眼球運動による頭皮上の電位変化

POTENTIAL CHANGES OVER THE SCALP RESULTING FROM EYE MOVEMENTS

　眼球運動やまばたきがヒトの脳波曲線のartifactsの原因の1つとなることはよく知られていることであり，頭皮上直流電位測定の際，脳波曲線の基線が垂直あるいは水平眼球運動またはまばたきによつて動揺することの記載もある^1）。これらの動揺は網膜に対して角膜面が陽性になるような極性をもつ網膜に由来する電気的二重極の存在によるもので，眼球運動はこの電場を変化させるものである^2）。しかし，この波及に関する系統的な研究は数少なく^3），本研究では眼の周囲の皮膚上から測定される眼球運動電位（electro-oculogram，以下EOG）の大きさと頭皮上に伝播する電位の大きさとの定量的関係を求めた。

　この知識は最近多くの研究が発表されつつある期待に関する頭皮上の電位（contingent negative variation，以下CNV）とか随意運動に関する電位（motor potential，以下MP）や誘発電位の遅成分など頭皮上緩電位の測定に際して大いに役立つものと思われる。

An attempt was made to predict the amplitudes of potential changes on the head due to eye move-ments from those of the electro-oculograms (EOGs). Vertical and horizontal EOGs were led through the respective paired electrodes placed near the eyes and EEGs were monopolarly recorded in 5 normal subjects. The results obtained were as follows.

1) A downward eye movement induced a negative potential shift in v. EOG and also, though small, in EEG, while an upward movement resulted in a positive one.

2) In all 5 cases, potential amplitudes on the vertex during vertical eye movements showed a linear relation to those of v. EOG with statistical significance. The slope in that relation, i. e. pro-portional coefficient of vertex potential to v. EOG was found to be 0.19 to 0.25 in down rotation and O.14 to 0.22 in up rotation.

3) Topographical distribution of the eye move-ment potential along a central sagittal line did not correspond well to a simple exponential decay and the correlation between EEG and v. EOG became worse at the nearer to the occipital region. The slope at the forehead, Fpz was O.19 to 0.25 and O.14 to 0.22 in down and up movements, respec-tively.

4) Eyeblinks produced a monophasic positive po-tential in v. EOG and a positive change in EEG. The EEG changes over the head were not system-atic and predictable.