Apraxias

Abstract

Apraxia is defined as the difficulty or inability to perform learned skilled actions. Identifying apraxia in patients has prognostic implications. The praxis network is predominantly in the left hemisphere, and comprises parietal lobe regions that connect to several circuits involving the frontal, temporal and occipital cortices and the basal ganglia. This review discusses the types of apraxia and the disorders associated with apraxia, highlighting studies based on corticobasal syndrome and stroke as disease models. The evolution of historical concepts of praxis leading up to the current ‘pathway’ models is discussed in the context of neuroanatomical and imaging studies. Bedside testing and interpretation of apraxia are elucidated with examples. Key Concepts Apraxia is the difficulty in performing acquired actions and can be seen independent of other symbol‐mediated disorders such as aphasia. Apraxia is associated with several neurodegenerative disorders such as corticobasal syndrome, as well as with strokes and head trauma. There are several different forms of apraxia such as ideomotor, ideational and orofacial apraxia, and each is characterised by the specific manner in which action performance or interpretation is compromised. The praxis network involves circuits from frontal, temporal and parietal cortices and the basal ganglia. Left parietal lobe is pivotal for the praxis network. Newer models of praxis propose bilaterally represented ventral and dorsal processing streams, with the dorsal stream further subdivided into dorso‐dorsal and ventrodorsal substreams. The dorso‐dorsal or the ‘grasp’ system processes characteristics of a tool such as size, shape and orientation, while the ventrodorsal or the ‘use’ system stores object‐specific actions. In patients with left hemisphere damage, apraxia often coexists with aphasia; in patients with right hemisphere lesions, apraxia is often associated with a visuospatial disorder. Testing of apraxia at bedside is important for diagnostic and prognostic reasons.