Magnetoencephalography in acute stroke

Stroke is probably the commonest causeof chronic and severe disability in the western countries and accounts for a large proportion of healthcare resources. For this reason the focus of research and health organisations is nowadays on the analysis of mechanisms for functional recovery and rehabilitation. We used MEG analysis of the neurons firing at early latencies in primary sensory cortex after separatestimulation of left and right median nerves (SEFs) in 25 patients with acute ischemic stroke and compared to normal controls. SEFs morphological characteristics and generators properties were evaluated as well as spontaneous activity spectral distributions; interhemispheric differences of the tested parameters were investigated and related to the clinical picture. Lesions of brain areas receiving sensory input from the hand were often combined to increase interhemispheric asymmetry of the testedparameters. Morphological excessive asymmetry selectively involving parietal regions was associatedto cortical lesions, whereas for primary sensory areas was affected by both sub- and cortical lesions. Enhancement of SEFs from the unaffected hemisphere was often encountered (25% of cases)and in two patients also from the affected hemisphere. A tendency of correlation between clinical picture and morphological SEF alteration appeared. The interhemispheric asymmetry of SEF and spontaneous activity analysis seems to represent a clinically relevant probe in tracking brain reorganisation following a monohemispheric lesion. Future studies are needed to validate MEG usefulness in following up medical, as well rehabilitative, procedures.