Ideomotor apraxia: a call to action.

Although ideomotor apraxia (IM) has been a topic of investigation since the early 20th century, progress in studying the disorder has been hindered by important (and sometimes unarticulated) differences in the underlying theoretical models of various investigative groups. As a result, it is difficult to draw conclusions about the expected performance of IM patients on various tests of praxis (e.g. pantomime, single object use, gesture imitation, and naturalistic action); the relationship of IM to ideational apraxia (IA); the degree to which specific error types are diagnostic of one or the other disorder; the relationship of semantic knowledge to gesture representations; and the role of spatiomotor systems external to the stored gesture representation system. Here an updated model of IM is presented, informed by recent physiological and functional neuroimaging literature, as a step towards resolving some of these concerns. The model is intended to lay the groundwork for future investigations of specific performance patterns in different subtypes of IM.