Multiple cortical motor areas and temporal sequencing of movements

Multiple motor areas in the cerebral cortex

Recent accumulation of studies has greatly changed the concept of motor areas in the cerebral cortex of primates 1, 2, 3, 4, 5, 6, 7. In a classical map presented by Woolsey in the l950s 8, 9, only two motor areas are drawn. It is now known, however, that as many as seven somatic motor areas and two oculomotor areas exist in the frontal lobe of primates. Location of these areas in the lateral and mesial parts of the hemisphere is schematically shown in Fig. 1.

In the lateral part, the premotor

Neuronal activity in the SMA is different from that in the MI

Activity properties of neurons in the SMA may appear similar to that in the MI In relation to certain types of movement 45, 46. However, differences in properties of neuronal activity in the two motor areas have been found [47]. Differences can be observed even in simple motor tasks. In simple key-press movements, for instance, onset times of movement-related activity of a majority of MI neurons exhibit correlations with the animal's reaction times. In the SMA, however, only a small number of

A role of SMA in sequential movements

The involvement of the SMA in performance of sequential movements has been suggested in studies on cortical motor potentials [51], in rCBF studies [52], in ablation studies [53], and in studies on SMA-lesioned subjects [54]. However, lesion studies in human subjects and in monkeys revealed the importance of the SMA in the performance of memorized motor acts [55]. Thus, it was necessary to investigate whether or not and how SMA neurons are involved in sequential motor tasks, depending on whether

A role of SMA and pre-SMA in temporal organization of multiple movements

How the nervous system links elementary actions together to organize a variety of meaningful sequences of movements is a question of great interest. To understand roles played by the SMA and pre-SMA in temporal sequencing of multiple movements, we have recently performed a series of experimental studies [58].

We trained two monkeys (Macaca fuscata) to perform three movements (push, pull or turn a manipulandum) in four different orders with their right arm. Monkeys, sitting in a primate chair,