THE TWO COMPONENTS OF THE GRASP REFLEX AFTER ABLATION OF FRONTAL CORTEX IN MONKEYS

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Abstract
Cutaneous and proprioceptive stimuli are the components of the grasp reflex electromyographically studied in 4 monkeys after removal of frontal cortex. The entire cortex in front of the precentral sulcus was removed in 2 of the animals and in the other 2 the precentral gyrus remained. The reflex was elicited by moving a stimulating object slowly across the palm. This produced no effect proximally but as it moved distally the fingers flexed, particularly at the interphalangeal joints, and when the stimulus reached the fingers a slight stretching and closing occurred. Locally anesthetizing the median and ulnar nerves in the palm and at the wrist with procaine showed that the cutaneous component is the essential trigger which conditions the finger flexors by activation of gamma motoneurones to muscle spindles and excitation of the motoneurone pool of the muscles for grasping when the stimulus stretches the muscles.