Imagining the impossible: intact motor representations in hemiplegics.

Motor imagery is known to involve brain regions vital to the performance of motor skills including primary motor cortex. The present results show that, following cerebral vascular accidents (CVAs) affecting a variety of these regions, many adults with left or right upper-limb paralysis (i.e. hemiparesis/hemiplegia) retain the ability to accurately represent prehensile movements involving the impaired limb. This suggests that during the acute phase of recovery many CVA patients can use motor imagery to activate partially damaged motor networks; a process that may facilitate functional reorganization. This ability was, however, compromised in cases with right posterior parietal or left frontal lesions. This pattern is consistent with the hypothesis that imagined prehension, like actual reaching and grasping, involves a network of highly interconnected areas distributed throughout parietal and frontal cortices.