The palmo-mental reflex. An electrophysiological study.
Repeated electric stimulation of the ulnar nerve fibers was applied at the wrist in 7 normal and 32 pathological subjects; the response reflexes were simultaneously recorded in the chin muscles and at the upper limb, on the flexor carpi ulnaris. Although it is possible to obtain two distinct polysynaptic reflexes by cutaneous stimulation of the limb, the palmo-mental reflex causes a unique response, the latency of which may diminish to 35 msec. This response occurs most often at the threshold which elicits a nociceptive reflex of the upper limb. The palmo-mental reflex is almost always bilateral for a unilateral stimulation and in numerous instances is characterized by a wide receptive field. These findings suggest that the palmo-mental reflex is an early event in a general nociceptive response. In the normal subject this fragment of a general response to a painful stimulus is highly suppressed as are the local reflexes by suprasegmental control. The palmo-mental reflex is liberated and augmented in the event of habitually bilateral lesions of the pyramidal tract or the extra-pyramidal formations.