Cooperative structures for visually guided reach.

In this introductory commentary, it is argued that the many areas in the cerebral cortex, cerebellum, and elsewhere that are active during reaching movements must interact to generate the appropriate neuronal drive for any given reach trajectory. Cooperative interaction among dispersed neuronal groups may be facilitated by synchronization of intrinsic oscillatory cycles of excitability. In sensorimotor cortex, intervals of oscillatory activity in relatively high frequency bands have been linked to the preparation phase of limb movements. Moreover, synchronization of oscillatory cycles in different loci of frontal and parietal cortex has been reported. Oscillation frequencies change abruptly at the onset of movement, which could reflect altered cerebellar influences on motor thalamocortical circuits. Since relaxation coupling within the thalamus is a probable mechanism of cortical synchronization, it is postulated that cerebellar output contributes to synchronization patterns.