Multiplexed action-outcome representation by striatal striosome-matrix compartments detected with a mouse cost-benefit foraging task

Medial prefrontal cortex suppresses reward-seeking behavior with risk of punishment by reducing sensitivity to reward

Reward-seeking behavior is frequently associated with risk of punishment. There are two types of punishment: positive punishment, which is defined as addition of an aversive stimulus, and negative punishment, involves the omission of a rewarding outcome. Although the medial prefrontal cortex (mPFC) is important in avoiding punishment, whether it is important for avoiding both positive and negative punishment and how it contributes to such avoidance are not clear. In this study, we trained male mice to perform decision-making tasks under the risks of positive (air-puff stimulus) and negative (reward omission) punishment, and modeled their behavior with reinforcement learning. Following the training, we pharmacologically inhibited the mPFC. We found that pharmacological inactivation of mPFC enhanced the reward-seeking choice under the risk of positive, but not negative, punishment. In reinforcement learning models, this behavioral change was well-explained as an increase in sensitivity to reward, rather than a decrease in the strength of aversion to punishment. Our results suggest that mPFC suppresses reward-seeking behavior by reducing sensitivity to reward under the risk of positive punishment.

Developmental and adult striatal patterning of nociceptin ligand marks striosomal population with direct dopamine projections

Circuit influences on the midbrain dopamine system are crucial to adaptive behavior and cognition. Recent developments in the study of neuropeptide systems have enabled high-resolution investigations of the intersection of neuromodulatory signals with basal ganglia circuitry, identifying the nociceptin/orphanin FQ (N/OFQ) endogenous opioid peptide system as a prospective regulator of striatal dopamine signaling. Using a prepronociceptin-Cre reporter mouse line, we characterized highly selective striosomal patterning of Pnoc mRNA expression in mouse dorsal striatum, reflecting early developmental expression of Pnoc . In the ventral striatum, Pnoc expression was was clustered across the nucleus accumbens core and medial shell, including in adult striatum. We found that Pnoc tdTomato reporter cells largely comprise a population of dopamine receptor D1 ( Drd1 ) expressing medium spiny projection neurons localized in dorsal striosomes, known to be unique among striatal projections neurons for their direct innervation of midbrain dopamine neurons. These findings provide new understanding of the intersection of the N/OFQ system among basal ganglia circuits with particular implications for developmental regulation or wiring of striatal-nigral circuits.

In humans, insulo-striate structural connectivity is largely biased toward either striosome-like or matrix-like striatal compartments

The insula is an integral component of sensory, motor, limbic, and executive functions, and insular dysfunction is associated with numerous human neuropsychiatric disorders. Insular afferents project widely, but insulo-striate projections are especially numerous. The targets of these insulo-striate projections are organized into tissue compartments, the striosome and matrix. These striatal compartments have distinct embryologic origins, afferent and efferent connectivity, dopamine pharmacology, and susceptibility to injury. Striosome and matrix appear to occupy separate sets of cortico-striato-thalamo-cortical loops, so a bias in insulo-striate projections towards one compartment may also embed an insular subregion in distinct regulatory and functional networks. Compartment-specific mapping of insulo-striate structural connectivity is sparse; the insular subregions are largely unmapped for compartment-specific projections. In 100 healthy adults, we utilized probabilistic diffusion tractography to map and quantify structural connectivity between 19 structurally-defined insular subregions and each striatal compartment. Insulo-striate streamlines that reached striosome-like and matrix-like voxels were concentrated in distinct insular zones (striosome: rostro- and caudoventral; matrix: caudodorsal) and followed different paths to reach the striatum. Though tractography was generated independently in each hemisphere, the spatial distribution and relative bias of striosome-like and matrix-like streamlines were highly similar in the left and right insula. 16 insular subregions were significantly biased towards one compartment: seven toward striosome-like voxels and nine toward matrix-like voxels. Striosome-favoring bundles had significantly higher streamline density, especially from rostroventral insular subregions. The biases in insulo-striate structural connectivity we identified mirrored the compartment-specific biases identified in prior studies that utilized injected tract tracers, cytoarchitecture, or functional MRI. Segregating insulo-striate structural connectivity through either striosome or matrix may be an anatomic substrate for functional specialization among the insular subregions.

Chronic Ethanol Exposure Produces Persistent Impairment in Cognitive Flexibility and Decision Signals in the Striatum

Lack of cognitive flexibility is a hallmark of substance use disorders and has been associated with drug-induced synaptic plasticity in the dorsomedial striatum (DMS). Yet the possible impact of altered plasticity on real-time striatal neural dynamics during decision-making is unclear. Here, we identified persistent impairments induced by chronic ethanol (EtOH) exposure on cognitive flexibility and striatal decision signals. After a substantial withdrawal period from prior EtOH vapor exposure, male, but not female, rats exhibited reduced adaptability and exploratory behavior during a dynamic decision-making task. Reinforcement learning models showed that prior EtOH exposure enhanced learning from rewards over omissions. Notably, neural signals in the DMS related to the decision outcome were enhanced, while those related to choice and choice-outcome conjunction were reduced, in EtOH-treated rats compared to the controls. These findings highlight the profound impact of chronic EtOH exposure on adaptive decision-making, pinpointing specific changes in striatal representations of actions and outcomes as underlying mechanisms for cognitive deficits.

D1 and D2 medium spiny neurons in the nucleus accumbens core have distinct and valence-independent roles in learning

At the core of value-based learning is the nucleus accumbens (NAc). D1- and D2-receptor-containing medium spiny neurons (MSNs) in the NAc core are hypothesized to have opposing valence-based roles in behavior. Using optical imaging and manipulation approaches in mice, we show that neither D1 nor D2 MSNs signal valence. D1 MSN responses were evoked by stimuli regardless of valence or contingency. D2 MSNs were evoked by both cues and outcomes, were dynamically changed with learning, and tracked valence-free prediction error at the population and individual neuron level. Finally, D2 MSN responses to cues were necessary for associative learning. Thus, D1 and D2 MSNs work in tandem, rather than in opposition, by signaling specific properties of stimuli to control learning.

In humans, striato-pallido-thalamic projections are largely segregated by their origin in either the striosome-like or matrix-like compartments

Cortico-striato-thalamo-cortical (CSTC) loops are fundamental organizing units in mammalian brains. CSTCs process limbic, associative, and sensorimotor information in largely separated but interacting networks. CTSC loops pass through paired striatal compartments, striosome (aka patch) and matrix, segregated pools of medium spiny projection neurons with distinct embryologic origins, cortical/subcortical structural connectivity, susceptibility to injury, and roles in behaviors and diseases. Similarly, striatal dopamine modulates activity in striosome and matrix in opposite directions. Routing CSTCs through one compartment may be an anatomical basis for regulating discrete functions. We used differential structural connectivity, identified through probabilistic diffusion tractography, to distinguish the striatal compartments (striosome-like and matrix-like voxels) in living humans. We then mapped compartment-specific projections and quantified structural connectivity between each striatal compartment, the globus pallidus interna (GPi), and 20 thalamic nuclei in 221 healthy adults. We found that striosome-originating and matrix-originating streamlines were segregated within the GPi: striosome-like connectivity was significantly more rostral, ventral, and medial. Striato-pallido-thalamic streamline bundles that were seeded from striosome-like and matrix-like voxels transited spatially distinct portions of the white matter. Matrix-like streamlines were 5.7-fold more likely to reach the GPi, replicating animal tract-tracing studies. Striosome-like connectivity dominated in six thalamic nuclei (anteroventral, central lateral, laterodorsal, lateral posterior, mediodorsal-medial, and medial geniculate). Matrix-like connectivity dominated in seven thalamic nuclei (centromedian, parafascicular, pulvinar-anterior, pulvinar-lateral, ventral lateral-anterior, ventral lateral-posterior, ventral posterolateral). Though we mapped all thalamic nuclei independently, functionally-related nuclei were matched for compartment-level bias. We validated these results with prior thalamostriate tract tracing studies in non-human primates and other species; where reliable data was available, all agreed with our measures of structural connectivity. Matrix-like connectivity was lateralized (left > right hemisphere) in 18 thalamic nuclei, independent of handedness, diffusion protocol, sex, or whether the nucleus was striosome-dominated or matrix-dominated. Compartment-specific biases in striato-pallido-thalamic structural connectivity suggest that routing CSTC loops through striosome-like or matrix-like voxels is a fundamental mechanism for organizing and regulating brain networks. Our MRI-based assessments of striato-thalamic connectivity in humans match and extend the results of prior tract tracing studies in animals. Compartment-level characterization may improve localization of human neuropathologies and improve neurosurgical targeting in the GPi and thalamus.

An open-source platform for head-fixed operant and consummatory behavior

Head-fixed behavioral experiments in rodents permit unparalleled experimental control, precise measurement of behavior, and concurrent modulation and measurement of neural activity. Here, we present OHRBETS (Open-Source Head-fixed Rodent Behavioral Experimental Training System; pronounced 'Orbitz'), a low-cost, open-source platform of hardware and software to flexibly pursue the neural basis of a variety of motivated behaviors. Head-fixed mice tested with OHRBETS displayed operant conditioning for caloric reward that replicates core behavioral phenotypes observed during freely moving conditions. OHRBETS also permits optogenetic intracranial self-stimulation under positive or negative operant conditioning procedures and real-time place preference behavior, like that observed in freely moving assays. In a multi-spout brief-access consumption task, mice displayed licking as a function of concentration of sucrose, quinine, and sodium chloride, with licking modulated by homeostatic or circadian influences. Finally, to highlight the functionality of OHRBETS, we measured mesolimbic dopamine signals during the multi-spout brief-access task that display strong correlations with relative solution value and magnitude of consumption. All designs, programs, and instructions are provided freely online. This customizable platform enables replicable operant and consummatory behaviors and can be incorporated with methods to perturb and record neural dynamics in vivo.

Striosomes and Matrisomes: Scaffolds for Dynamic Coupling of Volition and Action

Striosomes form neurochemically specialized compartments of the striatum embedded in a large matrix made up of modules called matrisomes. Striosome-matrix architecture is multiplexed with the canonical direct-indirect organization of the striatum. Striosomal functions remain to be fully clarified, but key information is emerging. First, striosomes powerfully innervate nigral dopamine-containing neurons and can completely shut down their activity, with a following rebound excitation. Second, striosomes receive limbic and cognition-related corticostriatal afferents and are dynamically modulated in relation to value-based actions. Third, striosomes are spatially interspersed among matrisomes and interneurons and are influenced by local and global neuromodulatory and oscillatory activities. Fourth, striosomes tune engagement and the motivation to perform reinforcement learning, to manifest stereotypical behaviors, and to navigate valence conflicts and valence discriminations. We suggest that, at an algorithmic level, striosomes could serve as distributed scaffolds to provide formats of the striatal computations generated through development and refined through learning. We propose that striosomes affect subjective states. By transforming corticothalamic and other inputs to the functional formats of the striatum, they could implement state transitions in nigro-striato-nigral circuits to affect bodily and cognitive actions according to internal motives whose functions are compromised in neuropsychiatric conditions.

A neural substrate of sex-dependent modulation of motivation

While there is emerging evidence of sex differences in decision-making behavior, the neural substrates that underlie such differences remain largely unknown. Here we demonstrate that in mice performing a value-based decision-making task, while choices are similar between the sexes, motivation to engage in the task is modulated by action value more strongly in females than in males. Inhibition of activity in anterior cingulate cortex (ACC) neurons that project to the dorsomedial striatum (DMS) preferentially disrupts this relationship between value and motivation in females, without affecting choice in either sex. In line with these effects, in females compared to males, ACC-DMS neurons have stronger representations of negative outcomes and more neurons are active when the value of the chosen option is low. By contrast, the representation of each choice is similar between the sexes. Thus, we identify a neural substrate that contributes to sex-specific modulation of motivation by value.

An Open-Source Platform for Head-Fixed Operant and Consummatory Behavior

Head-fixed behavioral experiments in rodents permit unparalleled experimental control, precise measurement of behavior, and concurrent modulation and measurement of neural activity. Here we present OHRBETS (Open-Source Head-fixed Rodent Behavioral Experimental Training System; pronounced 'Orbitz'), a low-cost, open-source ecosystem of hardware and software to flexibly pursue the neural basis of a variety of motivated behaviors. Head-fixed mice tested with OHRBETS displayed operant conditioning for caloric reward that replicates core behavioral phenotypes observed during freely moving conditions. OHRBETS also permits for optogenetic intracranial self-stimulation under positive or negative operant conditioning procedures and real-time place preference behavior, like that observed in freely moving assays. In a multi-spout brief-access consumption task, mice displayed licking as a function of concentration of sucrose, quinine, and sodium chloride, with licking modulated by homeostatic or circadian influences. Finally, to highlight the functionality of OHRBETS, we measured mesolimbic dopamine signals during the multi-spout brief-access task that display strong correlations with relative solution value and magnitude of consumption. All designs, programs, and instructions are provided freely online. This customizable ecosystem enables replicable operant and consummatory behaviors and can be incorporated with methods to perturb and record neural dynamics in vivo .

Impact Statement

A customizable open-source hardware and software ecosystem for conducting diverse head-fixed behavioral experiments in mice.

Direct cerebello-striatal loop in dystonia as a possible new target for deep brain stimulation: A revised view of subcortical pathways involved

Dystonia is the second most common movement disorder next to tremor, but its pathophysiology remains unsettled. Its therapeutic measures include anti-cholingerics and other medications, in addition to botulinum neurotoxin injections, and stereotaxic surgery including deep brain stimulation (DBS), but there still remain a number of patients resistant to the therapy. Evidence has been accumulating suggesting that basal ganglia in association with the cerebellum are playing a pivotal role in pathogenesis. Clinical observations such as sensory tricks and the effects of muscle afferent stimulation and blockage suggest the conflict between the cortical voluntary motor plan and the subcortical motor program or motor subroutine controlling the intended action semi-automatically. In this review, the current understanding of the possible pathways or loops involved in dystonia is presented, and we review promising new targets for Deep Brain Stimulation (DBS) including the cerebellum.