PARVALBUMIN INTERNEURONS WITHIN THE POSTERIOR DORSOMEDIAL STRIATUM REGULATE UPDATING OF ACTION–OUTCOME ASSOCIATIONS DURING REVERSAL LEARNING

Cognitive flexibility requires the ability to update previously learned action–outcome associations when contingencies change. The posterior dorsomedial striatum (pDMS) plays a central role in this process, yet the contribution of parvalbumin-positive fast-spiking interneurons (PV interneurons), which provide strong feedforward inhibition within this region, has not been directly tested. Here, we examined whether activating PV interneurons alters the acquisition or updating of goal-directed actions. Rats were trained on two distinct action–outcome contingencies using pellet and sucrose outcomes and were subsequently assessed with outcome-specific devaluation tests conducted drug-free. Using chemogenetics, we selectively stimulated activity of PV interneurons during initial training. The drug-free test revealed that PV-interneuron activation did not affect initial learning; both stimulated and control groups showed intact outcome devaluation. We then reversed the action–outcome contingencies across additional reversal training sessions, again under PV stimulation. The drug-free test revealed that PV-interneuron activation produced a clear impairment in reversal learning. Although both groups increased responding across training days, only control rats showed a devaluation effect after reversal. Reinforced and reinstatement tests were normal across groups, indicating preserved motivation and motor control. These results demonstrate that increased activity of PV interneurons in the pDMS does not impair initial action–outcome associations but selectively disrupts their updating when contingencies reverse, identifying PV interneurons as a key inhibitory element contributing to cognitive flexibility during reversal learning