Frequency analysis of EEG in rats during the preconvulsive period of O2 poisoning.

The EEG of rats exposed to hyperbaric oxygenation (HBO) displays electrical discharges prior to the onset of generalized clinical convulsions (GCC). The characteristics of preconvulsive electrocorticogram (ECoG) in awake, unrestrained rats exposed to 3, 4, and 5 ATA O2 were determined. The ECoG was continuously monitored and analyzed by a hybrid analog-digital system until GCC developed. The time integral of rectified voltage of the individual delta (0.5-4 c/s), theta (4-8 c/s), alpha (8-13 c/s) beta 1 (13-20 c/s), and beta 2 (20-30 c/s) bands were plotted vs. time. An elevation in delta and a temporary reduction in alpha activity before the onset of the first electrical discharge (FED) was observed. There was a continuous reduction in beta 1 and beta 2 frequency bands during the entire pre-electrical discharge period. The activity of theta, and alpha frequency bands was significantly elevated only about 1 min before the onset of the FED, and of beta 1 and beta 2 during appearance of the FED. The possible relationship between the occurrence of preconvulsive EEG changes and pathological effects of hyperbaric oxygenation is discussed.