Neuronal activity in the primate non-primary cortex is different from that in the primary motor cortex

This paper describes differences in the properties of single-cell activity in the primary and non-primary motor cortex of behaving monkeys (Macaca fuscata). New findings were obtained in relation to two different behavioural paradigms. First, we found that a large number of non-primary motor cortex neurons exhibit selective or preferential relationships to either signal-triggered or self-paced movement. In the second series of experiments, monkeys were trained to press a small key with the right or left hand, or with both hands. Most primary motor cortex neurons behaved like muscles in the contralateral hand. In contrast, a number of non-primary motor cortex neurons exhibited a selective relationship to the movement (right or left key press, or bilateral key press). The differences suggest the different roles of these two areas in motor control. Studies of this sort seem to start providing answers to the old question of why the non-primary motor cortex exists.