The liaison brain for voluntary movement: the supplementary motor area.

An account of the origin of the term liaison brain leads on to an historical account of its usage, particularly in voluntary movement. Empirical evidence was provided by the readiness potential of Kornhuber and associates, which even indicated a key role for the supplementary motor area, SMA. It was found by Brinkman and Porter that in voluntary movement many neurones of the SMA were activated probably up to 200 msec before the pyramidal tract discharge. Then came the (133)Xe investigations of regional cerebral blood flow by Roland and associates to reveal that there was neuronal activity in the SMA of both sides during a continued series of voluntary movements, and that his even occurred when the movement was being thought of but not executed. The microstructure and connectivities of the SMAS are considered in relationship to its proposed key role in being excited by the mental act of intention and then calling up the appropriate motor programs to give the desired movement: each mental intention would act on the SMA in a specific manner; the SMA has an 'inventory' and the 'addresses' of stored subroutines of all learnt motor programs and so is able to institute the desired movement by its neuronal connectivites. In conclusion there is a general account of the concept of the liaison brain both for intention and perception.