A study of sensory projection from jaw muscles to the cerebral cortex in the rat

The sensory projection from jaw muscles to the cerebral cortex have been studied in rats by electrophysiological and histochemical methods. Electrical stimulation of individual masticatory muscles elicited bilateral responses in the cortical areas 8, 10, 2, and 2a. The following pathway was postulated to mediate these cortical responses; impulses of muscle origin are conducted in turn to the trigeminal mesencephalic tract nucleus (TMT), the contralateral thalamic nucleus ventralis posteromedialis (VPM), the cerebral cortex and finally to the other cerebral cortex which is ipsilateral to the side of stimulation. The ipsilateral cortical response appeared about 5 msec later than the contralateral one and was abolished by sectioning the corpus callosum. By stimulating the cerebral cortex antidromically, the conduction time to the VPM was found to be as long as 6 msec. The conduction from the TMT to the contralateral VPM consumed a period of more than 10 msec. It was presumed to be multisynaptic, being based on the finding that horseradish peroxidase injected into the VPM could not be recovered in the contralateral TMT.