Interhemispheric differences of sensory hand areas after monohemispheric stroke: MEG/MRI integrative study

Seventeen clinically stabilized monohemispheric stroke patients were studie d in order to investigate the chronic topographical modifications induced o n primary sensory cortical hand areas by a monohemispheric stroke within th e middle cerebral artery territory. Magnetoencephalographic (MEG) localizat ion of the cortical areas activated following electrical separate stimulati on of the median nerve, thumb, and little fingers was integrated with magne tic resonance imaging. Spatial localization of Equivalent Current Dipoles ( ECDs) of the short-latency cortical responses generated in primary sensory cortices, "hand area" (distance between 1st and 5th digits ECDs), interhemi spheric differences of such parameters, as well as of somatosensory-evoked fields waveshapes were investigated and compared with a control population. Lesions involving the cortico-subcortical areas receiving sensory input fr om the hand induced excessive asymmetry of MEG spatial parameters and respo nse morphology between the unaffected (UH) and the affected hemisphere (AH) . "Hand area" was significantly larger on AH in 20% of cases after a subcor tical, and in 13% after a cortical, lesion. Responses from AH were excessiv ely delayed in 20% ECDs. Interhemispheric ECDs strength differences were la rger than normal in 25% of cases after both types of lesions; the strength in the AH being enlarged after all cortical, and only 24% of subcortical st rokes. In a significant percentage of monohemispheric strokes, excessive in terhemispheric differences were found between AH and UH, suggesting that br ain areas outside the normal boundaries and usually not reached by a dense sensory input from the opposite hand and fingers may act as somatosensory " hand" centers. Correlation analysis between clinical outcome and cortical r eorganization in the AH suggests that this mechanism is linked with hand se nsorimotor recovery. (C) 2001 Academic Press.