Characteristics of EEG activity during high altitude hypoxia and lowland reoxygenation.

The aim of the present study was to determine the effect of high altitude (HA) immigration on cerebral electrical activity. Electro-EncephaloGraphic (EEG) activity were recorded from 25 lowland soldiers during eyes-closed resting conditions under the following conditions: 7 days at lowland before ascending to altitude (Test 1), during the first 7 days (Test 2) and 30 days (Test 3) at 3800m altitude, and 7 days after return to lowland (Test 4). The EEG was Fourier transformed to provide absolute and relative power estimates for the alpha, beta, delta, and theta bands. HA immigrants showed changes of EEG power confined in the posterior parietal cortex, right posterior temporal cortex, and occipital cortex. Compared with baseline Test 1, acute acclimatization (Test 2) only decreased theta power; chronic acclimatization (Test 3) discriminately increased alpha and beta powers but decreased delta power; after descending to lowland (Test 4), alpha power decreased, beta power remained increase, but delta and theta power recovered to the baseline level. Our findings demonstrated different EEG patterns during hypoxia exposure at HA as time goes on and after following reoxygenation at lowland, showing hypoxia decreased lower EEG frequencies while hypoxia/reoxygenation increased higher EEG frequencies. Our findings supports for the hypothesis that certain behavioral and physiological changes induced by sojourn at altitude could be caused by alterations in central nervous system function.