HIGH OR LOW LEVEL FUNCTION OF STRIATUM? INSIGHTS FROM UNILATERAL PERTURBATIONS IN A NEW NATURALISTIC FORAGING TASK FOR FREELY MOVING MICE

The dorsal striatum has been proposed to contribute to action selection and/or to the moment-to-moment control of movement kinematics. Yet, unilateral perturbations of striatal projection neurons expressing D1 (dSPNs) or D2 (iSPNs) receptors induce contralateral or ipsilateral movements, respectively, raising the unresolved question of whether these effects reflect biased action selection, altered movement execution, or a combination of both. To probe this issue, we developed a new task in which mice must perform leftward or rightward rotations to obtain rewards. We hypothesized that if perturbation-induced rotations align with the currently rewarded direction, performance should be facilitated, whereas incongruent perturbations should impair performance. We designed the “Towers Foraging Park,” a freely moving foraging task set in a large square arena containing four square towers around which mice must rotate to obtain rewards. To compare congruent and incongruent conditions within the same subjects, the rewarded turning direction alternates across days, allowing each mouse to experience both perturbation contexts. Results show that unilateral perturbations targeting either dSPNs or iSPNs significantly reduce the number of turns and turning speed, regardless of congruency. Unexpectedly, only congruent perturbations reduce the fraction of successful turns. We hypothesize that this effect could arise from a larger motor cost in the congruent condition, due to body orientation constraints imposed by the square tower geometry. These results suggest that the dorsal striatum may contribute to setting up a motor cost that influences both action choices and movement kinematics under specific task constraints.