Presynaptic depolarization of corticofugal fibres participating in a feedback loop between trigeminal brain stem nuclei and sensorimotor cortex.

Abstract

PRESYNAPTIC depolarization of trigeminal afferent fibres evoked by stimulation of the cerebral cortex has been demonstrated in the trigeminal brain stem nuclei1 and presumably represents a pathway for modification of afferent input from the face and mouth. Anatomical studies2 have indicated that corticofugal fibres project directly to these nuclei, and ultrastructural evidence3 of axoaxonal synapses in the trigeminal main sensory nucleus (MSN) suggests that there are reciprocal synaptic relationships between trigeminal afferent and corticofugal fibres. In the light of this knowledge we carried out a study designed to demonstrate presynaptic depolarization of corticofugal fibres by trigeminal afferent fibre stimulation. While studying the orthodromic and antidromic responses of cortical cells in the face area of the sensorimotor cortex, we found a fast feedback pathway between trigeminal brain stem nuclei and the cerebral cortex.