Chapter 37 Hemiparesis

Abstract

Publisher Summary The primary sensorimotor and adjacent brain areas following a vascular insult undergo remarkable neuroplastic changes, mainly within the affected hemisphere (AH), but also in the unaffected hemisphere (UH). When the damage affects the core of the sensorimotor areas, reorganization is crucial for functional recovery; meanwhile, reorganization outside the usual boundaries never reaches the same functional efficiency of the original circuits. Interhemispheric asymmetries were more frequently encountered in the “subcortical” than in the “cortical” type of lesions. It is noteworthy that larger than normal amplitudes of somatosensory evoked responses with an asymmetrical waveshape were found frequently from the AH, especially following a cortical lesion. A somewhat similar pattern of abnormality is seen in patients showing larger than normal motor evoked potentials (MEPs) during transcranial magnetic stimulation (TMS) of the UH; this is usually combined with absent response from the AH and was a bad prognostic index. The functional reorganization of the motor output following a hemispheric stroke has been repeatedly reported, often with an excessive asymmetry of the sensorimotor hand topography between the AH and the UH. “Map migration” is usually on the medio-lateral axis, but an anteroposterior shift of up to several mms of the map's center of gravity has also been observed.