[Comparison of triggered movement-related and self paced movement-related neuronal activities in the frontal...

To examine the functional differences in primate motor cortex (MC), premotor cortex (PM) and supplementary motor area (SMA), single cell activities in these areas were recorded from monkeys performing either visually triggered or self paced key press movement. EMG recordings made clear that activities in finger and hand flexor muscles preceding the triggered or self paced movement were identical and no limb and body muscles were active during performing the task. Neuronal activity changes preceding movement onsets were classified into two categories; a short lead type with the preceding time of less than 300 ms, a long lead type with longer preceding times. In MC, a majority of movement-related neurons (86%) was active phasically and therefore belonged to a short lead type. They exhibited similar activity changes regardless of whether triggered or self paced. In PM, 87% of movement-related neurons were of short lead type. About one third of them were triggered movement specific and another one third were triggered movement predominant. These preferential relation to triggered movement were characteristic in PM. Neurons of SMA were different from MC and PM cells in that as much as a half of them showed the long lead type of activity changes and almost all of these cells were classified into self paced movement dominant or specific. These results suggest that each of these areas have different functional characteristics. PM has more preferential relation to the triggered movement and SMA has more preferential relation to the self paced movement, whereas MC is involved equally in both.