Paradoxical cortical potential polarity of the upper extremity somatosensory evoked potential (SSEP) has been reported in cases of polymicrogyria (PMG) syndrome. To date, the pathophysiological basis of this electrophysiological aberration remains under investigation. Here we present a case of mild PMG that showed "layered" microgyri in the left frontoparietal cortices affecting both hand and foot sensorimotor areas. The SSEP recordings revealed an isolated polarity reversal of N20 from the dysplastic cortex. We postulate a central sulcus misfolding theory to explain the "positive" N20 potential recorded in the PMG cortex.
Keywords: Central sulcus; polymicrogyria; somatosensory evoked potential; transcranial electrical motor evoked potential.