CAFFEINE REDUCES LOW-FREQUENCY DELTA-ACTIVITY IN THE HUMAN SLEEP EEG

In view of the hypothesis that adenosine is involved in sleep regulati on, the effects of the adenosine antagonist caffeine on sleep and slee p EEG were investigated in eight young males. Compared to the placebo condition, caffeine (100 mg) administered at bedtime prolonged sleep l atency and reduced sleep efficiency and stage 4 of non-rapid eye movem ent sleep (NREMS). Electroencephalographic slow-wave activity (SWA, sp ectral power density in the 0.75-4.5-Hz band) was reduced, whereas pow er density in the spindle frequency range was slightly enhanced. The s uppression of SWA was limited to the first NREMS episode. Caffeine red uced the power density mainly in the lowest delta band, in contrast to the changes during physiological sleep that encompass both the delta and theta bands. Caffeine levels in saliva, assessed in a separate exp eriment, decreased from 7.5 mu mol/l in the first hour of sleep to 3.5 mu mol/l in the seventh hour. In the night following caffeine adminis tration, stage 4 sleep had reverted to the baseline level, but sleep l atency was still increased, and stage 2 sleep, as well as SWA in the f irst NREMS episode, were reduced. The data show that even a low dose o f caffeine affects the sleep EEG. However, the effects of caffeine did not completely mimic the spectral changes observed during physiologic al sleep.