Researchers have now identified five distinct stages of sleep.
Soon after nodding off you drift into the creatively labelled ‘Stage 1’. Here your brain is still very active and producing high frequency brain waves known as ‘Alpha’ waves. During this stage people frequently experience two types of hallucinations known as hypnagogic imagery (which occur when people are drifting into sleep) and hypnopompic imagery (which occur when they are waking up).
Either type can result in a wide range of visual phenomena, including random speckles, bright lines, geometric patterns, and mysterious animal and human forms. These images are often accompanied by strange sounds such as loud crashes, footsteps, faint whispers, and snatches of speech. Interestingly, these are exactly the type of experiences that have been mistaken for the presence of a ghost for hundreds of years.
Having survived the potential terrors associated with ‘Stage 1’ you drift into ‘Stage 2’. Again, your brain is far from calm, often producing brief bursts of activity known as ‘spindles’. ‘Stage 2’ lasts for about 20 minutes and can result in the occasional mumble and even full on sleep-talking. Slowly you drift further down into, you guessed it, ‘Stage 3’. Now your brain and body are starting to become properly relaxed and after another 20 minutes or so you finally enter the deepest stage of sleep . . . In
‘Stage 4’, your brain activity is at a minimum, resulting in very slow moving ‘Delta’ waves. If you are going to engage in a spot of bedwetting or sleepwalking, this is the moment.
After around 30 minutes or so in ‘Stage 4’ something very strange happens. Your brain moves rapidly back through the first three stages and then enters a mysterious state. It exhibits the same high levels of activity originally displayed during ‘Stage 1’, but your heart races, your breathing becomes shallow, and you produce the REMs that so fascinated Aserinsky all those years ago. Now you are dreaming. Everyone experiences this REM stage about five times each night, with each of the periods lasting an average of twenty minutes. Although some people think that they don’t dream, if they are woken up directly after exhibiting REMs, more often than not, they will report a dream. It is not that some individuals don’t dream, but rather that they don’t remember their dreams in the morning.
Additional work has shown that two curious things happen to your body when you dream. First, your genitals become active, with men getting an erection and women exhibiting increased vaginal lubrication. Although hailed as a breakthrough in the 1960s, some researchers have argued that the effect may have been discovered long before, pointing out, for example, that one of the 17,000-year-old cave paintings in Lascaux depicts a dreaming Cro-Magnon hunter with an erect penis (then again, he might just have really enjoyed hunting). Second, although your brain and genitalia are very active during dreaming, the rest of your body is not. In fact, your brainstem completely blocks any movement of your limbs and torso in order to prevent you acting out your dreams and possibly hurting yourself.
Just as your brain can fool you into seeing an afterimage of a ghost, it can also trick you into thinking that you have encountered an evil entity. As you move between ‘Stage 1’ and the REM state your brain sometimes becomes confused, causing you to experience the hypnagogic and hypnopompic imagery associated with ‘Stage 1’, but the sexual arousal and paralysis associated with the REM
state. This terrifying combination causes you to feel as if a heavy weight is sitting on your chest and pinning you to the bed, sense (and sometimes see) an evil entity or two, and believe that you are having a rather odd form of intercourse.
For centuries a significant percentage of the public have convinced themselves that they have been attacked by demons, ghosts and aliens. Not only have sleep researchers revealed the true nature of such experiences, but also uncovered the best way of banishing these entities from your bedroom.
Perhaps not surprisingly, this does not involve extensive chanting, the sprinkling of holy water or an elaborate exorcism. In fact, it turns out that all you have to do is try your best to wiggle a finger or blink. Even the smallest of movements will help your brain shift from the REM state to ‘Stage 1’ of sleep, and before you know it you will be wide awake and safely back in the land of the living.
Those who believe in ghosts have now been forced to accept that the incubus experience is not evidence of hell, but rather a clever trick of the mind. However, rather than jettison their belief in hauntings, they have focused their attention on an altogether trickier problem – the many ghost sightings that happen when people are far from sleep.
HOW TO SUMMON THE SPIRITS
Would you like to see a ghost right now? If so, stare at the small white dot in the left-hand box below for about thirty seconds, and then look at the small black dot in the empty right-hand box.
After a few moments you should see a mysterious woman in white emerge in front of your eyes.
If you repeat the exercise, but look at a white wall rather than the tiny box, you will see a giant ghost projected onto the wall.
Psychologists refer to the ghostly figure that you just saw (and that many of you will continue to see for the next few minutes - sorry about that) as an 'afterimage'. Your perception of colour is based on three systems. Each of these systems is based around two colours, with one dealing with the red-green continuum, another with blue-yellow and the third with black-white. In each of these systems the two colours oppose one another and can't be seen together. For example, already in a quiet state, the activation made them become over-excited, creating a rebound effect
that resulted in a white afterimage.