Evoked potentials of the central visual system during and after hypoxia in cats

1. 1. In chronically prepared cats, evoked potentials of the visual cortex (VC) to flash stimulation of the eye or electrical stimulation of the optic chiasm (OC) and optic radiation (OR), and those of the lateral geniculate body (LGB) to electrical stimulation of OC were recorded in parallel with spontaneous EEGs during and after hypoxia induced by inhalation of a hypoxic gas with oxygen tension of 18–20 mm Hg. 2. 2. After the onset of hypoxia, all electrical activity was transiently activated. Then it declined and finally disappeared. VC was affected earlier than LGB, and the postsynaptic activity disappeared earlier than the presynaptic activity, in LGB as well as in VC. 3. 3. The recovery of some evoked activities proceeded smoothly for the first 20 min but thereafter slowed down, and sometimes deterioration again took place. 4. 4. EEG activity first noted in the recovery course consisted of fast waves of very low amplitude. 5. 5. EEGs and evoked potentials recovered almost completely when resuscitation procedures were applied before presynaptic activity of VC disappeared. 6. 6. In half of the cats electrographic seizures were observed in the recovery course. In one group seizure discharges occurred early in the recovery course and continued for a short time: in the other group seizure discharges occurred very late and laster much longer. In the latter group a complete recovery from the hypoxic effects was rarely obtained. 7. 7. There were some cases in which the electrographic activities completely recovered from the hypoxic effects but behavior remained abnormal.