Morphology of somatosensory evoked fields: inter-hemispheric similarity as a parameter for physiological and pathological neural connectivity.

The morphology of somatosensory evoked fields (SEF) following electrical separate stimulation of left and right median nerve in 22 healthy volunteers was explored. The analysis of morphological properties of individual SEFs has been performed, in order to quantify an inter-hemispheric correlation coefficient. Despite a high inter-subject variability of the SEF morphologies, a high intra-subject inter-hemispheric shape correlation occurs in the post-stimulus epoch of 100 ms from the stimulus onset. Accordingly, a normative value for the parameter describing the SEF inter-hemispheric correlation coefficient has been calculated. The present work establishes quantitative and normative descriptions of the shape similarity of SEFs from the two hands in the left and right hemispheres. This provides a database for a new parameter, which might be useful in detecting alterations in the primary sensory cortical activation due to possible unilateral alterations of sensory inflow because of either peripheral or central deficits. The described procedure has been successfully applied to a small number of patients affected by unilateral cerebrovascular lesion.