Subcortex and Apraxia

The following are taken from articles in Brain and Cognition 40:1999 special issue.

Merians AS et al. Patient with aphasia due to corticobasal degeneration did better pantomiming to command than using an actual tool. This contrasts to apraxic patients with left parietal damage who pantomime worse but do better with actual tool. Authors speculate that apraxia in CBD is due to SMA/convesity/premotor areas not parietal (or putamen). They differentiated convexity premotor and SMA premotor cortices. SMA lesions cause apraxia but it implements internally generated programs (projecting from parietal). The CBD patient did not have that much trouble with internally generated programs.

Jacobs et al. studied the same CBD patient as Merians et al., plus two others and evaluated neuropsychologically extensively. They noted adequate gesture comprehension, poor production, a tendency to gesture better with eyes open than closed, normal tests of memory and other basic neuropsychological tests, impaired learned and novel gesture production, impaired gesture imitation. Cortical sensory loss may be important. The network responsible may include the CN/PUT, SMA, convexity and inferior parietal lobule.