Neuronal activity in the supplementary and presupplementary motor areas for temporal organization of multiple movements

To study how neurons in the medial motor areas participate in performing se quential multiple movements that are individually separated in time, we ana lyzed neuronal activity in the supplementary (SMA) and pre-supplementary (p re-SMA) motor areas. Monkeys were trained to perform three different moveme nts separated by waiting times, in four or six different orders. Initially each series of movements was learned during five trials guided by visual si gnals that indicated the correct movements. The monkeys subsequently execut ed the three movements in the memorized order without the visual signals. T hree types of neuronal activity were of particular interest; these appeared to be crucially involved in sequencing the multiple motor tasks in differe nt orders. First, we found activity changes that were selective for a parti cular sequence of the three movements that the monkeys were prepared to per form. The sequence-selective activity ceased when the monkeys initiated the first movement. Second, we found interval-selective activity that appeared in the interval between one particular movement and the next. Third, we fo und neuronal activity representing the rank order of three movements arrang ed chronologically; that is, the activity differed selectively in the proce ss of preparing the first, second, or third movements in individual trials. The interval-selective activity was more prevalent in the SMA, whereas the rank-order selective activity was more frequently recorded in the pre-SMA. These results suggest how neurons in the SMA and pre-SMA are involved in s equencing multiple movements over time.