Neural correlates of differential finger gesture imitation deficits in left hemisphere stroke.

Behavioural studies in apraxic patients revealed dissociations between the processing of meaningful (MF) and meaningless (ML) gestures. Consequently, the existence of two differential neural mechanisms for the imitation of either gesture type has been postulated. While the indirect (semantic) route exclusively enables the imitation of MF gestures, the direct route can be used for the imitation of any gesture type, irrespective of meaning, and thus especially for ML gestures. Concerning neural correlates, it is debated which of the visuo-motor streams (i.e., the ventral steam, the ventro-dorsal stream, or the dorso-dorsal stream) supports the postulated indirect and direct imitation routes. To probe the hypotheses that regions of the dorso-dorsal stream are involved differentially in the imitation of ML gestures and that regions of the ventro-dorsal stream are involved differentially in the imitation of MF gestures, we analysed behavioural (imitation of MF and ML finger gestures) and lesion data of 293 patients with a left hemisphere (LH) stroke. Confirming previous work, the current sample of LH stroke patients imitated MF finger gestures better than ML finger gestures. The analysis using voxel-based lesion symptom mapping (VLSM) revealed that LH damage to dorso-dorsal stream areas was associated with an impaired imitation of ML finger gestures, whereas damage to ventro-dorsal regions was associated with a deficient imitation of MF finger gestures. Accordingly, the analyses of the imitation of visually uniform and thus highly comparable MF and ML finger gestures support the dual-route model for gesture imitation at the behavioural and lesion level in a substantial patient sample. Furthermore, the data show that the direct route for ML finger gesture imitation depends on the dorso-dorsal visuo-motor stream while the indirect route for MF finger gesture imitation is related to regions of the ventro-dorsal visuo-motor stream.

Reduced awareness for apraxic deficits in left hemisphere stroke.

OBJECTIVE: Reduced awareness for motor or cognitive impairments has mainly been studied in relation to right-hemispheric deficits such as left-sided hemiparesis. However, recent studies suggest that also left hemisphere (LH) stroke can lead to reduced awareness for neurological/neuropsychological deficits, for example, aphasia. The aim of the current study was to characterize reduced awareness for apraxic as well as aphasic deficits in patients suffering from LH stroke. METHOD: After the assessment of apraxia and aphasia, patients (n = 32) were asked to rate their performance on a 1- to 5-point rating scale. An unawareness score (UAS) was computed as the difference between the examiners' ratings and self-ratings, resulting in negative scores for patients who overestimated their performance in a given assessment, that is, exhibited reduced awareness for their stroke-related deficits. RESULTS: Patients with apraxia (n = 14) and aphasia (n = 16) significantly overestimated their performance in the respective assessment. However, the level of awareness was not generally related to the severity of apraxia, and there were no group differences in other variables between patients with full (n = 7) and reduced awareness (n = 7) for apraxic deficits. The reduction of awareness for apraxic deficits did not differ significantly for buccofacial versus limb gestures. CONCLUSION: Data show that LH stroke can lead to reduced awareness not only for aphasic deficits but also for buccofacial and limb apraxia. (PsycINFO Database Record