Apraxia and inattention dissociate in chronic left hemisphere stroke
D.C. Timpert, P.H. Weiss-Blankenhorn, A. Dovern, S. Vossel, G.R. Fink (Jülich, Köln)
Theories of lateralized cognitive functions in the human brain propose (for right- handers) a dominance of the left hemisphere for motor control and language, and a dominance of the right hemisphere for attention. Accordingly, neglect is more frequently observed after right-hemispheric stroke, while apraxia and aphasia are a common sequela of left-hemispheric stroke. However, there are also – often neglected - clinical reports of attentional deficits after left hemisphere stroke. To elucidate the neural basis of such atypically lateralized attentional deficits, we here assessed - for the first time - the relationship of inattention and apraxia in chronic left-hemisphere stroke using behavioural and lesion analyses.
Attention and apraxic deficits were each characterized by five neuropsychological tests. Voxel-based lesion-symptom mapping (VLSM) was performed on the basis of clinical imaging.
Apraxic deficits were observed in 46.5% of the patients with chronic left-hemisphere stroke (n= 71). The prevalence of inattention (lateralized and non-lateralized inattention combined) was 18.3%. Interestingly, the severity of attentional and apraxic deficits did not correlate.
Apraxic imitation and object use deficits were significantly associated with left parietal and temporal lesions, respectively. The severity of attentional deficits was related to lesions in vicinity of the left intraparietal sulcus (IPS). Attentional deficits after chronic left-hemisphere stroke are hence more prevalent as commonly assumed, dissociate from apraxic deficits, and are associated with lesions of the left posterior parietal cortex. These findings challenge theories of strictly lateralized attentional functions in the human brain.