大脳皮質電気活動の同期化現象の検討—ことに視床腹外側核の影響について

THE INFLUENCE OF THE VENTROLATERAL THALAMIC NUCLEUS UPON CORTICAL SYNCHRONIZED ACTIVITIES

I．緒言

　Morison, Dempsey^1）2）以来thalamo-cortical relationに関連して膨大な研究が進められてきた^3）。このうち，大脳皮質電気活動の同期化現象については，recruiting　response （漸増反応・RR），紡錘波様後発射（triggered　spindle, spindle tripping or evoked spindle）および自発紡錘波の波形の類似性から，その発生のメカニズムの類似性が古くより推測されている^2）4）。さらにaugment—ing response （増強反応・AR）とRRについても，両者の画一的区別は行い難く，いずれともいい難い中間的な所見の報告も散見される^5）〜7）。また，Spiegel, Wyc—is^8）により創始され広く行なわれるにいたった定位脳手術の術中検索によってえられたヒトの成績についても，同様の報告が見受けられる^9）10）。

　そこで，われわれは視床腹外側核を中心として，AR・紡錘波様後発射および自発紡錘波について，その生理学的性質をネコとヒトの対比のもとに実験的に検討し，大脳皮質電気活動の同期化のメカニズムを明らかにせんとした。

Augmenting response (AR), spindle-like after discharges and spontaneous spindle waves were analized to investigate physiological role of the ventrolateral thalamic nucleus upon cortical syn-chronized activities in man as well as in cat.

In man, three positive and three negative waves, namely I-P, I-N, II-P, II-N, III-P and III-N, were obseved as essential cortical evoked responses after single threshold stimulation of the ventrolateral thalamic nucleus.

The condition of the parameters of stimulation to evoke AR in man was investigated, and the results were as follows.

It was necessary to evoke AR that the stimula-tion was strong enough to evoke big II-N, III-N and clear positive and negative waves after III-N, namely IV-P, IV-N, and that the stimulation should be done between decending phase of III-N and ascending phase of IV-N of the response evoked by preceeding stimulations. More precisely, typical pattern of AR was evoked when stimulations were done between peaks of III-N and IV-P. Recruiting-like AR was evoked when stimulations were done between peaks of IV-P and IV-N.

Then, in order to study the mechanism of cortical synchronization, VL-evoked cortical responses were investigated in cat immobilized under local anes-thasia. Recording electrode was located on the ipsilateral anterior sigmoid gyrus.

As the intensity of the thalamic VL stimulationwas increased, afterdischarges of the negative wave, which appeared with long latency (about 200msec.) increased in number and developed into spindle-like pattern with notches on the afterdischarges.

The long latencied negative wave in cat and IV-N in man were considered to correspond to Lehtinen's "precursor of the evoked spindle ac-tivity". Therefore, close relationship was indi-cated between AR and spindle-like afterdischarges. Futhermore, the similarities of the pattern between spindle-like afterdischarges and spontaneous spindle waves in cat, and attenuation of ipsilateral spon-taneous spindle trains after destruction of the ventrolateral thalamic nucleus in cat as well as in man were also observed.

From these facts, it seemed for us that these cortical synchronized activities, namely AR, spindle-like afterdischarges and spontaneous spindle waves were considered to be brought by similar physi-ological mechanisms with some varieties of synchro-nization ascribed to arousal levels under influences of activities of the ventrolateral thalamic nucleus.

And from laboratory experiment concerning evoked spindle-like pattern with notches, mecha-nism of waxing and waning phenomenon of spindle waves may be explained to be representation of beats of two rhythmic activities having slight discrepancy in frequency on the thalamo-cortical projection.