Dopamine (DA) is essential for the production of vigorous actions, but how DA modifies the gain of motor commands remains unclear. Here we show that subsecond DA transients in the striatum of mice are neither required nor sufficient for specifying the vigor of ongoing forelimb movements. Our findings have important implications for our understanding of how DA contributes to motor control under physiological conditions and in Parkinson's disease.

Dopaminergic transmission within the ventral striatum is broadly implicated in risk/reward decision making and impulse control, and the rat gambling task (rGT) measures both behaviours concurrently. While the resulting indices of risky choice and impulsivity correlate at the population level, dopaminergic manipulations rarely impact both behaviours uniformly, with changes in choice more likely when dopaminergic transmission is altered during task acquisition. Although the task structure of the rGT remains constant, the relative importance of ventral striatal dopamine signals relevant for reward prediction versus impulse control may vary as learning progresses; the former should dominate while rats learn the probabilistic contingencies of the task, whereas suppression of premature responses becomes more valuable once a decision-making strategy is established and exploited. Striatal cholinergic interneurons (CINs) critically influence reinforcement learning by modulating dopamine release and gating periods of dopamine-facilitated neuroplasticity. We therefore hypothesised that ventral striatal CINs (vsCINs) could influence reward learning or impulse control during task acquisition or stable performance, respectively. Using chemogenetics in Sprague Dawley rats (Rattus norvegicus), we found support for this hypothesis: activation and inhibition of vsCINs once behaviour was stable increased and decreased motor impulsivity in both sexes but had no effect on choice patterns. In contrast, activating and inhibiting vsCINs during task acquisition did not alter motor impulsivity but instead decreased and increased risky choice, respectively. Notably, the former effect was only observed in males, and the latter in females. We conclude by proposing testable predictions regarding acetylcholine-dopamine interactions that may explain sex differences. Impairments in decision making and impulsivity are central to psychiatric conditions such as addiction, ADHD, and impulse control disorders. Understanding how these behaviours are regulated in the brain, and why they differ across individuals and sexes, is critical for developing targeted treatments. This study identifies ventral striatal cholinergic interneurons as important modulators of both impulsivity and risk-based decision making, with their influence depending on learning stage and biological sex. These results show how acetylcholine and dopamine systems interact to shape behaviour in flexible and individualized ways. By revealing circuit-level mechanisms that may underlie sex-specific vulnerabilities and stage-specific treatment outcomes, this work lays the groundwork for more personalized approaches to treating disorders involving poor impulse control and risky decision making.

Research indicates that midbrain dopaminergic neurons encode reward prediction error (RPE) signals involved in positive reinforcement learning. However, studies on dopamine's role in negative reinforcement learning (NRL) are scarce. Learning to escape aversive stimuli is vital for survival and may differ significantly from positive reinforcement in behavior and neural mechanisms. This study employs footshocks as aversive stimuli to investigate neural activity, synaptic transmission, and intrinsic excitability in a NRL paradigm using fiber photometry and ex vivo electrophysiology. Results show that inescapable footshocks initially increase activity in substantia nigra pars compacta (SNc) dopaminergic neurons, which later shifts to reflect shock termination as exposure increases. Electrophysiological observations reveal increased intrinsic excitability and excitatory synaptic transmission in SNc neurons, with decreased inhibitory transmission. After mice learn to escape the shock by nose-poking, dopaminergic activity shifts from shock termination to shock onset. Furthermore, inhibitory input increases, while excitatory input decreases after learning, with intrinsic excitability returning to baseline levels. This indicates that SNc dopaminergic neurons exhibit RPE-like signals in response to aversive stimuli, with their intrinsic excitability adjusting according to expectations of shock termination. These findings enhance our understanding of RPE encoding in negative reinforcement learning and may inform therapeutic strategies for disorders caused by environmental factors such as aversive stimuli.

The substantia nigra pars reticulata (SNr), a key basal ganglia output nucleus, is modulated by dopamine (DA) believed to be released locally from midbrain DA neurons. Although DA has been proposed to regulate γ-aminobutyric acid (GABA) release from medium spiny neuron (MSN) terminals via presynaptic D1 receptors, the precise mechanisms remain unclear. Using presynaptic optical recordings of synaptic vesicle fusion, calcium influx in D1-MSN synapses together with postsynaptic patch-clamp recordings from SNr neurons, we found that DA inhibits D1-MSN GABA release in a frequency-dependent manner. Unexpectedly, this effect was independent of DA receptors and instead required 5-HT1B receptor activation. Using two-photon serotonin biosensor imaging in slices and fiber photometry in vivo, we demonstrate that DA enhances extracellular serotonin in the SNr via inhibition of serotonin reuptake. Our results suggest that serotonin mediates DAergic control of basal ganglia output and contributes to the therapeutic actions of dopaminergic medications for Parkinson's disease and psychostimulant-related disorders.

Active ensembles of neurons form an engram during learning. However, engrams are not immutable, and their organization may change with time via systems consolidation. Here, we labeled engram ensembles in the prelimbic (PrL) cortex during contextual fear conditioning. We found that distinct engram subpopulations ("sub-engrams") contribute to memory recall at recent versus remote delays, with sub-engram contribution determined by their projection profile. At recent delays, sub-engrams projecting to the basal amygdala (BA) and lateral entorhinal cortex (LEC) are activated, and their activity is necessary and sufficient for memory retrieval. At remote delays, sub-engrams projecting to the nucleus reuniens (NRe) and nucleus accumbens (NAc) are additionally recruited, and their activity is necessary and sufficient for memory retrieval. Recruitment of NRe- and NAc-projecting sub-engrams to remote recall is an active process, depending on post-training activation of PrL parvalbumin-expressing interneurons. Post-training chemogenetic inhibition of PrL parvalbumin-expressing interneurons prevented sub-engram recruitment and impaired remote memory.

Previous studies revealed critical involvement of the striatum in adapting to the environment by actions that anticipate rewards from experiences as a policy. However, it remains unclear how current policy is evaluated to explore more advantageous alternatives. Here, we show that during policy-based sequential actions in a rat reversal task, the dorsomedial striatum plays an essential role in pathway-specific manner. Recording and optical manipulation of the indirect pathway showed that late-onset activity following unrewarded suboptimal action represents a lowered valuation of the current action policy and a heightened bias to try the suboptimal action. The early-onset activity complementarily mediated policy-based suppression of unrewarded action. These results demonstrate the indirect pathway's role in monitoring unreliability of current action policy and probing alternative one. This study extends conventional understanding of consequence-guided persistence with reward-oriented action policy and provides key insights regarding how the dorsomedial striatum enables proactive and flexible adaptation to environmental changes.

The striatum plays a central role in motor control, yet how it dynamically represents variables such as locomotion speed, particularly across varying behavioral contexts, remains incompletely understood. Here, we investigated striatal encoding of locomotion speed in rats performing an automated T-maze task. We found that the activity of most (78%) analyzed striatal neurons- referred to as speed cells-was robustly correlated, either positively or negatively, with locomotion speed. This population included both putative medium spiny neurons (MSNs; 74%) and fast-spiking interneurons (FSIs; 82%). Speed-related activity was remarkably stable, showing no significant influence of elapsed time, cue type, spatial choice, or trial outcome. Additionally, positively correlated MSNs tended to precede speed changes, while positively correlated FSI activity typically followed, as did negatively correlated neurons for both types. This suggests distinct roles for different striatal cells in movement modulation. Speed cells exhibited strong modulation at movement onset and offset, yet also maintained correlations with speed throughout locomotion bouts. Finally, the firing rates of speed cells reliably predicted locomotion speed, outperforming non-speed cells and chance levels; decoding accuracy further improved when data from multiple neurons were combined, consistent with a population code. Together, these results demonstrate a robust, context-independent representation of locomotion speed in the rat striatum, driven by diverse cell types, and extends previous findings to a task with greater cognitive demands.

The generation and learning of movements involves interactions among specific neuronal populations within and across brain regions. Important among these regions, for movement among other functions, are the basal ganglia, a set of evolutionarily conserved interconnected deep-brain nuclei. This is strikingly illustrated by how their pathological dysfunction in Parkinson's disease deeply impacts the ability to move. The basal ganglia control the production of different movements through dedicated circuits. These span multiple brain nuclei with complex but highly organized entry and exit routes, from the striatum, the classical input nucleus, to the substantia nigra pars reticulata (SNr), one main output nucleus. Decades of research have focused on understanding the signals that are processed through basal ganglia circuitry and how they contribute to the control of movement. In this primer, we focus on direct interactions between basal ganglia and the brainstem, through which specific populations of basal ganglia output neurons communicate with select brainstem motor centers to influence descending circuits for action. Breakthroughs in understanding brainstem circuits for action execution have made it possible to map the organization and function of the interface between basal ganglia and brainstem. This combined work has led to deep insights into how basal ganglia regulate movement with great granularity.

Many prosocial and antisocial behaviors simultaneously impact both ourselves and others, requiring us to learn from their joint outcomes to guide future choices. However, the neurocomputational processes supporting such social learning remain unclear. Across three pre-registered studies, participants learned how choices affected both themselves and others. Computational modeling tested whether people simulate how other people value their choices or integrate self- and other-relevant information to guide choices. An integrated value framework, rather than simulation, characterizes multi-outcome social learning. People update the expected value of choices using different types of prediction errors related to the target (e.g., self, other) and valence (e.g., positive, negative). This asymmetric value update is represented in brain regions that include ventral striatum, subgenual and pregenual anterior cingulate, insula, and amygdala. These results demonstrate that distinct encoding of self- and other-relevant information guides future social behaviors across mutually beneficial, mutually costly, altruistic, and instrumentally harmful scenarios.

Many genetically encoded voltage indicators (GEVIs) rely on fluorescent protein (FP) domains to report changes in membrane potential. Rapid and reversible disruption of steady-state fluorescence during voltage sensor activation revealed transient conformational changes near the chromophore in the FP domain, implicating chromophore flexibility as a potential mechanism of signal modulation. Substitution of a bulky phenylalanine near the chromophore with threonine (F165T) introduced a distinct secondary component in the fluorescence response, consistent with increased chromophore mobility. This effect was tunable: an external, directionally polarized offset (164/166F) reoriented the internal threonine side chain, restoring steric hindrance and eliminating the secondary signal. Thus, threonine can function as a context-sensitive molecular switch shaped by β-can surface chemistry. A second internal threonine (T203) also acted as a molecular switch under modified external conditions, generating a secondary signal that is susceptible to membrane curvature during depolarization suggesting that plasma membrane geometry can modulate GEVI activity under permissive conformational states. Crystal structures of Super Ecliptic pHluorin (SE), SE A227D, and a new FP variant revealed that external residues can influence internal side chain orientation. In the new variant, pH-dependent rearrangement of the seventh β-strand dramatically repositions D147 from the interior interacting with the chromophore to the external surface, while H148 shifts from the exterior to interact with the chromophore in alkaline conditions. These insights led to the development of a new GEVI, Ulla, which inverts the polarity of the optical signal─becoming brighter upon depolarization─displays reduced pH sensitivity in the physiological range, and performs reliably under low-light, high-speed imaging conditions in vitro and in vivo using widefield and 2-photon microscopy. Together, these findings present a new approach to modulating chromophore behavior offering broad potential for FP-based biosensor development.

Neurons exhibit varying electrophysiological properties due to dynamic changes in spatiotemporal molecular networks. In situ cryo-electron tomography (cryo-ET) provides advantages for high-resolution visualization of macromolecular complexes within their cellular context. Although correlation with fluorescent labeling allows cryo-ET to target specific cellular regions, it does not adequately reflect the electrophysiological properties of heterogeneous neurons. To bridge high-resolution molecular imaging with electrophysiological properties of individual neurons, we develop a Correlative Voltage Imaging and cryo-ET (CoVET) technique. The nondestructive nature of voltage imaging is compatible with cryo-ET, enabling a direct correlation between neuronal electrophysiology and molecular structures. Neurons are clustered based on their electrophysiological properties, allowing for single-cell-guided structural analysis using cryo-ET. We analyze the translational landscapes of individual neurons and find distinct structural characteristics and spatial networks among ribosomes from different electrophysiological clusters. Our results highlight the importance of the correlation between the electrophysiological properties and molecular structures.

The striatal direct and indirect pathways constitute the core for basal ganglia function in action control. Although both striatal D1- and D2-spiny projection neurons (SPNs) receive excitatory inputs from the cerebral cortex, whether or not they share inputs from the same cortical neurons, and how pathway-specific corticostriatal projections control behavior remain largely unknown. Here using a G-deleted rabies system in mice, we found that more than two-thirds of excitatory inputs to D2-SPNs also target D1-SPNs, while only one-third do so vice versa. Optogenetic stimulation of striatal D1- vs. D2-SPN-projecting cortical neurons differently regulate locomotion, reinforcement learning, and sequence behavior, implying the functional dichotomy of pathway-specific corticostriatal subcircuits. These results reveal the partially segregated yet asymmetrically overlapping cortical projections on striatal D1- vs. D2-SPNs, and that the pathway-specific corticostriatal subcircuits distinctly control behavior. It has important implications in a wide range of neurological and psychiatric diseases affecting cortico-basal ganglia circuitry.

The granular retrosplenial cortex (RSG) supports memory, orientation, and fear processing. The mouse RSG contains several cell types that are remarkably distinct from those found in other cortical regions, including low rheobase neurons that dominate layer 2/3 (L2/3 LR) and similarly exclusive pyramidal cells in layer 5a (L5a RSG). While the functions of the RSG are extensively studied in both mice and rats, it remains unknown if the transcriptomically unique cell types of the mouse RSG are evolutionarily conserved in rats. Here, we show that mouse and rat RSG contain the same unique cell types, with L2/3 LR and L5a RSG cell types together representing more than 50% of all RSG neurons in each species. This preservation of cell types in male and female rats happens despite dramatic changes in key cell-type-specific marker genes, with the expression that selectively tags mouse L5a RSG neurons completely absent in rats. Important for Cre-driver line development, we identify alternative, cross-species genes that can be used to selectively target the cell types of the RSG in both mice and rats. Our results show that the unique cell types of the RSG are conserved across millions of years of evolution and emphasize stark species-specific differences in marker genes that need to be considered when making cell-type-specific knock-in lines across species. The retrosplenial cortex is important for memory, spatial orientation, fear processing, and imagining oneself in the future. Lesions to this brain region in humans lead to an inability to find one's way home. The mouse granular retrosplenial cortex (RSG) contains neuron types that are particularly distinct from those found in neighboring regions. Whether these distinct neurons are preserved across species remains unknown. Here, we show that all cell types of the mouse RSG are also found in rats, and the unique RSG cell types dominate the region in each species. These results suggest that the unique RSG neurons support evolutionarily important functions that facilitate the preservation of these neurons across millions of years of evolution.

Acetylcholine (ACh) plays important roles in memory encoding and attention in the hippocampus. However, changes in ACh signaling patterns during different neural and behavioral states remain poorly understood. Here, we used a genetically encoded ACh sensor and multi-plane, dual-color two-photon microscopy to establish the ACh signaling patterns in hippocampal CA1 of mice performing spatial behaviors. We observed spatially homogeneous signaling across volumes spanning hundreds of microns, which was positively correlated with locomotion speed. In novel environments, there was an increase in release persisting for dozens of laps while maintaining a positive speed correlation. When mice voluntarily disengaged, the magnitude of the speed-correlated release decreased, and this was accompanied by reduced place cell numbers and less precise place maps. Administration of scopolamine mimicked the effects of voluntary disengagement in terms of behavior and place cell metrics. These findings establish behaviorally correlated ACh signaling patterns in the hippocampus.

Models of visual salience detection rely on center-surround interactions, yet it remains unclear how these computations are distributed across retinal, cortical, and subcortical circuits due to their overlapping contributions. Here, we reveal a de novo collicular mechanism for surround suppression by combining patterned optogenetics with whole-cell recordings from individual neurons in the mouse superficial superior colliculus (SCs). Center zones were defined by monosynaptic input from channelrhodopsin-expressing retinal ganglion cells in collicular midbrain slices. Surround network optoactivation suppressed center responses compared to center-only input. This suppression is excitatory in origin, arising from the withdrawal of center excitation via surround-driven inhibition of local recurrent excitatory circuits, as demonstrated by cell-type-specific trans-synaptic tracing and computational modeling. These findings identify a local circuit mechanism for saliency computation in the SCs, independent of cortical input.

To navigate dynamic environments, animals must rapidly integrate sensory information and respond appropriately to gather rewards and avoid threats. It is well established that dopamine (DA) neurons in the ventral tegmental area (VTA) and substantia nigra (SNc) are key for creating associations between environmental stimuli (i.e., cues) and the outcomes they predict. Critically, it remains unclear how sensory information is integrated into dopamine pathways. The superior colliculus (SC) receives direct visual input and is positioned as a relay for dopamine neuron augmentation. We characterized the anatomy and functional impact of SC projections to the VTA/SNc in male and female rats. First, we show that neurons in the deep layers of SC synapse densely throughout the ventral midbrain, interfacing with projections to the striatum and ventral pallidum, and these SC projections excite dopamine and GABA neurons in the VTA/SNc in vivo. Despite this, cues predicting SC→VTA/SNc neuron activation did not reliably evoke behavior in an optogenetic Pavlovian conditioning paradigm, and activation of SC→VTA/SNc neurons did not support primary reinforcement or produce place preference/avoidance. Instead, we find that stimulation of SC→VTA/SNc neurons evokes head turning. Focusing optogenetic activation solely onto dopamine neurons that receive input from the SC was sufficient to invigorate turning, but not reinforcement. Turning intensity increased with repeated stimulations, suggesting that this circuit may underlie sensorimotor learning for exploration and attentional switching. Together, our results show that collicular neurons contribute to cue-guided behaviors by controlling pose adjustments through interaction with dopamine neurons that preferentially engage movement instead of reward. In dynamic environments, animals must rapidly integrate sensory information and respond appropriately to survive. Dopamine (DA) neurons are key for creating associations between environmental cues through learning, but it remains unclear how relevant sensory information is integrated into DA pathways to guide this process. The superior colliculus (SC) is positioned for rapid sensory augmentation of dopamine neurons. Using a combination of approaches, we find that SC neurons projecting to the ventral midbrain activate dopamine neurons and drive postural changes without creating conditioned behavior or valence. Our results highlight a brain circuit that is important for guiding movement to redirect attention, via interaction with classic learning systems, and suggest distinct subpopulations of dopamine neurons preferentially engage movement instead of reward.

Synchronous neuronal ensembles play a pivotal role in the consolidation of long-term memory in the hippocampus. However, their organization during the acquisition of spatial memory remains less clear. In this study, we used neuronal population voltage imaging to investigate the synchronization patterns of mice CA1 pyramidal neuronal ensembles during the exploration of a new environment, a critical phase for spatial memory acquisition. We found synchronous ensembles comprising approximately 40% of CA1 pyramidal neurons, firing simultaneously in brief windows (~25ms) during immobility and locomotion in novel exploration. Notably, these synchronous ensembles were not associated with contralateral ripple oscillations but were instead phase-locked to theta waves recorded in the contralateral CA1 region. Moreover, the subthreshold membrane potentials of neurons exhibited coherent intracellular theta oscillations with a depolarizing peak at the moment of synchrony. Among newly formed place cells, pairs with more robust synchronization during locomotion displayed more distinct place-specific activities. These findings underscore the role of synchronous ensembles in coordinating place cells of different place fields.

Foraging and food consumption are fundamental for the survival of animals. In natural environments, wild rodents feed on insects, including moth larvae, and odor-guided evaluation of potential food resources is a critical step in initiating feeding behavior. However, the mechanisms by which rodents seek and feed on insect prey remain poorly understood. Herein, we employed a laboratory-based predator-prey interaction system using mice and cotton bollworm larvae to investigate the neural mechanisms underlying food-seeking and feeding behaviors at both cellular and neural circuit levels. We demonstrate that mice exhibit a strong preference for consuming fed larvae, and this preference is dependent on the main olfactory system. Gas chromatography-mass spectrometry analysis revealed significant differences in the chemical profiles of fed and unfed larvae, with fed larvae containing a higher level of linoleic acid (LA) and a lower level of (Z)-9-tricosene [(Z)-9-TE]. Behavioral assays showed that mice, as well as Brand's voles and brown rats, are attracted to LA but avoid (Z)-9-TE in a two-choice odor preference test. Furthermore, we identified that the dopaminergic pathway from the ventral tegmental area (VTA) to the medial olfactory tubercle (mOT) plays a central role in mediating this preference. Chemogenetic inhibition of this pathway abolished the preference for LA over (Z)-9-TE, while chemogenetic activation reversed this effect. Additionally, fiber photometry recordings and pharmacology revealed that mOT D1 and D2 spiny projection neurons preferentially mediate attraction to LA and avoidance of (Z)-9-TE, respectively. These findings uncover a neurobiological system in rodents that supports insect predation based upon chemosignals.