Planar vector projection of short-latency median nerve somatosensory evoked potentials

A planar vector projection of short-latency somatosensory evoked potentials (SEP) following stimulation of the median nerve was obtained by recording SEP over Fpz-Oz and T3-T4 and plotting the amplitudes on both channels at corresponding time points against each other. The resulting curve showed three successive loops pointing ipsilateral occipital (N1), contralateral occipital (N2) and ipsilateral frontal (N3) to the stimulated side. Normal values for latency, amplitude and direction of these loops were obtained from 10 normal adults. N1 can be attributed to the cuneate nucleus and medial lemniscus, N2 to the primary somatosensory cortex and N3 to the frontal cortex.