Electrical Activities of the Visual Cortex in Chronically Blinded Cats

Abstract

Elec-trical activities of the cerebral cortex, spontaneous and evoked, were studied in free behaving cats after both eyes were enucleated. Observations were continued for one month after eye enucleation. The evoked potentials were recorded from the visual and sensori-motor cortices (VC and SMC) before and after eye enucleation, keeping the stimulus parameters unchanged. The postsynaptic component (C4) of the VC evoked potential to stimulation of the lateral geniculate body or the optic radiation was potentiated after eye enucleation and this potentiation was maintained over 30 postoperative days with a gradual subsidence. The presynaptic component (C1) was also enhanced after eye enucleation, but this facilitation was far smaller than that of C4 component and was kept at the same level for a long period of postenucleation. The strength of potentiation of the VC evoked potential was different depending upon the vigilance level of experimental animals; the strongest potentiation was seen during light sleep and the weakest one during arousal. The post-excitatory recovery process of the deafferented VC was more or less delayed as compared with that of the intact VC. The visual de-afferentation did not induce any marked change in the SMC evoked potential. During arousal 10-16 c/s waves appeared as a dominant component of the eeg of the deafferented VC and during deep sleep bursts of 14-20 c/s spindle-like waves were seen with seemingly normal phasic waves (cortical deep sleep waves). A decrease in the wave components faster than 30 c/s was evident during arousal and deep sleep. In the sensorimotor cortical eeg those fast wave componr ents were increased.