ネコの大脳感覚領および視床における脳波活動性について

On the EEG activities of cerebral sensory area and thalamus in cats

I．はじめに

　脳波を示標にして脳の興奮性をおしはかる場合多くの問題点がある。たとえば覚醒反応パタンで，Berger^7）はα波の減少を抑制過程と考え，Adrian^1）は逆に非同期化興奮説をとなえた。現在では後者が支持されているがその生理学的意義はかならずしも明らかでない。

　最近SatoとMimura^36），Satoら^41）やMimura^23）らは感覚刺激中の脳波の周波数スペクトルの微細構造を調べ，刺激前の安静時のα波の消失や減弱の他にそれよりも速いかまたはのろいα波の発現をみいだした。しかも従来，刺激によつて現われると信じられていたβ波は逆に安静時α波と同様に減弱することも明らかにした。佐藤^{31）〜33）}，Satoら^39）はさらに脳波の自己相関図（平均的時間経過）およびスペクトル密度はそれぞれ適当な単一衝撃刺激に対する脳波導出部の脳（脳波系）の平均反応の時間パタンおよび周波数パタンを示し，しかも「興奮性」を一般化した平均「活動性」の時間的および周波数パタンを示すことも明らかにした。その上適当な感覚刺激によつて得られる脳波活動の周波数応答（周波数特性）は脳波導出部位の脳の「活動性」の周波数パタンを示し安静時脳波のスペクトル密度と同等であることも示した。

1) The EEG" activities" (frequency respon-ses) in the cerebral sensory areas (bilateral lateral and posterior sigmoid gyri) and thala-mic nuclei (left centre médian and rigt late-ral geniculate body) of cats, unanesthetized and immobilized with Flaxedil, were investi-gated by delivering 3~11/sec photic flicker stimulation to the right eye alone and sync-hronously combined stimulation of this flick-er and electric shock to the right main pad.

2) It was observed in the frequency spect-ra obtained from the autocorrelograms of the ECoGs before and during the photic flicker stimulation and the combined stimulation that not only the augmentation of the cerebral activities of the stimulating frequency and its high harmonic frequency but also the inh-ibition of the inherent activities were simult-aneously verified by the stimulation.

3)" Activity" driven by the photic flicker stimulation alone in the cerebral sensory area (lateral gyrus, posterior sigmoid gyrus) was augmented by the combined stimulations of about 3~7/sec, whereas it was inhibited by the stimulations of about 7~11/sec. Though the" activity" in the thalamus (centre médian and lateral geniculate body) was inhibited by the combined stimulation of the latter frequ-ency, no obvious effects were observed in the instances of former stimulations.

4) It would be able to conclude, therefore, that the inhibitory process induced by cutan-eous stimulation in the visual cortex will be followed by the same process as in the thala-mic level, while the augmentative one will be caused predominantly by the convergence of retinal and cutaneous afferent impulses in the cortical neurons themselves.

5) The" activity" of the lateral geniculate body was influenced by the stimulation to the cutaneous receptors to suggest the cutaneous effects upon the visual" activities".