Apraxia: Clinical Types, Theoretical Models, and Evaluation

Apraxia is traditionally defined as a disorder of skilled movement that cannot be attributed to elementary sensorimotor deficit, aphasia or severe mental deterioration (De Renzi, 1989). This negative definition has led to integrate within the same framework a multitude of relatively different clinical manifestations, which have little in common with the kind of deficits to which it was originally applied (e.g., gaze apraxia, gait apraxia, trunk apraxia). These forms probably concern automatic movements and, therefore, will not be treated here. It is now largely admitted that some clinical signs are particularly useful for the diagnosis. First, the disorder affects the two sides of the body, even though the brain lesions are generally unilateral and more particularly located in the left (dominant) hemisphere. Second, the errors made by apraxics vary depending on the conditions of testing. For instance, apraxics can succeed in many circumstances, but fail when the movement must be executed to the clinician’s request. In this frame, three categories of movement are regarded as relevant to the evaluation: Imitation of meaningless postures, pantomime production (i.e., demonstration of the use of a tool without the tool in hand) and actual tool use. Apraxia has been, and is still, subject to intense debate notably about its autonomy from elementary sensorimotor deficits and from higher-level cognitive processes. As a result, neurologists and neuropsychologists alike are commonly uncertain about the good way of assessing and interpreting it. In this chapter, we propose to address different issues relative to the notion of apraxia in light of recent developments made in the field.