Cortical Projections of the Nucleus Ventralis Posteromedialis (VPM) Neurons Receiving Somatosensory Input from Intraoral Structures in the Cat Thalamus

Abstract

In order to examine the functional significance of intraoral somatosensory input to the cerebral cortex, I studied the cortical projections of tongue and periodontal neurons in the VPM of the cat.
Experiments were carried out on cats anesthetized with urethane and chloralose. Single unit activities were recorded from the thalamus using glass capillary microelectrodes filled with 2% pontamine sky blue in 0.5M sodium acetate. The lingual nerve was stimulated electrically and the chorda tympani was cut to exclude gustatory input.
Cortical potentials evoked by electrical stimulation to the lingual nerve were recorded from SI, SII and SIII of the somatosensory areas, and a part of the gyrus coronalis. Neurons activated by the innocuous mechanical stimulation of intraoral structures were located in the lateral subdivision of the nucleus ventralis posteromedialis parvocellularis (VPMpcl) and the medial part of the VPM proper. Neurons in the VPMpcl responded primarily to the tongue, ipsilateral to the recording site, whereas those in the VPM proper responded to contralateral intraoral structures.
Neurons in the VPMpcl, as well as those in the VPM proper of the SI, were antidromically excited by electrical stimulation of the gyrus coronalis. Repetitive electrical stimulation of the gyrus coronalis induced jaw opening movements resembling mastication.
These experiments indicated that there are projections from the VPMpcl and the VPM proper to the cerebral cortex, and suggested that somatosensory inputs from intraoral structures play an important role in masticatory control.