Vector short-latency somatosensory-evoked potentials after median nerve stimulation.

A new method has been developed for recording short-latency somatosensory-evoked potentials after median nerve stimulation. Negative electrical forces recorded with three orthodiagonal bipolar electrodes in the neck had a direction opposite to that of impulse conduction in the proximal peripheral and cervical somatosensory pathway. Sequential tracings of vectors opposite the electrical forces were made in three-dimensional display, thus reproducing the actual time sequence of electrical events in those structures. Fixed generators such as the subcortical nuclei were also analyzed with this technique, and multiple generators of N13 potential (N13a and N13b) were visualized. This technique may be useful in the functional evaluation of the somatosensory pathway in the cervical cord.