Masticatory force and function in patients with hemispheric brain infarction and hemiplegia

Recent functional animal studies have reported that the motor control of ma sticatory muscle function is bilaterally guided by both hemispheres, which may fundamentally differ from the cortical control of limb muscle function. In this study, we investigated. whether unilateral cortical brain infarcti on induces different impairments in masticatory and upper limb motor perfor mance. Evidence of the importance of both hemispheres iu controlling mastic atory movements would be greater if the masticatory function were shown to be unimpaired in patients with severe hemiplegia. The masticatory function of 16 patients with severe hemiparesis caused by brain infarction in the re gion of the middle cerebral artery was studied by means of interview, clini cal examination, and bite-force measurements. Finger-thumb grip-force measu rements and clinical examination of the upper limbs were also performed for evaluation of the effect of infarction on upper limb motor function. Local ization of the infarction was confirmed with computer tomography and magnet ic resonance imaging. The Scandinavian Stroke Scale demonstrated that each patient had a major unilateral cortical infarction which had caused a marke d handicap with a serious impairment of upper limb function on the contrala teral side. The clinical examination revealed no major signs of temporomand ibular disorders, and the masticatory muscles, when examined by palpation, contracted symmetrically. None of the patients with unilateral brain infarc tion showed any differences in bite farces between the healthy and paralyze d sides. These results indicate that, in hemiparetic patients, great differ ences may exist between the motor performances of the masticatory and upper limb muscles. The present investigation clinically illustrates the importa nce of both hemispheres in the control of masticatory function and movement s.