Sleep is a funny kind of behavior--the more effort you put into getting it, the more elusive it becomes. We spend more time at that activity--well, inactivity--than at anything else we do in life (aside from breathe, perhaps). So many things can go wrong with sleep.
If you're just looking for advice about how to sleep better, best to check elsewhere. Read on if you want to get the big picture about sleep as a kind of behavior that we perform both for pleasure and out of necessity, and to consider what sleep disruptions can teach us about behavior in general. As will become evident, I hope, over the next few essays, there are common links in sleep, sex, and eating that show a lot about what makes us tick.
What makes us sleep? Obviously, we sleep because we're tired-when we've been awake for 16 hours or so, sleep just seems more and more attractive. But why stay up for 16 hours and sleep for 8? Why not sleep 1 hour, get up for 2, ad infinitum? Some cultures play with the 16/8 arrangement-- in Latin countries, you might take an afternoon siesta and then stay up later at night--but by and large sleep patterns for people worldwide tend to stick to a limited number of patterns, no matter where they live. So the other major driving force for sleeping all night and staying awake all day, beyond mere tiredness, is our hormonal biological clock. Melatonin is a key player. The pineal gland, that funny little nubbin that Descartes famously mistook for the seat of the soul, puts out melatonin like clockwork to send us to bed at night and keep us there till morning.
You might equate sleep with shutting down--darkening the monitor and spinning down the hard drive--but sleep requires active brain processes to maintain slumber. Where there are moving parts there can be broken parts. Thus narcolepsy, for example, is a true disorder of sleep regulation due to a dysfunction of these hormonal mechanisms that renders a person vulnerable to frequent plunges into sleep by day, despite having experienced adequate sleep at night.
Some sleep-related problems come from a blockade of opportunities to sleep. Lack of sleep affects not only the drive to sleep, but also arousal in general. In the initial phase of sleep deprivation a person often experiences erratic surges of arousal and brownouts into lethargy throughout the day. Ongoing forced sleep deprivation diminishes the capacity to sustain attention or to modulate emotional arousal. Ultimately the drive to sleep overwhelms other salient drives; if you stay awake long enough, you'll sleep no matter how hungry you are. Extreme sleep deprivation causes such potent distress that it has frequently been employed as a method of torture.
From this perspective, obstructive sleep apnea, a common disorder of sleep often associated with profound problems with mood and cognitive functions, is a form of self-imposed torture. The mechanism for the inability to maintain a deep sleep in sleep apnea begins with airway constriction that emerges when the muscles surrounding the airway relax with the onset of deep sleep. Imagine if every time you nodded off, someone came and cut off your air supply--how long would you remain asleep while holding your breath? The carbon dioxide that accumulates whenever you hold your breath jolts the brain into action, waking the person before the benefits of sleep can be enjoyed.
Sleep is a motivated behavior. People have not only a need for sleep, as they have for breathing, but also a desire for sleep and a fear of not being able to sleep. Sleep thus involves complex behaviors beyond simply lying down and shutting one's eyes. Good sleep depends on a desire for sleep. Satisfying sleep rewards and reinforces behavior that leads to it. The anticipated pleasure of comfortable rest facilitates sleep by inducing a state of relaxation.
Conversely, in a state of mind where the pleasure response is impaired, as in a depressive syndrome, the failure of the pleasure response contributes to the common symptom of chronic insomnia. When a person with depression can sleep, it is rarely satisfying, even when done to excess. Thus not only will a depressed person feel drawn back to bed simply because there seems to be no motivation to get up, but bed itself is not the island of relaxation it ought to be. Hence upon hitting the sheets the depressed person loses that soothing sense of "ahhhh" that helps us drift off to slumberland when we're fortunate enough not to suffer from depression or insomnia.
A person may become conditioned to experience insomnia if bed becomes a trigger for arousal, not relaxation. This can be a product of habit when a person conducts intensive, high-stakes work on a laptop just before turning off the lights or enjoys watching action movies late into the night. When a person has, for whatever reason, struggled to fall asleep for some time, bed no longer suggests pleasure. Without the pleasurable anticipation of sleep, it is more difficult to induce the state of relaxation and diminished arousal that brings it on. The result is a self-perpetuating problem with insomnia.
So, restful sleep begets the anticipation that sleep will be satisfying, which begets restful sleep, and so on. Mess with that cycle at your peril.
