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 somatosensory evoked potentials (SEPs) in 21 healthy subjects by simultaneous recordings with noncephalic or ear reference from multiple scalp sites. The cortical onset was defined as the fork at which the contralateral parietal and frontal or ipsilateral parietal waves diverged. We found the N20 onset 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 N20 onset latency is more stable than N20 peak.