Visual evoked cortical potentials in men during compression and saturation in He-O2 equivalent to 400, 800, 1200 and 1600 feet of sea water.

Visual evoked cortical potentials and related EEG activity were recorded from subjects during rapid compression and exposure to pressures of 400, 800, 1200 and 1600 fsw. In one phase, subjects made repeated excursions to 1200 fsw from a base at 800 fsw; in the second phase, the saturated base was 1200 fsw with excursions to 1600 fsw. The results included: (1) For the visual evoked potentials, sizeable and significant decreases in amplitude and increases in latency of the response with depth; (2) Changes in the visual evoked potentials which varied systematically with depth but not with related changes in compression rate or decompression. The changes were small but consistent alterations of normal responses to visual stimulation; and (3) Theta activity in discrete EEG recordings increased progressively with depth. With all subjects showed increases in theta activity the pattern of increase varied individually.