Chapter 9--face sensorimotor cortex neuroplasticity associated with intraoral alterations.

Loss of teeth or dental attrition is a common clinical occurrence associated with altered somatosensation and impaired oral motor behavior (e.g., mastication, deglutition, phonation). Oral rehabilitation aims at restoring these sensorimotor functions to improve patients' quality of life. Recent studies have implicated neuroplastic changes within the primary motor cortex (M1) in the control of limb motor behaviors following manipulations of sensory inputs to or motor outputs from the central nervous system as well as in learning and adaptation processes. However, limited data are available of the neuroplastic capabilities of face-M1 in relation to orofacial motor functions. The overall objective of our series of studies was to use intracortical microstimulation (ICMS) and recordings of evoked muscle electromyographic activity to test if neuroplastic changes occur in the ICMS-defined motor representations of the tongue-protrusive (genioglossus, GG) and jaw-opening (anterior digastric, AD) muscles within the rat face-M1 and adjacent face primary somatosensory cortex (face-S1) following several different types of intraoral manipulations. We found that a change in diet consistency was not associated with statistically significant changes in AD and GG motor representations. However, incisor extraction resulted, one week later, in a significantly increased AD representation within the contralateral face-M1 and face-S1, and incisor trimming produced time-dependent changes in the AD motor representation. These novel findings underscore the neuroplastic capabilities of the face sensorimotor cortex and point to its possible role in adaptation to an altered peripheral state or altered sensorimotor behavior. Further insights into the neuroplastic capabilities of the face sensorimotor cortex promise to improve therapeutic strategies aimed at the restoration of oral functions, particularly in patients suffering from orofacial sensorimotor deficits or pain.