DISSOCIATION BETWEEN UPPER AND LOWER NECK N-13 POTENTIALS FOLLOWING PAIRED MEDIAN NERVE STIMULI

Cervical N13 potential in response to the median nerve stimulation can be recorded either from upper (Cv2) or lower (Cv6) neck with almost e qual amplitudes and latencies. It has long been debated whether they r epresent the same or different generator sources. Using a conditioning -test paired stimuli paradigm, we examined the differences of recovery function of Cv2- and Cv6-N13, anterior neck (AN)-P13, and scalp recor ded P13/P14 in 6 healthy subjects. All cervical electrodes were refere nced to the non-cephalic site. Scalp response was recorded with linked ear reference. The inter-stimulus intervals ranged from 4 to 20 ms wi th 2 ms increments. Throughout 3 to 18 ms ISI, Cv6-N13, AN-P13 and sca lp P13/P14 were suppressed, whereas Cv2-N13 was facilitated. All but s calp P13/P14 returned close to the control at 20 ms ISI. The findings indicate that Cv2-N13, Cv6-N13 and scalp P13/P14 are independent each other and arise from different generator sources. The suppression of C v6-N13 is consistent with a postsynaptic nature of this potential and may indeed be mediated through dorsal horn intemeurons creating a curr ent held orientation in the posterior-anterior direction. The facilita tion of Cv2-N13 suggests that this is a presynaptic potential and may travel through the dorsal column with vertical orientation. The longer period of suppression of scalp P13/P14 suggests it to be of polysynap tic origin and to arise at least rostral to the cuneate nucleus. (C) 1 997 Elsevier Science Ireland Ltd.