脳波に及ぼす固視点と全体野の影響

INFLUENCE ON EEGS OF GAZING AT A FIXATION POINT AND OF GANZFELD

I．はじめに

　開・閉瞼による異常波誘発率は，閃光刺激によるそれと比較して低率ではあるにしても，開・閉瞼といういわば生理的刺激で誘発される異常波の持つ臨床的意味は大きい。また単に異常波賦活の有無だけでなく，開・閉瞼に伴う脳波変化から被検者の意識水準を推測し，それでわれわれは基礎波を記載する基準にもしている。

　ところで，従来ルーチンの検査として行なわれてきた開・閉瞼賦活はあまりにも単純な方法のためか，それに関与する諸要因の分析的的研究は少なく，成書^8）を見ても開・閉瞼賦活に関する記載は実に乏しい。

Influence on EEGs of gazing at a fixation pointand of Ganzfeld was studied in a total of 77 sub-jects; they were 5 normal adults, 66 epileptics and6 patients with various neuropsychiatric disorders.Of these 77 subjects, 16 showed normal awakeEEG and 61 abnormal awake EEG.

A white thick paper (18 cm by 26 cm) was placed20 cm before the eyes of a subject, and he wasmade to gaze at a black spot of 4 mm diametermarked at the center of this paper. This was con-tinued for 10 seconds. Then he was covered by awhite thin paper (30 cm by 34 cm) simultaneouslytaking off that paper marked a black spot, andhis eyes were kept open for 30 seconds (Ganzfeld).The brightness of both papers was kept at 40 cd/mm².He was not allowed to blink during theseexaminations.

The EEG changes by gazing at a fixation pointand by Ganzfeld were divided into the followingtwo: (1) desynchronization by the former andsynchronization by the latter, and (2) no significantchanges by both. The first group included alphaactivity (16 cases), posterior slow activity (12 cases),diffuse slow activity (3 cases), generalized par-oxysmal discharges (23 cases), and focal paroxysmaldischarges over the posterior cerebral regions (10cases). The second group included only focal par-oxysmal discharges over the anterior cerebral regions(13 cases).

It was suggested that the results obtained abovemight be explained by the following: ocular fixa-tion by gazing at a fixation point and visual stimu-lus of Ganzfeld act at the posterior cerebral regions,where the visual cortex is located; they also actat the centrencephalon either directly or indirectlyvia the visual cortex, but may not act at theanterior cerebral regions.