the temporal fine structure of low-frequency sounds, generating a compensatory increase in neural gain in higher brain centres that impacts listening in complex environments.

Preterm birth is associated with an increased risk of later language difficulties, yet whether and how prematurity alters the brain's ability to track the rhythmic structure of speech has remained understudied. Using EEG, we tracked neural entrainment to delta- and theta-rate syllable sequences produced by the infant's mother or an unfamiliar speaker in term and preterm 6-month-old infants, modeling how oscillatory responses evolved over the course of a testing session. Term infants progressively strengthened frequency-matched delta tuning over bilateral frontal regions; preterm infants did not. This divergence took two distinct forms: a change in frequency selectivity over left frontal channels, where term infants sharpened and preterm infants blurred, and a shift in band weighting in other regions. The frontal delta difference emerged only for the unfamiliar speaker. Preterm birth thus alters how frequency-specific tuning is refined during exposure, identifying a candidate neural pathway with implications for early language learning.

Altered sensitivity to sounds despite normal peripheral hearing is common in neurodevelopmental disorders but the underlying mechanisms remain poorly understood. Here we investigate tonotopic organization in 86 children (6-11 years) with autism spectrum and related neurodevelopmental disorders as well as typically developing (TD) peers, using a child-friendly, passive listening, functional magnetic resonance imaging design. In TD children, tonotopic maps in primary auditory cortex resembled the typical high-low-high frequency gradients previously reported in adults, while children with autism showed an overrepresentation of high frequencies consistent with what has been observed in animal models of autism. Higher frequency tuning further correlated with greater caregiver-reported sound but not touch sensitivities. Importantly, tonotopy is a core organizational feature of auditory cortex that develops early in life and remains relatively stable after the critical period of heightened plasticity ends. Thus, these results suggest that atypical auditory processing in autism may result from early disruption to tonotopic map formation. Longitudinal neuroimaging studies are needed to understand the genetic and environmental causes of altered auditory cortex topology and its long-term consequences for higher-level auditory, language, and social communication development.

Despite their established role in motivated behavior, how nucleus accumbens (NAc) cholinergic interneurons (CINs) contribute to natural reward seeking remains unclear. Here, we report that NAc CINs are key modulators of the approach phase of reward pursuit. Using in vivo fiber photometry in Chat-ires-Cre mice, we show that NAc CINs are robustly activated during the approach towards several salient stimuli including food, a social target, and a familiar object. We also provide evidence that this activation is potentially driven by olfactory cues. Disrupting NAc CIN function via targeted expression of a membrane-tethered toxin results in a delayed approach towards both food and a social target, but no alterations in object investigation, general locomotion or anxiety-related measures. Together, these findings identify NAc CINs as regulators of the initiation of natural reward approach and suggest that they link sensory information with onset of motivated action.

Dopamine D1 receptors (D1R) and muscarinic M4 receptors (M4R) regulate overlapping functions in the cortex and the striatum, but the cellular relationship between D1R- and M4R-associated populations across brain regions remains incompletely defined. Using D1R-tdTomato/M4R-EGFP double-reporter mice, we quantified tdTomato-only, EGFP-only, and coexpressing cellular populations across the dorsal striatum, nucleus accumbens, and medial prefrontal cortex in 18 animals. Reporter composition differed strongly by anatomical region. Coexpression was prominent throughout the dorsal striatum and greatest in the dorsomedial striatum, whereas the nucleus accumbens shifted toward greater tdTomato-only and reduced EGFP-only representation, particularly in the core. In contrast, the medial prefrontal cortex was dominated by EGFP-only cells. These regional patterns were broadly retained across sex and age. HCR-FISH further supported spatial correspondence between endogenous Drd1 and Chrm4 transcript signal and the respective fluorescent reporters. Together, these findings demonstrate region-dependent organization of D1R- and M4R-associated cellular populations across the cortex and striatum and define distinct anatomical contexts in which M4R-directed signaling may influence D1R-associated neurons.

Ambient illumination influences many aspects of brain function, including responses to threats. One brain region proposed to mediate these effects is the periaqueductal gray (PAG), an evolutionarily conserved midbrain structure that contains multiple subpopulations of peptidergic neurons. Here we ask which cell types in the larval zebrafish PAG respond to changes in ambient illumination. By registering post hoc gene expression to neurons recorded during exposure to sensory stimuli, we show that GABAergic PAG neurons expressing the neuropeptide Relaxin-3 (rln3a+) are persistently activated by darkness, while a neighboring subpopulation of GABAergic PAG neurons expressing penka is not. Zebrafish lacking rln3a show a reduction in locomotion during darkness. We propose that darkness recruits Relaxin-3-releasing PAG neurons to promote vigilance and potentiate defense circuits. These results identify a specific peptidergic population of PAG neurons that are potentially relevant to behavioral state dysregulation associated with excessive darkness.

Axonal projections and precise synapse formation are essential for the establishment of functional neural circuits, and their dysregulation contributes to various psychiatric and neurodegenerative disorders. Although numerous extracellular cues secreted from surrounding tissues regulate axon guidance and synapse formation, the mechanisms by which neurons locally regulate terminal patterning within their projection fields remain poorly understood. Bone morphogenetic protein 4 (BMP4) is a classical morphogen that is involved in early neural tube patterning during development. However, its postnatal function remains unclear. Previous in vitro studies using hippocampal glutamatergic neurons demonstrated that BMP4 can act locally on axons to suppress synapse formation, raising the possibility that BMP4 regulates terminal differentiation after target innervation. Here, we investigated the role of BMP4 in postnatal cholinergic circuit development using cholinergic neuron-specific Bmp4 conditional knockout (Bmp4 cKO) mice, with adult analyses performed in males. Basal forebrain cholinergic neurons project extensively throughout the neocortex and are essential for higher brain functions, including arousal and attention. Bmp4 cKO mice exhibited increased cholinergic axon terminals in the neocortex, hippocampus, and amygdala, as well as increased axonal ramification in the neocortex without affecting cytoarchitectonic organization or cholinergic neuron numbers in the basal forebrain. These findings demonstrate that BMP4 functions as a negative regulator of cholinergic terminal formation and axonal arborization, suggesting that BMP4 may act locally to restrict cholinergic axonal expansion during neural circuit maturation.

Dystonia is a common movement disorder characterized by involuntary co-contraction of antagonist muscles, resulting in abnormal postures. The brain often appears grossly normal, suggesting dysfunctional neural activity as a cause. The basal ganglia are implicated in dystonia, but the causal patterns of neural activity remain unknown. We used a transgenic mouse model of human paroxysmal nonkinesigenic dyskinesia (PNKD), in which ethanol triggers dystonic attacks, to test the role of the substantia nigra pars reticulata (SNr), the primary output nucleus of the basal ganglia in rodents. The firing of SNr neurons was profoundly reduced in vivo during dystonic attacks. Multiple physiological approaches indicated that in PNKD mice, ethanol leads to depolarization block in SNr neurons. Indeed, pulsatile optical activation of inhibitory striatal inputs to SNr rescued firing and attenuated dystonia. In line with theories of basal ganglia dysfunction, these results suggest reduced activity in basal ganglia output nuclei causes dystonia.

Efficient processing of complex acoustic signals within noisy environments is a fundamental challenge for the auditory system. This study investigates the cortical representation of structured noise and vocalizations embedded in it using widefield calcium imaging with the high-speed Calcium indicator jGCaMP8m in the mouse auditory cortex. The spectrotemporal statistics of the structured noise were controllable, including its temporal variance and cross-frequency correlations. We find that structured noise invokes spatially and temporally complex neural responses across the auditory cortex that reflect the spectrotemporal properties of the noise. We identified partially distinct noise response components: noise onset responses showed stronger overlap with primary than secondary areas, while later suppression components did not show a significant primary-secondary bias. Vocalization-evoked responses were significantly attenuated in the presence of noise compared to silent contexts, exhibiting reduced onset magnitude and altered adaptation dynamics. Using decoding we find the neural representation of vocalizations to become more discriminable with longer preceding noise exposure. Furthermore, structured noise cochleograms could be reconstructed from neural population activity, with performance depending on stimulus statistics, tending to be higher in primary than secondary auditory cortex while remaining substantial across both. These findings suggest that the mouse auditory cortex represents acoustic targets in noise through context-dependent and spatially distributed population activity, shaped by both the statistical structure and temporal history of the acoustic background.

The relationship between neural processes supporting perception, deviance processing, and post-perceptual task demands during auditory processing is not well understood. We used multitone masking and a no-report inattentional deafness paradigm to dissociate neural correlates of auditory perceptual awareness, deviance processing, and task demands. Evoked responses to physically identical target-tone pairs were recorded across three phases differing only in task instructions. In Phase A, human participants remained nave to (and thus unaware of) the target tones. In Phase B, participants were informed about (and thus aware of) the target tones. In Phase C, participants remained aware of the target tones and judged the duration of the silent gap between them, rendering them task-relevant. When participants were aware of them, target tones elicited an auditory awareness negativity and an increased positivity in the P3 window), with larger responses when target tones were additionally task-relevant. Furthermore, though largest in Phase C, deviant stimuli elicited a mismatch negativity across all task conditions, while a significant P3 to deviants was only observed in Phase C. Thus, early and late responses can be independently modulated by awareness, deviance, and task-relevance, indicating that they do not necessarily rely on shared neural mechanisms despite overlapping spatiotemporal profiles.

Bimanual coordination requires the control of each hand to account for movements of the other hand. To enable such coordination, it has been hypothesized that the brain has a representation of bimanual movements that supersedes a linear combination of the unimanual movements. To test for such a representation, we mapped the encoding of movement direction during unimanual and bimanual wrist movements in the human brain using functional magnetic resonance imaging (fMRI). For unimanual movements, we found that both the contralateral and ipsilateral movement directions were represented across most cortical motor regions. The representations were similar for mirror-symmetric movements across the hands, revealing an intrinsic (body-centric) code in premotor and parietal regions. For bimanual movements, the neural representations of movement directions could be explained by three components. First, the contralateral movement direction was represented as in the unimanual condition, whereas the representation of the ipsilateral movement direction disappeared. Second, in higher-order regions (rostral premotor and posterior parietal cortex) we found relatively elevated activity when the two movements were directed in unrelated directions. This activity was likely caused by the extra effort to deal with incongruent spatial targets across the hands. Third, and independent of this congruency effect, we found a non-linear interaction between contra- and ipsilateral movement that encoded the specific bimanual movement combination across sensorimotor, premotor, and parietal regions. This representation was suited to facilitate bimanual coordination and learning.

The ventral lateral geniculate nucleus (GLv) is a conserved retinorecipient structure positioned between visual and premotor systems, yet its role in visuomotor transformations remains poorly understood. Here, we examined whether the pigeon GLv contains a spatially organized motor representation linking visual-field locations to orienting movements. Anatomical tracing identified descending projections from neurons in the GLv inner lamina (GLv-li) through pretectal and tegmental regions toward pontine targets. GLv-li projection neurons are GABAergic, yet electrical microstimulation of GLv-li in awake pigeons evoked rapid head movements followed by smaller eye movements. Each stimulation locus produced a reproducible characteristic motor vector whose direction and duration were largely insensitive to stimulation parameters, whereas movement amplitude and velocity approached site-specific plateaus. Movements initiated from different head positions were better explained by repetition of a fixed displacement than by convergence toward a common spatial goal. Critically, motor-vector direction was systematically related to the direction of the visual receptive field represented at the same GLv locus, while motor-vector amplitude covaried with receptive-field eccentricity. These defining features persisted after optic tectum ablation. Together, these findings reveal a retinotopically-organized map of fixed-vector head movements in the avian GLv and identify a tectum-independent route through which visual spatial representations can access descending orienting circuitry.

Chronic heavy alcohol use shifts brain metabolism from glucose toward acetate utilization. Sudden decreases in acetate following alcohol cessation in individuals with alcohol use disorder (AUD) may create an energetic imbalance that contributes to craving and withdrawal. A recent randomized study found that, compared with a standard American (SA) diet, a ketogenic diet (KD) during alcohol detoxification reduced withdrawal severity and craving and increased ketones and glutamate in the dorsal anterior cingulate cortex. These findings suggest that ketones may support metabolic adaptation during alcohol withdrawal, but the effects of altered brain metabolism on neural dynamics and alcohol cue reactivity remain unknown. Here, we used a control theoretic approach to test whether shifts in cerebral energy substrate utilization influence large-scale network dynamics through altered information flow. We analyzed fMRI cue-reactivity scans collected after one, two, and three weeks of inpatient treatment during presentation of alcohol, food, and neutral cues. Whole-brain effective connectivity was estimated using Shannon transfer entropy applied to whole brain atlas-aligned fMRI time series. Assuming neural activity flow along effective connections, we identified distinct shifts in the state-transition landscape in participants receiving the KD compared with the SA diet. Increases in serum {beta}-hydroxybutyrate (BHB) were associated with changes in state-transition landscape organization, which were in turn associated with reduced cue-induced alcohol craving. These findings link metabolic adaptation to large-scale neural dynamics and clinically relevant behavior and suggest that cerebral energy substrate availability may shape behavior by altering the organization of large-scale neural dynamics.

Face familiarity elicits reliable neural signatures during perception, yet how it is represented when faces are recalled from memory by using visual imagery and how these signals relate to perceptual representations, remains unclear. We combined perceptual and imagery conditions with electroencephalography and multivariate pattern analysis. In a perceptual session we presented of four famous individuals, while in the imagery session we used a cued recall paradigm and presented abstract symbols, associated to them. By using time-resolved multivariate decoding we tested if familiarity information is shared across stimulus categories, and if perceptual face familiarity representations overlap with processing during cued recall, related to imagery. The face perception condition showed typical and robust familiarity information over occipito-temporal electrodes. The symbolic cues also carried similar familiarity information, demonstrating cross-category familiarity processing between symbols and faces. During cued recall, familiarity information emerged over posterior regions and evolved into a prolonged and late information component over right anterior electrodes. Importantly, cross-domain temporal generalization analysis revealed an overlap between perceptual face familiarity patterns and recall/imagery related processing: perceptual face familiarity information mapped onto later processing during cued recall, with a pronounced and prolonged right anterior dominance and a shorter overlap over left posterior channels. Together, these results suggest that familiarity processing, similarly to category representations, is supported by overlapping neural patterns across perception and recall/imagery, transitioning from dynamic posterior representations, consistent with perceptual analysis, to a stable and prolonged representation over right anterior sites, that is compatible with a sustained processing, related to recall and/or imagery.

The external parabrachial nucleus (elPBN) contributes to diverse behaviors, including pain and stress. Neurons in this region use glutamatergic and neuropeptidergic signaling, with pituitary adenylate cyclase-activating polypeptide (PACAP) expressed in a subset of glutamatergic neurons. Deletion of PACAP in elPBN neurons attenuates behavioral responses to stress, but the contribution of PACAP to pain sensitization and of glutamatergic neurotransmission to pain- and stress-related responses remain poorly understood. Here, we show that constitutive loss of PACAP markedly attenuated nerve injury-induced hypersensitivity across heat, pressure, cold and tactile modalities without altering baseline nociception, while also reducing inflammation-induced spontaneous pain-related behavior. Notably, selective deletion of PACAP within elPBN neurons phenocopied the suppression of injury-induced hypersensitivity, but left inflammation- induced pain-related behavior unaffected. Ex vivo optogenetic-assisted circuit mapping showed that activation of PACAP-expressing elPBN terminals elicited glutamatergic transmission onto central amygdala (CeA) PKC{delta}-expressing neurons. Selective deletion of VGluT2 in elPBN neurons reduced nerve injury-induced hypersensitivity but, unlike PACAP deletion, also reduced inflammation-induced pain-related behavior, while leaving stress-induced hypophagia intact. Together, these findings reveal differential requirements for PACAP and glutamatergic neurotransmission within the elPBN across pain- and stress-related behaviors.

The anterolateral system (ALS) originates from neurons in various regions of the spinal cord and conveys somatosensory information related to pain, skin temperature and itch to several brain targets. One component of the ALS is the spinotectal tract, which projects to the superior colliculus (SC) and is thought to underlie directed movements of the head towards a painful stimulus. Using anterograde and retrograde tracing, we demonstrate that the input from the spinal enlargements to the SC originates predominantly from neurons in the lateral spinal nucleus (LSN), many of which express calbindin. This input, which mainly targets the caudal and lateral parts of the SC, is somatotopically organised, and is associated with the clusters of Pitx2-expressing neurons that have been identified in previous studies. Since activation of Pitx2 neurons drives directed head movements, input from LSN neurons to the Pitx2 cells is likely to be a critical component of orientation and attention towards a noxious stimuli. We also provide evidence that spinotectal LSN cells receive excitatory synaptic input from neurons in superficial dorsal horn that express substance P or the gastrin-releasing peptide receptor (GRPR). Since GRPR neurons are strongly implicated in itch, our findings raise the possibility that the SC has a role in coordinating movements in response to pruritic stimuli.