In the external globus pallidus (GPe), a subpopulation of neurons that send projections back to the dorsal striatum is known as arkypallidal (or ‘arky’) neurons. In a study published in Nature Communications, Baker, Kang et al. investigated whether arkypallidal neurons are involved during operant reward-seeking behaviors in mice. Fiber photometric measurements of GPe neurons that project to the dorsolateral striatum (GPe-DLS neurons) showed larger calcium signals during habitual-like reward seeking than during goal-directed responding, and machine learning analyses showed that the calcium signals contained enough information to predict whether a mouse was engaged in habitual or goal-directed behavior. The authors did not further investigate the arkypallidal neurons that project to dorsomedial striatum, which may also participate in value-related behaviors. Interestingly, genetic ablation of the GPe-DLS neurons appeared to promote a shift from goal-directed to habitual responding, whereas their chemogenetic activation caused a global reduction in responding; the latter was prevented by coadministration of a D1 receptor agonist. Taken together, these findings suggest an involvement of the arkypallidal neurons in the regulation of learned reward seeking and contribute another piece to our understanding of the intra-basal ganglia circuitry.
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