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The effects of hypobaric hypoxia on cognitive processing in humans were studied by recording event-related potentials (ERPs) from the scalp in a go/no-go reaction time (RT) paradigm under various simulated high altitudes. Most subjects indicated abrupt impairment of RT at high altitudes. RTs lengthened in association with changes in latency and amplitude of the N2-P3 components, reflecting sensory discrimination and evaluation processes. Some subjects did not suffer any changes in RT up to an extremely high altitude of 6,000 m. In the latter case, although the N2-P3 components did not undergo any changes, the P3 component was followed by a sequence of negative on-going (frontal maximum) and positive on-going (parietal maximum) slow waves. The amplitudes of these slow waves increased as altitude increased. Although these same waves appeared in the ERPs of subjects who demonstrated the increase in RTs at high altitudes, when the subjects failed in the RT task, both of the slow waves either disappeared or diminished. Such slow waves may be associated with attempts to maintain RTs against the deteriorative effects of hypobaric hypoxia.

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