Lateralization for Facial Emotional Behavior: A Methodological Perspective

Abstract

Recent attention has focused upon the neuropsychological mechanisms underlying facial emotional expression. The greater intensity of expression and more extensive muscular involvement of the left hemiface have suggested right hemisphere dominance in the expression of emotion. This interpretation is based on the fact that the lower portion of the face is predominantly innervated by the contralateral cerebral hemisphere. The current paper reviews a series of studies on (a) facial asymmetry in normal subjects, (b) facial emotional expression in brain-damaged subjects with unilateral lesions, and (c) peripheral factors mediating facial expression findings. Neuropsychological mechanisms underlying emotional processing are also discussed. Our finding of left-sided facial asymmetries in normals is underscored by our finding that right brain-damaged patients are impaired in the expression of facial emotion. Finally, our studies have demonstrated that the asymmetries in normals and the deficits in patient populations are not artifacts of hemiface size and mobility or facial paralysis and apraxia. Taken together, these studies provide evidence that the right hemisphere is specialized for the expression of facial emotion.