Imitation and matching of hand and finger postures.

Converging evidence from patients with unilateral brain lesions, from a patient with callosal disconnection, and from functional imaging in healthy subjects suggests different competencies of both hemispheres for imitation and matching of hand and finger postures. Whereas the left hemisphere is fully competent for processing hand postures, an additional right hemisphere contribution is needed for finger postures. I propose that the left hemisphere is responsible for coding gestures with reference to knowledge about the structure of the human body, whereas a right hemisphere contribution is needed for visuospatial exploration and analysis of gestures. Single case studies of patients with visuoimitative apraxia and results of functional imaging suggest a prominent role for left area 40 for body-part coding. Additional activation of left MT/V5 in the functional neuroimaging study may be related to processing of the motion implied by the gesture which is presented as a static image.