EEG and visual evoked potentials of conscious man during moderate hypothermia

Five conscious, normal humans were cooled by water immersion until their core temperatures were near 33.5 degrees C. When hypothermic at this level, small shifts of EEG frequencies to more theta and beta and less alpha activity occurred in comparison to normothermia. There was no significant change in the amplitude of the EEG. Although 10-20% increases in the latency of peaks in the visual evoked potential occurred in some subjects when hypothermic, this was not statistically significant, nor was the slight amplitude reduction. The results confirm for conscious, unanesthetized humans that moderate hypothermia to the level of 33.5 degrees C is on the borderline for significant alteration of brain electrical activity by cold, a general conclusion that was known previously only for anesthetized or immobilized humans and other mammals.