Spatio-temporal dynamics of sensorimotor transformations in mouse dorsal cortex

To make decisions and produce actions, animals must make judgements about the state of the world based on prior knowledge and current sensory input. In order to probe neural circuits underlying such sensorimotor transformations, we developed a behavioural task in which stationary mice had to detect a sustained increase in the speed of a continuously varying visual stimulus, while we manipulated the animals’ expectation of when changes were probable. The design of the task allowed us to temporally separate processes that occur when the mouse reaches and executes its choice from processes that occur while the belief state of the mouse is still influenced by noisy sensory evidence. We then used wide-field calcium imaging to identify neural correlates of these processes in the dorsal neocortex.
We found only a subset of cortical areas was modulated by the visual stimulus during the deliberation period while global responses were observed around choice execution and other overt movements. In visual cortical areas, stimulus responses were short-lived and independent of task experience. In contrast, responses in secondary motor cortex were selective for increases in stimulus speed, persisted beyond stimulus presentation, were influenced by animals’ expectation of the stimulus change, and occurred only in trained animals. These results suggest that secondary motor cortex plays a key role not only in motor preparation and execution of choice, but also during the continuous evaluation of sensory evidence during perceptual decision-making.