Comparison of cervical SEPs on median, radial and ulnar nerve stimulation.

Cervical responses (SEPs) to stimulation of the median, radial and ulnar nerves were studied in 9 healthy subjects. In recordings from e Cv7 electrode referenced to a scalp electrode P11 presented a bilobed (P11a + P11b) profile for all three nerves whereas from Cv2 only P11b appeared as a rule. P11a and P11b were more distinct in the ulnar than in the median and radial nerves. The P11 onset-P13 onset interval was virtually the same for the radial and median nerves and approximately 0.4 msec longer for the ulnar nerve. This difference probably represents the Cv8 to Cv6 intramedullary conduction time. An exact evaluation of P11 onset is possible only in low cervical recordings, though the P11 peak may be a useful landmark when recording from Cv2. P11a would appear to originate at (or near) spinal entry, P11b high in the cervical cord and P13 at supraspinal level.