SENSORY FACTORS IN PURPOSIVE MOVEMENT

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Abstract
A study was conducted in monkeys to delineate the role of limb afferents in purposive movement. It was determined that the ability to use a limb purposively is in direct relation not only to the extent of intact efferent connections from the total central nervous motor mechanisms to the muscles of the limb, but also to the extent of intact afferent connections to those neural mechanisms. Full use of grasping requires the integrity of at least one dorsal root distributing cutaneous sensation to the hand, and the presence of a fragment of the grasp reflex and instinctive grasp reaction. In the absence of this, a less perfect form of grasping can occur in monkeys by elaboration of the proximal traction response, a righting reflex obtained from stretch of the shoulder adductors. Simple flexion and extension and associated movements of the limb can occur if the total mechanism of the tonic neck reflex remains intact. The degree of motor ability obtainable following complete or partial deafferentation of a limb is therefore in direct relation to the most complex residual of neck, proximal traction, and contactual responses.