ABSTRACT

The motor area of the cerebral cortex (MCx) is known to be involved in the control of limb movements, particularly, of the distal musculature, providing hand and finger movements. This function is realized via the pyramidal system, which has not only polysynaptic but also (in primates) monosynaptic connections with distal muscle motoneurones (Baker et al., 1995; Kuypers, 1964; Phillips and Porter, 1977). Accordingly, the motor cortex is known to control precision and fineness of motor actions, particularly isolated finger movements and their coordination, such as during the precision grip. Following motor cortex lesions in primates, separate finger movements disappear and are replaced by a synergistic flexion of all fingers (Bucy et al., 1966; Tower, 1940; Wiesendanger et al., 1994). Compensation for the behavioural deficit after pyramidal tract impairment was shown to be provided by the red nucleus, controlled by the motor cortex and cerebellum, and by the rubrospinal system (Lawrence and Kuypers, 1968; Ioffe, 1973, 1975; Ioffe and Samoylov, 1967) which, along with the pyramidal system, belongs to the lateral descending system (Kuypers, 1964).