鏡焦点における緩電位変動並びにニューロン活動の検討

STEADY POTENTIAL SHIFTS AND NEURONAL ACTIVITIES IN THE MIRROR FOCUS DURING EXPERIMENTAL FOCAL SEIZURES

I．はじめに

　ヒトおよび動物において，一側大脳半球にてんかん焦点（原焦点）が形成されると，その反対側対称部にも，脳波上発作波の出現が認められ，GastautとFisher—Williams^2）により"鏡焦点"として報告されているが，この鏡焦点の機能，ことに①鏡焦点部においても，原焦点と同様に，ニューロンの同期した高頻度発射が認められるのか，②原焦点とは独立した自動性を保持する鏡焦点が存在するのか，の主な2点について，Morrell^7〜9）をはじめとする肯定的な報告と，Ajmone-Marsan^1）らにより代表される否定説があり，まだ意見の一致が見られていない。

　我々は，ネコの一側大脳皮質にペニシリンを塗布することにより発作波を惹起し，鏡焦点部において，発作波に伴う緩電位変動およびニューロン活動の分析を行ない，先に報告^5）した原焦点部での成績と対比して検討を加えた。

Epileptogenic foci were made on the pericruciatecortex in cats by penicillin application. Steadypotential (SP) shifts associated with ECoG parox-ysms and activities of the cortical units at the siteof the original focus were then compared with thosein the contralateral homologous region (mirrorfocus).

1) Soon after the isolated paroxysms were notedat the original focus, the projected discharges wererecognized at the mirror focus. The projected dis-charges showed a maximum amplitude in the ex-actly homologous region and there observed triflingnegative SP shifts only in the superficial corticallayers.

2) In the mirror focus, a substantially smallernumber of units were activated, whose greaterparts were detected at the superficial cortical layers,and their firing patterns seldom consisted of syn-chronous high frequency bursts of spikes.

3) Commonly, when the paroxysms of spike-after-discharges appeared in the original focus, only spikedischarges were projected to the mirror focus.

4) In rare occasions, there existed the paroxysmsof spike-after-discharges or typical tonic-clonic sus-tained paroxysms in the mirror focus, where theSP shifts and the neuronal activities were similarto those in the original focus.

5) These results suggested that the isolated ECoGparoxysms observed in the mirror focus representedkinds of the superficial electrical phenomena acti-vated transcallosally, since neuronal aggregatelocated in the deep cortical layers were scarcelyactivated in these situations.