Psychological testing at high altitudes.

Psychological testing was done on 20 subjects at various altitudes (sea level, 3,8,10 m, and 5,000 m) during a 35-d mountaineering expedition to Denali (Mt. McKinley). Intellectual functioning and personality changes were studied. While little variation was noted at the lower altitude, at 5,000 m there was a marked deterioration in cognitive ability. This was accompanied by a sharp increase in paranoia and obsessive-compulsiveness and smaller increases in depression and hostility.