Orofacial motor control impairment in Parkinson's disease

Motor impairments in lip, jaw, and tongue muscles in patients with idiopathic Parkinson's disease (PD) were quantified. These orofacial muscle groups are nonuniformly endowed with muscle afferents, thus permitting evaluation of the hypothesis that certain PD motor symptoms are due to aberrations in muscle afferent function. Tongue muscles, devoid of stretch reflexes, were most impaired, while jaw-closing muscles, with numerous spindles and a monosynaptic stretch reflex, manifested the least impairment. Seemingly, PD motor impairments are independent of fusimotor or muscle afferent dysfunctions.