Impact of left versus right hemisphere subcortical stroke on the neural processing of action observation and imagery

Purpose: Mental training appears to be an attractive tool in stroke rehabilitation. The objective of this study was to investigate whether any differences in the processing of action observation and imagery might exist between patients with left and right hemisphere subcortical strokes. Methods: Eighteen patients with strictly subcortical stroke (nine right-hemispheric) underwent a functional magnetic resonance imaging (fMRI) study with an experimental paradigm in which motor acts had to be observed and/or imagined from a first person perspective. Changes in hemodynamic activity were measured using fMRI. Results: The activity level was found to be higher in the non-lesioned compared to the lesioned hemisphere. Patients with lesions in the left hemisphere had a higher activation level in visual (fusiform and lingual gyri), superior temporal areas and dorsal premotor regions across all performed comparisons than those with right hemisphere lesions. Furthermore they had more vivid imagery experiences and lower scores on the Stroke Impact Scale. Conclusions: Patients with left hemisphere subcortical lesions recruit more cortical regions in the processing of action pictures and videos. This recruitment was further enhanced during imagery. This is most likely related to the fact that the lesion touched the dominant hemisphere.