ABSTRACT
Apraxia designates the impaired ability to perform a gesture, in spite of preserved motor, somatosensory, and coordination functions in the limb engaged in the action. A unitary account of apraxia and aphasia runs into the same difficulty that undermines the theory of a common source for praxis skills and handedness, namely the occurrence of dissociations in either direction. The low frequency with which left hand apraxia is found in patients with left premotor cortex damage, is difficult to reconcile with the assumption that the parietal output must necessarily reach this area before making connections with the right premotor cortex and suggests that the left parietal lobe can use alternative pathways. Caution should be exercised when attempting to assess the bearing on apraxia of monkey lesion experiments, because the motor tests used in them are based on operant conditioning and call for the repetition of the same sequence in response to a given stimulus.
