Sleep Stage

From N1 to REM: Brain Wave Patterns and Subjective Experience at Each Stage

In stage N1, alpha waves (8 to 13 Hz) begin to give way to theta waves (4 to 7 Hz). The stage is short, one to five minutes, and any outside stimulus wakes you easily. Subjectively you often feel you are still awake, and sensations of falling or loose, disconnected images (hypnagogic imagery) may appear. In stage N2, sleep spindles and K-complexes emerge, and this stage takes up roughly half of the night. Responses to outside stimuli fade, and fragmentary thoughts and brief dreams are reported. In stage N3, delta waves (0.5 to 4 Hz) occupy 20 percent or more of the epoch, and this is the deepest sleep. Waking is difficult, and being roused from it brings strong sleep inertia, the groggy state. In REM sleep, the EEG shows a pattern close to waking while the skeletal muscles of the body go slack. Long dreams that unfold as stories are most often experienced in this stage, and because the muscles are released, you can run in a dream while your body stays still under the covers.

REM Is Not the Only Stage in Which We Dream

The claim that we dream only in REM sleep circulated for a long time, but experiments questioned it early on. In the 1960s, studies woke participants from specific sleep stages (Foulkes, 1962) and showed that dream reports could be obtained from NREM sleep as well. Being woken from NREM sleep, N2 in particular, and describing some kind of mental activity is not at all unusual. NREM dreams and REM dreams do differ in quality, however. REM dreams are longer, more vivid, unfold as narratives, carry stronger emotion and include strange elements. NREM dreams are shorter and more fragmentary, draw on everyday material and feel closer to thinking than to a story. Most of the striking dreams that dream interpretation works with come from REM sleep, yet the brief visions at sleep onset (N1) and the vague unease of deep sleep (N3) are also part of dream experience. There is no need, then, to dismiss a dream as not a real one simply because it did not arrive at dawn.

How Sleep Stages Are Scored: The Limits of Consumer Devices

Scoring sleep stages accurately requires polysomnography (PSG). Three biological signals are recorded at once, the EEG, the electro-oculogram (EOG) and the electromyogram (EMG), divided into 30-second epochs and scored by a technologist. Commercial smartwatches and sleep trackers, by contrast, only estimate sleep stages from body movement and heart rate. The accuracy of that estimate varies widely between devices and studies, and telling N1 from N2, or REM from wakefulness, is reported to be especially difficult. So even when a device announces that you had little deep sleep, that display does not necessarily reflect your actual sleep stages. The numbers are genuinely useful as a record of when you went to bed and how long you slept. Treating the stage breakdown as a rough guide for comparing one night with another, rather than a verdict, keeps you from being pushed around by the figures and makes it easier to keep a dream journal going.

Putting Sleep Stages to Work on Dream Recall

Knowledge of sleep stages can also be put to practical use in remembering more dreams. A common approach is to get up one to two hours earlier than usual, stay properly awake for 20 to 30 minutes, and then go back to sleep. REM sleep is already longer in the later cycles of the night, so if you bring your mind fully awake during those hours and then return to bed, your chances of waking during or at the end of REM sleep rise, and you carry the dream back with you while it is still vivid. It is realistic to try this on a day off, when the following day has room in it.

The other idea is to arrange your sleep in multiples of 90 minutes, aiming to wake at the end of a sleep cycle. Cycle length is only said to be around 90 minutes, though; it varies from person to person and even within a single night. Since it cannot be cut cleanly by the clock, it is sensible to use it as a guide when deciding a bedtime, no more. With either method, cutting into your sleep to do it exacts a larger price in daytime sleepiness than it returns. Choosing a day when you want to remember a dream and trying it now and then is about the right distance to keep.