Changes of P22 and P27 of Median Nerve Somatosensory Evoked Potentials Related to Recording Locations

J Korean Assoc EMG Electrodiagn Med 2003;5(1):33-38.
Published online May 10, 2003.

Abstract

Objectives:To investigate variability of P22 and P27 following N20 of somatosensory evoked potentials (SEPs) according to different recording derivations. Methods:Twenty-one healthy subjects underwent SEPs assessments of both median nerves. SEPs were recorded over 9 sites over both hemispheres. In middle array, one electrode was placed over C3’/C4’and two electrodes were placed 2 cm medial and lateral to C3’/C4’, respectively. In the anterior and posterior arrays 3 cm apart (anterior and posterior, respectively) from middle array, three electrodes were designated in same manner. Absolute latencies of the N20 and following positive peaks and amplitudes identified as N20-P22, N20-P27, or N20-P (one positive peak) were measured. Results:In the anterior array, P22 was more frequently evoked at position A of the dominant hemisphere and at all sites of non-dominant side, compared to P27. N20-P22 amplitude was smaller at position B comparing to position C on the non-dominant hemisphere, however, it was not changed on dominant side. In the posterior array, P27 was more frequent than P22 at all positions of the dominant hemisphere but it was similarly evoked on non-dominant side. Conclusion: P22 may be affected by P27, and therefore P27 is more dominant than P22 on the both hemispheres, suggesting asymmetry of neural generators distribution.

Key Words: Somatosensory evoked potential, P22, P27