Short-latency somatosensory evoked potentials to median nerve stimulation: components N 13--P 13, N 14--P 14, P 15, P 16 and P 18 with different recording methods.

Comparative recordings of short-latency somatosensory evoked potentials with midfrontal (Fz), ear and non-cephalic reference electrodes were obtained in 12 normal subjects to define the site of the generators of the different components and the spatial distribution and interference of the different components recorded at the neck and scalp. Such investigations provide the basis for identical investigations in patients with focal lesions of the central nervous system. The N 13 recorded from the neck (C2-Fz) and the inconsistently recorded component N 14 were quite similar in latency to the far-field potentials P 13 and P 14 recorded at the scalp (C3', C4'--ear or hand). The component P 15 was clearly visible only in scalp-Fz leads and occurred 0.2--0.9 ms (mean 0.5 ms) later than P 14 in ear or hand reference recordings. This is evidence against the identity of these two components proposed by others. In a larger group of 48 subjects, using an exclusive Fz-reference lead, normal values were established of the components P 15, P 16 and P 18, as well as their scalp distribution.