Evidence supports the idea of distinct stages in sleep

• A landmark study by William Dement and Nathaniel Kleitman (1957) monitored the sleep patterns of nine adult participants in a sleep lab
• brainwave activity was recorded on an EEG and the researchers controlled for the effect of caffeine and alcohol
• REM activity during sleep was highly correlated with the experience of dreaming, brain activity varied according to how vivid dreams were, and participants woken during dreaming reported very accurate recall of their dreams
• Replications of this investigation have noted similar findings though the small size of the original sample has been criticised by some
• nevertheless this study suggests that REM sleep is an important component of the ultradian sleep cycle cycle