Properties of neurons in primate face motor cortex in relation to orofacial movements and influence of face primary somatosensory cortex

grantor: University of TorontoThere is little information of the sensorimotor cortical mechanisms controlling semiautomatic orofacial movements and the role of sensory inputs to the motor cortex (MI) during orofacial movements. An electrophysiological investigation was conducted in the unanaesthetised monkey to study (a) the activity patterns of single neurones recorded in face MI during orofacial movements, (b) the effects of reversible cold block of ipsilateral face primary somatosensory cortex (SI) on the orofacial movements and related activity of face MI neurones, and (c) modulation of somatosensory responses of face MI neurones evoked by orofacial stimuli during chewing. Face MI neurones exhibited a variety of neuronal activity patterns during chewing as well as a trained tongue-protrusion task. Most of the chewing-related neurones showed activity associated with rhythmic jaw movements or food preparatory movements. Some of the neurones showing the task- and/or chewing-related activity also showed significant alterations in activity in relation to swallowing. Unilateral cold block of SI had little effect on the performance of the orofacial movements or on task and chewing and/or swallowing-related activity of most face MI neurones. These data suggest that movement-induced reafferentation via the ipsilateral face SI may not be a significant factor in accounting for the activity of most face MI neurones related to orofacial, movements. A diminution of orofacial-evoked neuronal responses was a general feature of face MI during chewing. This suppression appeared dependent in part on an intact ipsilateral face SI in only a small portion of neurones tested during cold block of SI. These data support the view that the gain of somatosensory afferent inputs to MI can be adjusted to compensate for the increased sensory input produced during or as a result of movements but ipsilateral face SI may play a minor role in this mechanism. These findings indicate that face MI may play an important role in the control of not only voluntary but also semi-automatic orofacial movements and that ipsilateral face SI may have only a limited role in influencing MI neuronal activity.Ph.D