Neuroplasticity of face primary motor cortex control of orofacial movements.
We have carried out a series of studies to address the role of the face primary motor area (MI) in the cerebral cortex in trained or semi-automatic orofacial motor behaviours and in behavioural adaptations to an altered oral environment. These studies have utilized intracortical microstimulation (ICMS), reversible cold block or single neurone recordings in face MI. Our studies in monkeys have revealed that face MI plays a strategic role in elemental and learned motor behaviours and in certain aspects of chewing and swallowing. Furthermore, successful training of awake monkeys in a novel tongue-protrusion task is associated with significant neuroplastic changes in face MI. These findings in monkeys are supported by correlated findings in humans which have revealed significantly enhanced corticomotoneuronal excitability when humans learn the novel tongue-protrusion task. Our related ICMS studies in rats reveal that trimming or extraction of the rat's lower incisors or damage to the rat's lingual nerve can result in significant changes in the MI representations of the tongue or jaw muscles. These various findings suggest that the face MI is important in orofacial motor skill acquisition and adaptation to an altered occlusion or loss of teeth or lingual sensory function, and that it reflects dynamic and modifiable constructs that are modelled by behaviourally significant experiences and that are critical to learning and adaptive processes.