ON THE REORGANIZATION OF SENSORY HAND AREAS AFTER MONO-HEMISPHERIC LESION - A FUNCTIONAL (MEG) ANATOMICAL (MRI) INTEGRATIVE STUDY

The topography of primary sensory cortical hand area following a monoh emispheric lesion (sudden = stroke; progressive = neoplasm) was invest igated in relationship with clinical recovery of sensorimotor deficits . Twenty seven patients with monohemispheric lesions were studied in a clinically stabilized condition. Functional informations from magneto encephalography (MEG) were integrated with anatomical data from magnet ic resonance imaging (MRI). MEG localizations of the neurons firing at early latencies in primary sensory cortex after separate stimulation of median nerve, thumb and little fingers of each hand were carried ou t. Characteristics of cerebral equivalent current dipoles (ECDs) activ ated by each contralateral stimulation, the 'hand extension' (i.e., th e distance in millimetres between ECDs of first and fifth digits), as well as interhemispheric differences of the tested parameters were inv estigated. Finally, ECDs' locations were integrated with MRI. Lesions involving cortical (C) or subcortical (SC) areas receiving sensory inp ut from the hand were often combined to increase interhemispheric asym metry of the tested parameters (22% for C and 49% for SC lesions). Thi s might be due to an activation of neuronal districts which in the aff ected hemisphere (AH) differ from those normally activated in the unaf fected hemisphere (UH) and in the control population. Moreover. the 'h and extension' was enlarged on the AH-more frequently after a SC lesio n-mainly due to a medial shift of the little finger ECD, combined to a tendency of both finger ECDs to shift frontally. After a C lesion, re sponses from the AH were often stronger than normal. Spatial reorganiz ations were also seen in the UH (7% of C and 14% of SC lesions). 'Hand extension' in the UH was selectively enlarged for the P30m only when combined with a similar enlargement in the AH. Significant interhemisp heric asymmetries due to neuronal reorganization in the AH were associ ated with worse clinical outcomes compared to patients without asymmet ries. (C) 1998 Elsevier Science B.V.