If you have ever been curious about the structure of sleep, you may want to learn about a concept called sleep architecture. This idea helps us to understand the pattern of the stages of sleep, how this changes as we get older, and what impact sleep disorders may have.
Defining Sleep Architecture
Sleep architecture represents the cyclical pattern of sleep as it shifts between the different sleep stages, including non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. It allows us to produce a picture of what sleep looks like over the course of a night, taking into account various depths of sleep as well as arousals to wakefulness. Sleep architecture can be represented by a graph called a hypnogram.
There are generally four to five sleep cycles during a night and each lasts from 90 to 120 minutes. Early in the night, you may transition from lighter sleep stages (called N1 sleep) to deeper, slow-wave sleep (called N2 and N3 sleep). REM sleep may appear, and it becomes more common during the latter part of the night, alternating with N2 sleep.
How Sleep Architecture Changes with Age
As we get older, both the amount and the quality of our sleep may change. Slow-wave sleep decreases and lighter N1 sleep increases. As a result, it becomes easier to awaken and more time may be spent awake, leading to insomnia.
The Impact of Sleep Disorders on Sleep Architecture
There are certain sleep architecture abnormalities that may exist in the context of sleep disorders. If REM sleep occurs earlier than 90 to 120 minutes into sleep, this may suggest various causes, including:
- Irregular sleep-wake rhythm
- Withdrawal from tricyclic antidepressants or MAO inhibitors
Other sleep disorders such as sleep apnea may lead to disruptions of the natural sleep architecture with frequent arousals leading to numerous sleep stage shifts and abnormal cycling of sleep.
American Academy of Sleep Medicine. "International classification of sleep disorders: Diagnostic and coding manual." 2nd ed. 2005.
Hirshkowitz, M. et al. "Polysomnography of adults and elderly: sleep architecture, respiration, and leg movement." J Clin Neurophysiol. 1992 Jan;9(1):56-62.