Final answer:
The premotor and supplemental motor areas are aspects of the brain's motor system responsible for planning and initiating movement sequences based on learned experiences, which leads up to actions taken by the primary motor cortex.
Step-by-step explanation:
The premotor cortex and the supplemental motor area are secondary motor cortices involved in planning, coordinating, and executing movements. These areas manage sequential movements that are based on prior experience—learned movements. The neurons in these regions are most active leading up to the initiation of movement, preparing the body for actions like driving in anticipation of a traffic light change. The primary motor cortex is arranged topographically with a motor homunculus, where different body parts are controlled by specific parts of the cortex. The motor responses are generated by large Betz cells projecting through the corticobulbar and corticospinal tracts to synapse on lower motor neurons in the brainstem and spinal cord.
The information you provided indicates that activity in the premotor and motor cortex could reflect the position of an action within a sequence of actions, likely due to their role in movement planning and coordination. The conscious perception of initiating movement is managed by the primary motor cortex, which sends descending commands to the brainstem or spinal cord.