This error was corrected in the A2 Mini Companion (page 8): More darkness means more melatonin, and more melatonin means less serotonin (because melatonin is produced from serotonin). Low levels of serotonin are associated with depression.

The story starts with blind people – some blind have considerable difficulties with their circadian rhythms because their insensitivity to light means that their body rhythms are constantly fluctuating. However, this is not true of all blind people. It seems that the eye has special light receptors related to the circadian rhythm and these feed directly into the SCN (Czeisler et al., 1995). Other research has found that these special cells are particularly sensitive to blue light. For example Kayumov et al. (2005) found that volunteers doing simulated shift work had reduced melatonin production if they were exposed to bright light but not if they wore goggles that filtered out blue light. Dim lighting also did not result in reduced levels of melatonin.

You may ask ‘Where did the melatonin come in’? Light resets the SCN and also suppresses the production of melatonin (when it gets dark, melatonin levels rise making us sleepy). Suppression of melatonin has been linked to cancer, obesity, diabetes and cardiovascular disease. So shiftworkers doing night work with bright lighting are exposed to risks that could be prevented if the lighting was dim or blue light was filtered out. In fact the same is true for all of us, at night it is better to sit in dimly lit rooms and use lighting with less blue in it.

The data for the graph was taken from a study Lyamin et al. (2004) of one dolphin, reported by the Phylogeny of Sleep Project (you can see the dolphin data here). As pointed out in our textbook much of the data about sleep is actually derived from very small samples and research conducted under poorly controlled conditions.

All of the other dolphin studies given by the Phylogeny of Sleep Project did not record the amount of REM sleep which is why we used the data from Lyamin et al. However this data is misleading as the general view appears to be that (REM) sleep is either absent in cetaceans (e.g. dolphins) or occupies an extremely small proportion of the day – an absolute maximum of 15 min each day (Manger et al., 2003). In fact a recent paper published by Lyamin et al. (2008) states that ‘We find that for cetaceans sleep is characterized by USWS [unihemispheric slow wave sleep] [and] a negligible amount or complete absence of rapid eye movement (REM) sleep’.

Might this also apply to older childern and adults? That would be interesting to know!
Annie Bernier, Stephanie M. Carlson, Stéphanie Bordeleau, Julie Carrier. Relations Between Physiological and Cognitive Regulatory Systems: Infant Sleep Regulation and Subsequent Executive Functioning. Child Development, 2010; 81 (6)

Fred Rieke, Timothy M. Brown, Carlos Gias, Megumi Hatori, Sheena R. Keding, Ma’ayan Semo, Peter J. Coffey, John Gigg, Hugh D. Piggins, Satchidananda Panda, Robert J. Lucas. Melanopsin Contributions to Irradiance Coding in the Thalamo-Cortical Visual System. PLoS Biology, 2010; 8 (12)

Writing in the journal Nature, researchers said they have developed a system capable of recording higher-level brain activity.

“We would like to read people’s dreams,” says the lead scientist Dr Moran Cerf.

The aim is not to interlope, but to extend our understanding of how and why people dream.

However, a word of caution is now being given about such therapy as a meta-analysis of over 12 years’ Canadian data suggests that the costs of such treatment might outweigh the benefits. The issue is that these treatments seem to be associated with a significant increase in mortality rate from 10.5% to 15.7%.  This is still a low risk of dying, but it does represent an increase if using the medication of about 36% compared to not using medication when other variables are factored in.  The data came from more than 14.000 adults between the ages of 18 and 102, and extraneous or confounding variables such as smoking, alcohol use, general health and physical activity were controlled for.

Why is there such an increased risk of dying when using these drug therapies? It is known that sleeping pills and anti-anxiety drugs all slow reaction times, alertness and coordination, so increased falls may be a partial factor. These drugs could also depress the respiratory system enough to cause or trigger breathing problems during sleep. And as these medications also inhibit some CNS function,  judgement may be affected, which could increase suicidal behaviours. CBT has been shown to have good results in treating people with insomnia and anxiety disorders, and this psychotherapy does not carry an increased risk of dying, so the research suggests that perhaps this could be combined with cautious use of drugs after discussion between doctor and patient.

Belleville, G. Mortality Hazard Associated With Anxiolytic and Hypnotic Drug Use in the National Population Health Survey. Canadian Journal of Psychiatry, 2010; 55 (9)

• adolescents who cut down on sleep risk an increase in body weight, and
• sleeping less than 6-8 hours a night leads to a 12% increase in the risk of dying early, and
• even short periods e.g. one night of very reduced sleep can lead to resistance to the hormone insulin and potentially to developing type 2 diabetes.

These studies’ conclusions do not, however, mean that a few nights of reduced sleep will make you fat, develop type 2 diabetes or die in the near future; the message seems to be that 6-8 hours sleep a night is not just the norm, but really, really good for us !

In 2008 in the UK a middle aged man with a long history of sleep disorders actually killed his wife whilst they were both asleep. This tragedy happened when they were on holiday and the man in question had decided not to take his medication. He had a nighmare, thought he was struggling with assailants, but when he woke he found his wife dead. There is no reason to suspect that the couple were not happy together, and sleep disorder experts and the police accept that this unhappy case is one of temporary  “insane automatism”.