This scientific commentary refers to ‘Critical brain regions for tool-related and imitative actions: a componential analysis', by Buxbaum et al., (doi:10.1093/brain/awu111).
Apraxia is a symptom on the border between cognition and motor control. It is predominantly caused by left brain damage and frequently accompanied by aphasia. Theories of apraxia have been dominated by a model of the conversion of mental images into motor commands proposed more than 100 years ago by the German psychiatrist Hugo Liepmann and revived for modern cognitive neurology by Norman Geschwind and his colleagues in Boston (Fig. 1). There are several variants of this model but they agree that deliberate control of gestures involves the conversion of a concept of the intended gesture into motor commands, that this conversion is implemented in the brain as a posterior to anterior stream of neuronal processing, and that the parietal lobe occupies a crucial position in this stream (Goldenberg, 2009, 2013). However, in this issue of Brain, Buxbaum and colleagues present data from voxel-based lesion-symptom mapping experiments that suggest that revisions to the model may be required (Buxbaum et al., 2014).
Alternative versions of the posterior to anterior stream of motor control and of the central role of parietal lesions in apraxia. (A) Hugo Liepman (1920) proposed that mental visual images of intended actions were created in occipital regions and transferred to the precentral motor region for motor execution. Interruption of this stream leads to ‘ideo-kinetic’ (later renamed ‘ideomotor’) apraxia. Parietal lesions are likely to …