It is at this uneasy crossroads between coffee and sleep that researchers are now focusing their attention. By recording brain electrical signals in forty volunteers, they found that the brain maintains heightened activity, incompatible with fully restorative sleep. When Coffee and Sleep Clash in Young AdultsThe effects of caffeine on sleep are not uniform. In their case, brain signals measured during the night were more disrupted, particularly during REM sleep. According to data from the researchers, caffeine also changes the way electrical signals fluctuate throughout the night.