Sleep architecture

Sleep architecture is the structure of a night's sleep, described by the sequence, duration and proportion of the stages the brain passes through.

A healthy adult night consists of four to six cycles, each lasting roughly ninety minutes. Each cycle moves from light non-REM sleep into deeper slow-wave sleep and then into REM sleep, with slow-wave sleep dominating the first half of the night and REM periods lengthening toward morning. The stages are identified in a sleep laboratory from brain-wave patterns, eye movements and muscle tone recorded by polysomnography, and the result is often drawn as a hypnogram, a stepped chart of stage against time.

Sleep architecture changes with age, with less slow-wave sleep and more brief awakenings in older adults, and it is disturbed by alcohol, many medications, sleep apnea, pain and shift work. Researchers report it through measures such as total sleep time, sleep efficiency, sleep onset latency, wake after sleep onset and the percentage of time spent in each stage. A night can feel long yet be poorly restorative if deep and REM sleep are fragmented. Cannabinoids have been studied for their effects on sleep stages, mainly in small trials, and the findings are early and inconsistent.