Neuroplastic changes in motor representations within the primary motor cortex (M1) have been described after peripheral manipulations and implicated in motor learning and adaptation processes. It is unclear whether dental manipulations, which may result in altered oral sensorimotor functions, are associated with analogous changes within face-M1. This project applied intracortical microstimulation (ICMS) and recordings of evoked muscle electromyographic (EMG) activity to test if changes occur in the ICMS-defined motor representations of tongue-protrusion (genioglossus, GG) and jaw-opening (anterior-digastric, AD) muscles within face-M1 and adjacent face primary
somatosensory cortex (face-S1) following trimming or extraction of the rat’s right
mandibular incisor, or a change in diet consistency.
ICMS mapping was carried out in anaesthetised adult male rats. Consistent with previous findings, AD and GG had extensive motor representations showing
considerable overlap in naïve and sham control rats. AD and GG motor representations
were also found within face-S1. Left and right AD (LAD, RAD) had significantly larger
representations with shorter onset latency of ICMS-evoked EMG responses within
contralateral face-M1.
A change in diet consistency for 2-3 weeks was not associated with significant
changes in AD and GG motor representations within face-M1. Compared to control rats,
iii incisor trimming out of occlusion for a period of 1 week resulted, 1 day later, in a
significantly longer GG onset latency in ipsilateral than in contralateral face-M1; 1 week later, despite a regain of normal occlusion, GG and GG/AD overlapping representations were significantly larger and the centre of gravity (at AP 4.0) was significantly deeper in contralateral than in ipsilateral face-M1. Incisor extraction was associated, 1 week later, with significantly larger RAD and RAD/GG overlapping representations and a lateral
shift of LAD and RAD centre of gravity. Extraction also induced significant changes in AD and GG motor representations within the contralateral face-S1.
These novel findings indicate that face-M1 can undergo neuroplastic changes in
association with intraoral manipulations and also suggest similar neuroplastic
capabilities for face-S1 motor outputs. These findings contribute to our understanding of the role of face-M1 and face-S1 in sensorimotor adaptations to an altered oral state and provide the basis for several future studies.Ph
