Mediodorsal thalamic input to striatum contributes to early action learning

Action control is hypothesized to be mediated by corticothalamo-basal ganglia loops subserving the acquisition and updating of action contingencies. Within this, the mediodorsal thalamus (MD) is thought to contribute to volitional control over behavior largely through its interactions with prefrontal cortex. However, MD also projects into striatum, the main input nucleus of the basal ganglia, and the contribution of such projections to behavioral control is not known. Using a mouse model of volitional action control in either sex, here we find that MD terminal calcium activity in dorsal medial striatum (MD-DMS) represents action information during initial acquisition of a novel action contingency. This representation of action information decreases with continued experience. Data demonstrate MD-DMS activity is necessary to learn and employ a contingency control over actions. Functional attenuation of MD-DMS activity negated normal exploration, instead biasing repetitive action control, and resulted in mice unable to adapt their initial action strategy upon changes in action contingency. This suggests MD supports plasticity underlying initial action strategy learning used to adjust control given changing contingencies. Overall, these data show that MD projections into striatum contribute to volitional action control that supports acquisition of adaptive behavior. Significance Statement Mediodorsal (MD) thalamus is hypothesized to support volitional action control. However, focus has largely been on MD input into prefrontal cortical regions and the contribution of MD input to striatum has not been explored. Here we show that MD input into dorsal medial striatum supports acquisition of goal-directed strategies and their control over actions.