MEMORY DEFICITS AT 0.6 MPA AMBIENT AIR-PRESSURE

We investigated the effects of an elevated ambient air pressure of 0.6 MPa on verbal memory performance. Twenty-four experienced divers were compressed in a dry hyperbaric chamber to pressures equivalent to 0.5 meters of seawater (msw) (n = 12) and 50 msw (n = 12). Verbal memory was assessed by free recall and recognition of visually presented word lists. The testing procedure specified learning and testing at surfac e, learning at surface and testing at depth, learning and testing at d epth, and learning at depth and testing at surface. Non-specific stres s was assessed by measurement of salivary cortisol, heart rate, and su bjective stress before, during, and after the dives. The 50-msw dive g roup showed a significant decrease of free recall performance when the material was learned at depth (P < 0.01). However, only postdive reca ll of material learned at depth remained significantly impaired (P < 0 .05), whereas recognition performance was normal. For both groups no s ignificant effects of depth on the investigated stress indices were ob tained. These results are taken as evidence that inert gas narcosis ma y interfere with encoding and/or retrieval of verbal information, alth ough the possibility that other stressors in the hyperbaric environmen t contributed to these deficits cannot be eliminated entirely.