Brain and Nerve No to Shinkei Volume 38, Issue 5 (May 1986)

REPRODUCIBILITY OF THE SOMATOSENSORY EVOKED POTENTIALS IN NORMAL HUMANS Shingo Kawamura 1 , Akifumi Suzuki 1 , Kimio Yoshioka 1 , Hiromi Nishimura 1 , Masako Nara 2 , Nobuyuki Yasui 1 1Department of Surgical Neurology Research Institute for Brain and Blood Vessels-AKITA 2Department of Division of EEG, Research Institute for Brain and Blood Vessels-AKITA pp.475-480
Published Date 1986/5/1
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The authors have applied the somatosensory evoked potentials (SEP) as an index of the brain function, and studied the reversibillity of the ischemic brain dysfunction from the SEP changes under the drug-induced conditions. From the pre-vious experiences, the authors are now doing the quantitative analysis of the amplitude of the early negative component (N1-amplitude) on SEP, and evaluating the reversibility of the brain dys-function. The early components of SEP, including N1 were reported that responses were reasonably constant in normal subjects. Responses recorded at different times in the same subject were usually very similar and there were not significant dif-ferences among the responses recorded in different subjects. In the consecutive SEP recordings, how-ever, the reproducibility of N1-amplitude has not yet fully studied. It is necessary to know the standard values when the significant changes of N1-amplitude are evaluated under the drug-induced conditions.

The purpose of this paper is to study the repro-ducibility of N1-amplitude of SEP in the consecu-tive recordings, and also, stimulating and record-ing methods of SEP. Subjects were 15 normal volunteers, from 21 to 38 (mean : 29) years old. Two stimulating needle electrodes were inserted to the skin at the wrist, and the somatosensory stimulation was applied to the median nerve with 1 msec duration of square pulse. Monopolar EEGs were recorded from the scalp of the parietal re-gion (P3 or P4) contralateral to the stimulation, and SEPs were recorded by averaging those EEGs with computer technique. N1-amplitude was deter-mined by the vertical distance between peaks of P1 and N1 components.

The results were as follows : 1) The reproducibility of N1-amplitude in the consecutive recordings was dependent on the fre-quency of averaging summation. But, it is difficult to record constant EEG for a long period because of motion artifacts or sleep. And the authors considered the limit 5 minutes. So, if stimulation pulses were generated every one second regularly, the limit of the frequency was considered 250-300 times.

2) The stimulus intensity did not have an influ-ence on the reproducibility of N1-amplitude, if the stimulus intensity was adjusted nearly above the thumb twitch threshold.

3) Components of SEP could not be recognized 500 msec after the somatosensory stimulation. Therefore, the stimulus interval of 1 sec was reasonable. With the regular stimulation, however, rhythmic EEG waves could not be averaged out.

4) In the consecutive SEP recordings by ave-raging 250 times every one second with the stimulus intensity of the thumb twitch threshold, N1-amplitude ratio, which compared Ni-amplitude of the first record with that of the second or third record, revealed between 0.440 and 1.62 (p <O.05).

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Brain and Nerve 脳と神経
38巻5号 (1986年5月)
電子版ISSN 2185-405X 印刷版ISSN 0006-8969 医学書院