COGNITIVE PERFORMANCE DURING A SIMULATED CLIMB OF MOUNT-EVEREST - IMPLICATIONS FOR BRAIN-FUNCTION AND CENTRAL ADAPTIVE PROCESSES UNDER CHRONIC HYPOXIC STRESS

:High altitude is characterized by hypoxic environmental conditions an d is well known to induce both physiological and psychological disturb ances. In the present study, called ''Everest-Comex 97'', the authors investigated the effects of high altitude on the psychosensorimotor an d reasoning processes of eight climbers participating in;a simulated c limb from sea level to 8,848 m over a 31-day period of confinement in a decompression chamber. Tests of visual reaction time, psychomotor ab ility, and number ordination were used. The climbers' data were compar ed with data from a similar laboratory study at sea level in control s ubjects. Continued testing of the control subjects at sea level clearl y led to learning effects and improvement of performance in psychomoto r ability and number ordination. In the climbers, similar learning eff ects occurred up to an altitude of 5,500-6,500 m. With further increas es in altitude, the climbers' psychomotor performance and mental effic iency deteriorated progressively, leading to significant differences i n psychomotor ability and mental efficiency between control subjects a nd climbers (9 and 13% respectively at 8,000 m and 17.5 and 16.5% resp ectively at 8,848 m). Three days (72 h) after the climbers had returne d to sea level, their mental and psychomotor performances were still s ignificantly lower than, those of control subjects (by approximately 1 0%). In contrast, visual reaction time showed no significant changes i n either climbers or control subjects. It is suggested that chronic hy poxic stress could alter selectively mental learning processes, i.e. e xplicit, rather than implicit (stimulus-response learning processes) m emory and cortico-limbic rather than basal ganglia-sensorimotor system function.