Stability of N20 onset or peak latency in median somatosensory evoked potentials

We analyzed onset and peak latencies of the N20 response of median nerve so matosensory evoked potentials (SEPs) in 21 healthy subjects by simultaneous recordings with noncephalic or ear reference from multiple scalp sites. Th e cortical onset was defined as the fork at which the contralateral parieta l and frontal or ipsilateral parietal waves diverged. We found the N20 onse t unchanged between noncephalic and ear reference recordings, or among the recordings around the contralateral centroparietal scalp. The N20 peak was prolonged when the recording position moved posteriorly. We suggest that N2 0 onset latency is more stable than N20 peak. (C) 2000 John Wiley & Sons, I nc.