Previous research has focused on the anterior cingulate cortex (ACC) as a key brain region in the mitigation of the competition that arises from two simultaneously active signals. However, to date, no study has demonstrated that ACC is necessary for this form of behavioral flexibility, nor have any studies shown that ACC acts by modulating downstream brain regions such as the dorsal medial striatum (DMS) that encode action plans necessary for task completion. Here, we performed unilateral excitotoxic lesions of ACC while recording downstream from the ipsilateral hemisphere of DMS in rats, performing a variant of the STOP-signal task. We show that on STOP trials lesioned rats perform worse, in part due to the failure of timely directional action plans to emerge in the DMS, as well as the overrepresentation of the to-be-inhibited behavior. Collectively, our findings suggest that ACC is necessary for the mitigation of competing inputs and validates many of the existing theoretical predictions for the role of ACC in cognitive control.
