If you tend to be a target for ads about everyday-carry tools, as I am, it’s understandable that you would want to sleep better, because sleep—despite its uncertain origin and adaptiveness—is the original EDC tool. It appears to benefit creativity, emotional regulation, threat evaluation, memory processing and other covert cognitive processing, waste disposal, and maybe even beauty, just as Grandma told us, though she probably didn’t know about the extracellular matrix.
I don’t mean to suggest that these are independent functions. It wouldn’t surprise me if some of the functions of sleep were necessary to accomplish others.
But are you getting the right amount of sleep? Some variations are inherited and others are acquired, though of course that’s not an either-or dichotomy. Even short-sleepers will be affected by deprivation of sleep beyond their limits of normal function, for example.
If you’re getting too little sleep—or too much, for that matter—and you have no medical problem, a sleep app could help. There are a lot of them on the market. Some are designed to help you sleep and others are meant to track your sleep. While you can quickly tell whether a sleep-aid recording of ocean waves puts you to sleep, it’s harder to know whether a sleep tracker is doing its job. Some reviews are pretty harsh, but they’re intended to keep you from wasting time and money.
So here’s a basic problem: How do we measure sleep? If all a sleep tracker does is to tell you how much time you spent in bed, you might as well stick with your clock.
There are two popular ways of measuring sleep, actigraphy and polysomnography. Your wrist tracker uses actigraphy to monitor your movements, and the results are relatively easy to interpret. Their usefulness was recently confirmed but found to be limited. It’s interesting that the actigraphy results were validated against a polysomnography standard.
Polysomnography is a more complicated system of measuring body signals that extend way beyond movement to include autonomic activity and the electroencephalogram, or EEG. Examining its results really opens up a window on sleep.
In a teaching lab, it’s easy to apply a few electrodes to a student’s scalp, amplify the recordings, and display the difference between beta and alpha rhythms in the EEG. That’s not polysomnography, but it’s a start that we can duplicate offline.
The EEG is a record of voltage changes between a couple of scalp electrodes. The microvolt variations can be amplified and stored in a computer or printed out on a polygraph or “EEG machine”. There are standard maps for applying electrodes, and you can get the gist of it here.
You probably recall hearing that there are four stages of slow-wave sleep (SWS) plus a stage with rapid eye movements, or REM. It’s more convenient and just as informative to deal with three stages of SWS by collapsing stages 3 and 4, so that is what sleep clinicians started using a few years ago. Identifying the stages and scoring a person’s status is still no picnic. Your general strategy in describing sleep is mapped out there.
BIO: Of course biology underlies a lot about sleep that an app doesn’t measure, but what about the biology that makes a sleep app useful?
Sleep onset is regulated in part by about one percent of the ganglion cells in the retina that contain melanopsin and send their output to the suprachiasmatic nucleus (or SCN: short version, long version), which regulates sleep timing and duration in partnership with a homeostatic drive mechanism, commonly labeled process C and process S. The timing and duration of sleep reflect genetic variation as well as photic entrainment.
Is it just that simple? Dual-process models are perennially attractive in explaining behavior, but connecting each process to the details of brain function often proves daunting. You can see how understanding is advancing, though, if you can muster the gumption required by this artlcle, which is particularly useful for explaining process S.
PSYCHO: Of course psychology organizes a lot about sleep that an app won’t measure, but what about the psychology of what an app does measure?
The stages of sleep can be scored with some precision using the EEG, but they are evident in a rough way to anyone who observes a sleeper, even a sleeping pet. People and pets are easily awakened from a stage 1 doze. Breathing slows in stage 2 and a snorer will often begin to snore in stage 3. Rapid eye movements are often visible beneath a sleeper’s eyelids when REM sleep begins, and at that stage the person will be hard to waken and will lose postural control. For example, a sleeping cat will slip from sitting to sprawling.
However, to score sleep stages more accurately it is necessary to follow the routing of the AASM (American Academy of Sleep Medicine) manual systematically. You learn a lot from this overview and its follow-ups here, there, and yonder. The emedicine website requires free registration, but no ads will penalize you for registering as far as I’ve noticed. Notice that along with brain waves, the EEG includes artifacts that you will not be interested in, which are illustrated here and there.
Even with training, though, people disagree sometimes about the stage of sleep that is shown in a 30-second sleep epoch. Psychologists calculate the interrater reliability to judge the variability in people’s scoring, and the agreement among sleep scorers is a little above 80 percent, which is deemed acceptable. However, the kappa statistic, which measures scoring agreement that is not due to chance, is well below the percentage of agreement, making some sleep experts willing to rely on automatic scoring.
If you looked at some of the EEG examples, you can appreciate why sleep technologists make a good living, not to mention that it’s hard to escape night shifts. However, even a sleep expert won’t give a hard and fast answer to the question of how much sleep each person needs. The answer is always “It depends”. You can make your sleep more efficient by sleeping next to your partner and staying asleep 80 percent of the time when you’re in bed, avoiding interruption of stages 3 and REM sleep.
No electronic device will tell you whether you’re sleeping well, but that’s what the Pittsburgh Sleep Quality Index is for. You can find the details there. It’s apparent that sleep quality depends as much on other people’s expectations, like work schedules, as your own behavior.
SOCIAL: Even at a social level, there is a lot about circadian rhythms, including sleep, that an app won’t address, though the information from sleep trackers may help us to adapt (see sidebar) to society’s demands. Sleep customs vary with culture and with history. Sleep hasn’t always been regarded as we do now, as an 8-hour continuous exercise that is often impossible to achieve and may not match what suits us. In our prehistory the nighttime was a dangerous time and may have required much lighter sleep for some folks. Even a couple of centuries ago many Europeans slept in two segments, as the Mattress Nerd entertainingly describes. And children’s bedtimes still vary around the world.
There is general, and perhaps obvious, agreement that human sleep habits evolved as we lay upon leaves, and Sealy has (or have—this is the British branch speaking) confirmed that leaves were our first mattresses. A tree limb might have served as a mattress before that? But “no primate more than 30 kg sleeps on a branch.”
Even the entirely fictional Frankenstein’s creature aspired to repose upon a bed of leaves, but anyone who knows mattresses knows that that would have been just the start, and at least two university faculty are relieved that a line of little Frankenstein creatures never got started in reality.