New subcortical components of the cerebral somatosensory evoked potential in man.

Two new components of the human SEP upon stimulation of the contralateral median nerve at the wrist have been identified. Such components have been called N16 and N17, according to their polarity and latency. N16 and N17, as well as the N14-P15 complex, are generated by separate subcortical dipoles. Particularly, they are supposed to be far-field reflections of the activity of the dorsal columns nuclei or the medial lemniscus (N14-P15), the thalamus (N16) and the thalamo-cortical radiation (N17). Moreover, it has been established that N14 is the very first intracranial component of the human SEP, the main peak of S wave and the preceding ones being extracranial in origin. A new classification of SEP intracranial components including early (N14 through N17), intermediate (N20 through P30) and late events is proposed.