Differential formation of motor cortical dynamics during movement preparation according to the predictability of go timing

Abstract

Motor cortex not only executes but also prepares movement, as motor cortical neurons exhibit preparatory activity that predicts upcoming movements. In movement preparation, animals adopt different strategies in response to uncertainties existing in nature such as the unknown timing of when a predator will attack--an environmental cue informing go. However, how motor cortical neurons cope with such uncertainties is less understood. In this study, we aim to investigate whether and how preparatory activity is altered depending on the predictability of go timing. We analyze firing activities of anterior lateral motor cortex (ALM) in mice during two auditory delayed-response tasks each with predictable or unpredictable go timing. When go timing is unpredictable, preparatory activities immediately reach and stay in a neural state capable of producing movement anytime to a sudden go cue. When go timing is predictable, preparation activity reaches the movement-producible state more gradually, to secure more accurate decisions. Surprisingly, this preparation process entails a longer reaction time (RT). We find that as preparatory activity increase in accuracy, it takes longer for a neural state to transition from the end of preparation to the start of movement. Our results suggest that motor cortex fine-tunes preparatory activity for more accurate movement using the predictability of go timing. Significant statementsAnticipating when to move is important in movement preparation. However, it is unclear how motor cortex prepares movement depending on how easy that anticipation is. To answer this, we examine motor cortical activity of mice during a delayed-response task. While motor cortical activity rapidly reaches a "movement-ready" state with unpredictable timing of a go signal (go timing), it does so more gradually when go timing is predictable. Moreover, when go timing is more predictable, motor cortex produces more accurate movement with, unexpectedly, a longer response time. This suggests that rodent motor cortical neurons can resource time information.