Every night, we shut our eyes, let the mind slip its moorings, and enter the blank Iimbo of sleep. While it is tempting to treat sleep simply as a state of unconsciousness, psychologists tell a very different story in which sleep is really not as far from waking as it first appears.
Being asleep seems to give us a glimpse of what it would be like to be dead. Sleep undoubtedly appears to extinguish the light of experience, even if our slumber is sometimes fitful or perturbed by the odd dream or nightmare. However, sleep research shows that our repose is a surprisingly active affair in which consciousness is never really switched off. Brain recordings reveal that we spend each night alternating between two very distinct types of sleep – the deep, steady electrical rhythm of slow-wave sleep (SWS) and the frantic buzz of REM sleep (so-called for the rapid eye movements in which the eyeballs seem to chase phantom visions). We begin each night in SWS. At first, this is so deep that we are practically comatose. Then, after about 90 minutes, there comes a brief interruption of REM, which lasts about 10 minutes. As the night goes on, the switch over between SWS and R..EM continues to occur every 90 minutes or so, but the REM periods get much longer, and the SWS periods become progressively shallower. On average, we spend about one-quarter of every nig ht in REM sleep.
The dreaming brain
When REM sleep was first discovered in the 1950s, it was thought to be the only sleep phase in which dreams occurred. However, it has since been found that mental activity of a sort goes on all night long. Even subjects roused from SWS usually report vague ruminations. US psychologist David Foulkes describes these slow-wave dreams as drowsy thoughts rather than bright images, and, despite their hazy character, their existence shows that the mind muses to itself all through the long hours from dusk to dawn.
Sleep researchers have concluded that the brain never actually shuts down at night. Brain cells have no ‘off’ switch, and indeed, they must fire a few times each second to stay alive and healthy. So, instead of turning its engines off, a better analogy would be that the brain puts itself into neutral when it enters SWS. It puts a block on incoming sensations, pre venting external sights and sounds from troubling the mind, and it suspends short-term memory. The resulting state of consciousness is confused and disjointed, and any thoughts or images evaporate just as fast as they form.
In REM sleep, the brain switches m to quite a different state. Activity in the brainstem is inhibited, temporarily paralyzing the body. This essential safety mechanism ensures that dreams are not acted out physically. Then, for some reason, the brain erupts into a succession of vivid, internally generated imagery. However, the block remains on short-term memory, and so the conscious self cannot fix what is going on. In a confused way, it tries to make sense of the random images, but it never really catches up with them. And any story it spins is usually quickly forgotten on waking.
Functions of sleep
SWS seems to be essential for growth and maintenance, but the purpose of REM sleep is harder to explain. It has been suggested that REM sleep is simply nature’s way of keeping us nearly awake, but out of mischief, until morning. Vivid dreams – the subject of conjecture for centuries – may be merely by-products of a slumbering consciousness.
Conscious Aspects Of Sleep
Looking at mental functioning while awake and in REM sleep yields some interesting comparisons:
- While awake, our thoughts and intentions are generally clear and directed, but in REM sleep, they are confused and illogical.
- Perception is strong in both states, although in REM sleep, it is directed towards internally generated sensations rather than to the external world.
- Memory is also strong in both states, with more distant memories rather than recent ones typically dominant during REM sleep.
- Instinct is a strong influence in REM sleep, whereas in waking, it is mediated by rational thinking.
Sleepwalking
Most of us know someone who walks or talks in their sleep, but some sleepwalking stories are truly bizarre. One woman packed her dogs into her car and drove 20 miles before waking up; another stumbled off the balcony of her holiday hotel, fell 15 feet, and did not wake up until she reached the hospital. Our capacity to behave unconsciously while asleep is even recognized in law – several individuals have been cleared of attempted rape or murder because they were ‘asleep’ at the time.
Researchers have found there is a clear difference between ordinary sleepwalking and a more specific REM sleep syndrome. Ordinary sleepwalking happens in deep, slow-wave sleep. We come awake enough to act on automatic pilot – to get up and do something routine like go to the toilet or perhaps even take the car for a midnight spin. However, murders and other violent acts must occur in the high arousal of REM sleep, so the usual REM paralysis, the brainstem block on muscular activity that normally prevents us from acting out our dreams, is somehow absent in these cases. On closer examination of such people, doctors often find evidence of a degenerative disorder like Parkinson’s disease affecting the brainstem.
