Changes of Scalp-Recorded Somatosensory Evoked Potentials Related to Recording Methods

J Korean Assoc EMG Electrodiagn Med 1999;1(2):207-211.
Published online May 9, 1999.

Abstract

Objectives : To establish the distribution of near-field potential (NFP) and far-field potential (FFP) of somatosensory evoked potentials (SEPs) recorded at the scalp with different recording methods. Methods : SEPs elicited by stimulation of the right median nerve were recorded in 30 healthy subjects. Thin steel needle electrodes were placed subcutaneously with 5 different recording montages; C3´-Fz; C3´-left upper extremity (LUE); C4´-Fz; C4´-LUE; Fz-LUE. We compared the SEPs recorded with each recording montage by measuring N1 and P1 potentials occurring over 15 msec after stimulus. Results : N1 and P1 latencies of the responses at C3´ and C4´ were not significantly different each other and not changed with recording method. However, N1-P1 amplitude was considerably affected by recording montage. With comparison of potentials recorded at Fz and C3´, N1 latency of SEPs at C3´ was not different from P1 latency at Fz. Conclusion : Subcortical FFPs and cortical NFPs would be distributed in the region of C3´, however, only FFPs would be recorded at C4´. In addition, distant NFPs and FFPs are represented at Fz. With cephalic bipolar recording montage, N1 potential would be considered as a summation of N1 at C3´ and P1 at Fz.

Key Words: Somatosensory evoked potentials, Scalp, Near-field potential, Far-field potential