海馬と眼運動系の機能的協関

海馬反覆電気刺激による視運動眼振の変動

抄録

To investigate functional correlation between the hippocampus and the oculomotor system we attempted a series of experiments in which rabbit hippocampus was successively given a certain amount of electric stimulation for 10 days and resulting changes in the activity of the oculomotor system were measured using the test for optokinetic nystagmus, the test for spontaneous nystagmus and the electroencephalograms (EEG, s).
The results obtained were as follows :
(1) In rabbits with a single electric stimulation of the hippocampus, optokinetic nystagmus was first inhibited after the electric stimulation and then restored to the state before the stimulation (Type 1 : from inhibitory to normal).
In rabbits with repeated electric stimulation of the hippocampus, optokinetic nystagmus was first inhibited after the electric stimulation and then developed into the following 3 types : i.e., Type II (continuous inhibition), Type III (from inhibitory to excitatory) and Type IV (from inhibitory to excitatory combined with inversion of nystagmus).
(2) There was a close correlation between activity of optokinetic nystagmus and that of the EEG's. That is, the inhibitory phase of optokinetic nystagmus paralled the suppressive phase of the EEG's, whereas the excitatory phase of optokinetic nystagmus paralled that of the EEG's. Furthermore, the excitatory phase of optokinetic nystagmus tended to be acompanied by the appearance of nystagmuc responses due to electric stimulation of the hippocampus.
From these findings we conclude :
(1) The hippocampus initially exerts an inhibitory action on the activity of the oculomotor system.
(2) Continuous, abnormal excitation of the hippocampus can induce alterations in the reactivity of the oculomotor system. Such alteration is characterized by the appearance of the the two phases of the reaction : i.e., the first inhibitory and the second excitatory, with regard to development of optokinetic nystagmus.