Differential motor neuron activity in rats during successful and failed grasping.

A substantial body of literature has focused on neural signals evoked by errors emerging during the execution of goal-directed actions. It is still unclear how motor cortex activity during movement execution relates to feedback error processing. To investigate this, we recorded primary motor cortex (M1) single-unit activity in rats during a grasping task. About half of the recorded neurons showed modulation of their firing activity that did not depend on success or failure, which we termed outcome-independent neurons. Other neurons showed a difference in their discharge profile when comparing successful and unsuccessful trials, which we called outcome-dependent neurons. Among both outcome-dependent and -independent neurons, we further distinguished neurons presenting their maximum firing rate in specific epochs as defined by the task. We compared the cortical distribution of outcome-independent and outcome-dependent neurons to cortical maps of complex forelimb movements evoked by intracortical microstimulation in additional animals. The majority of outcome-independent neurons was localized within the limb extension and paw open-closure movement representations. Outcome-dependent neurons were not clearly associated to particular motor representations. Cortical arrangement of neurons, both outcome-independent and outcome-dependent, and their correlation with distinct movement representations, can serve as indicator for anticipating potential outcomes before the conclusion of an action.