VISUAL-IMITATIVE DISSOCIATION APRAXIA

Liepmann posited that, in right handers, the left parietal lobe contai ns movement formulas or representations. Therefore, performance failur es may be induced by degraded representations, a failure of these repr esentations to influence motor systems or a failure of stimuli to full y access these representations. Imitation may help the performance of subjects with degraded representations. However, patients who have imp aired visual access to movement representations may perform more poorl y with imitation than to verbal command. Trajectories of repetitive 's licing' gestures made by a previously reported subject (Raymer et al.) with an infarction in the left visual association cortex (left occipi tal and inferior temporal lobe) that spared the parietal lobe were con trasted with those of three apraxic subjects with lesions that include d the left parietal lobe and four non-brain-damaged control subjects. AII subjects were asked to produce the gesture to verbal command and t o imitation. Movements of the left hand, wrist, elbow and shoulder wer e digitized from neighboring views, reconstructed in three dimensions, and analysed graphically and numerically. The apraxic subjects with l eft parietal damage were unable to maintain the proper linearity and s patiotemporal attributes of their wrist motions and showed interjoint coordination deficits. Their deficits were most pronounced to verbal c ommand, with their movements improving though remaining poorly perform ed when they imitated. The subject with the left occipital and inferio r temporal lesion that spared parietal cortex, however, showed an oppo site pattern. This subject exhibited close to normal performance when producing the movement to verbal command, but significant deficits whe n imitating. (C) 1997 Published by Elsevier Science Ltd.