Nasopharyngeal recordings of N18 far-field potential            in Somatosensory Evoked Potential (SEP)

J Korean Neurol Assoc > Volume 17(1); 1999 > Article

Journal of the Korean Neurological Association 1999;17(1): 112-116.

체성감각 유발전위에서 N18 far-field 전위의 비강인두를 통한 접근

김대현, 차재관, 김상호, 김재우

동아대학교 의과대학 신경과학교실

Nasopharyngeal recordings of N18 far-field potential in Somatosensory Evoked Potential (SEP)

Dae-Hyun Kim, M.D.,Jae-Kwan Cha, M.D., Sang-Ho Kim, M.D., Jae-Woo Kim, M.D.

Dept. of Neurology, College of Medicine Dong-A University 1, 3-Ga Dongdaesin-dong, Seo-gu, Pusan 602-103, South Korea

Abstract

Backgrounds : The widespread N18 in the median nerve SEP is a broad negativity following positive far-field potentials and is widely distributed over the scalp. It is suggested that the N18 may be originated from subthalamus or upper brainstem nuclei. But there remains substantial controversy regarding its origin. Recently, it is proposed that the N18 is generated in the medulla. For the evaluation of its origin, we used nasopharyngeal electrode for recording SEP stimulated by median nerve stimulation.
Methods: Standard methods of recording SEP were used in 19 normal adults(36 sides, 19-68 years, 9 males). 11 patients with following locations of the lesions were studied: 2 high cervical cord, 1 ponto-medullary junction, 3 pons, and 5 thalamus. We evaluated the N18 potentials at ventral medulla level, using nasopharyngeal electrode and recorded them at scalp by non-cephalic reference recording. We compared the amplitude and duration of the N18 at scalp with those at nasopharyngeal electrode.
Results: The mean amplitude and duration of N18 at scalp showed no significant difference from that at nasopharyngeal electrode(1.76±0.4μV, 16.48±2.47 msec and 1.75±0.4μV, 16.56±2.19 msec, p>0.5). The N18 was absent in 2 patients with high cervical cord lesions. The amplitude and duration of the N18 were normal in all other patients with brainstem and thalamic lesions, including a patient with lesion at the ponto-medullary junction.
Conclusions: These results suggested that N18 is generated in the medulla and not more rostrally in the brainstem. Key words: Median nerve, Far-field potential, Somatosensory evoked potential