Defective pantomime of object use in left brain damage: apraxia or asymbolia?

Disturbance of pantomime of object use in patients with left brain damage (LBD) and aphasia has been firmly established but its nature remains controversial. It may be due to an inability to perform movements from memory without external support by objects (apraxia) or to an inability to produce signs referring to absent objects and actions (asymbolia). The need to perform movements without external support is shared with imitation of gestures, and the demand to designate absent objects with drawing from memory. Both of these tasks have been found to be impaired in LBD. We examined pantomime of object use, drawing objects from memory, imitation of meaningless gestures, and aphasia in 40 patients with LBD and aphasia and compared them to healthy controls and to patients with right brain damage (RBD). Whereas drawing showed comparable sensitivity to LBD and RBD, pantomime was distinctly more disturbed in LBD than in RBD patients. Pantomime was worse than drawing in LBD but better than drawing in RBD. In the LBD group scores on pantomime showed significant correlations of very similar strength to drawing, imitation, and all language tests. Multidimensional scaling of the correlational structure placed pantomime in an intermediate position between verbal and non-verbal tests. We conclude that neither apraxia nor asymbolia can satisfactorily explain our results. It seems as if pantomime of object use taps a central aspect of left hemisphere function which is compromised by any LBD. We propose that this may be the ability to select and combine distinctive features of objects and actions.