Role of rodent secondary motor cortex in value-based action selection

The authors examined neuronal activity in the lateral (AGl) and medial (AGm) agranular cortex, corresponding to the primary and secondary motor cortex, respectively, in rats performing a dynamic foraging task. They find that rodent secondary motor cortex might be uniquely involved in both representing and reading out value signals for flexible action selection. Despite widespread neural activity related to reward values, signals related to upcoming choice have not been clearly identified in the rodent brain. Here we examined neuronal activity in the lateral (AGl) and medial (AGm) agranular cortex, corresponding to the primary and secondary motor cortex, respectively, in rats performing a dynamic foraging task. Choice signals, before behavioral manifestation of the rat's choice, arose in the AGm earlier than in any other areas of the rat brain previously studied under free-choice conditions. The AGm also conveyed neural signals for decision value and chosen value. By contrast, upcoming choice signals arose later, and value signals were weaker, in the AGl. We also found that AGm lesions made the rats' choices less dependent on dynamically updated values. These results suggest that rodent secondary motor cortex might be uniquely involved in both representing and reading out value signals for flexible action selection.