Seeking the science that lurks deep in our sleep

Sleep and dreams occupy a significant proportion of our lives and yet are poorly understood. We spend about one-third of our lives asleep and onequarter of this time dreaming.

We know since the 1950s that sleep occurs in five stages labelled one, two, three, four and REM sleep, each of which is characterised by a particular wave pattern on EEG measures. REM stands for Rapid Eye Movement as this is a key feature in this phase, along with paralysis of the skeletal musculature which prevents us acting out events in our dreams.

During a normal night’s sleep, we cycle through stages one to four and back through three and two to REM sleep over 90-minute periods. While dreams may occur at any phase of the cycle, they are most consistent and intense during REM sleep. If woken during the REM phase, we readily report having dreamed and remember the content quite well. Usually dreams are rapidly forgotten.

Sleep deprivation
If we are deprived of REM sleep, the body will tend to catch up when the opportunity arises, spending a greater proportion of sleep time in this phase. Sleep deprivation results in a deterioration of concentration, memory and general cognitive functioning. It is thought sleep serves two primary functions: repair and restoration of brain and body following a day's activity, and conservation of energy during this period of relative inactivity.

It has been hypothesised that REM sleep is important in facilitating memory storage. This is supported by the observation that ,following a new learning experience, time spent in REM sleep increases and people who increase it most remember new information best.

Another more unusual hypothesis regarding REM sleep is the rapid eye movement serves to agitate the eyeballs so as to increase oxygen to the corneas.

There are a number of conditions that result in sleep disturbance. Insomnia may occur as a consequence of loud noise, anxiety, pain, drugs, depression and various brain lesions. People with onset insomnia have trouble falling asleep; those with termination insomnia wake too early and can’t get back to sleep; while those with maintenance insomnia experience frequent wakening.

Sleep apnea is a condition in which breathing is disrupted during sleep. This is most common in overweight males when the airways are narrowed by excess pressure. It may contribute to some cases of sudden infant death syndrome.

Sudden collapse
Narcolepsy is characterised by frequent unexpected episodes of sleepiness during the day. These can be accompanied by cataplexy, an episode of total muscle weakness while the person remains awake. This results in sudden collapse and can be triggered by anger or laughter.

People with narcolepsy are more likely to experience sleep paralysis when going to sleep or waking up. This can be very frightening as the person is awake, but cannot move. They are also more likely to experience hypnagogic and hypnopompic hallucinations.

Hypnagogic hallucinations usually occur when going off to sleep and are commonly experienced as faces floating in the darkness and can sometimes be auditory with disembodied voices uttering meaningless sentences. Hypnopompic hallucinations that are experienced upon awakening tend to be very different. They are generally more intense with a strong sense of “a presence”, often malign.

Some people experience night terrors. These are far more severe and intense than bad dreams or nightmares. Night terrors occur during non-REM sleep and are experienced more in childhood. Sleep talking and sleep walking are other well-known, sleep-related phenomena.

Mythic monsters
In his recent book Hallucinations, Oliver Sacks postulates that our beliefs in the supernatural and the widespread descriptions of monsters, angels and devils across cultures might have their origins in the physiologically based experiences of hypnopompic images. It is estimated up to half of the general population have had such hallucinations.

While scientists struggle to understand sleep and dreaming, writers and artists entertain us with stories and creative imagery based on the experiences sleep provides. For a sample, try the current series of essays on dreams at the New York Review of Books blog at nybooks.com

Paul O'Donoghue is a founder member of the Irish Skeptics Society Contact@irishskeptics.org