Posts archived in Biological rhythms and sleep


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SAD, melatonin and serotonin

July 25, 2011 by .

Juliette Massey-Smith wrote in the following query: I was wondering if you could help… I was re-reading about SAD in your AQA textbook and read on p.4 that in winter melatonin and serotonin are higher and this causes depression, but then also that LACK of serotonin causes it… What am I missing?

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.

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Blue light bad

May 27, 2011 by .

Early temporal isolation studies overlooked the fact that artificial light has an effect on circadian rhythms but more recent research showed that even fairly dim lighting may reset the SCN (suprachiasmatic nucleus). Even more recently research has found that blue light is particularly effective – for good and bad.

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.

 

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It seems that dolphins don’t dream

January 25, 2011 by .

In Chapter 1 (Biological rhythms and sleep) of our A2 Complete Companion there is a contradiction (kindly pointed out by Ruth Bailey of Akeley Wood School). On page 13  the text says that dolphins don’t have REM sleep whereas on page 14 the graph indicates a significant amount of REM sleep in dolphin. So which is correct?

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’.

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Is it when you sleep, not how much, that counts?

December 14, 2010 by .

A small study of Canadian infants and toddlers found that those who slept most at night were making significantly more progress in executive functions than those who slept less at night, even if the latter group also had daytime sleep. These functions include impulse control, memory and mental flexibility. The researchers controlled for parents’ education and income and children’s general cognition, but the link between night-time sleep and development of cognitive skills remained. These finding support similar research findings on schoolchildren.

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)

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How the SCN sees light

December 8, 2010 by .

It’s been known for ages that information on light levels is passed from the two retinas via a special small nerve from each eye to the SCN, but the mechanism of this is now more clear. As well as rods and cones, cells which are sensitive to light and give us black-and-white and colour vision there is a third type of light-sensitive retinal cell. These are far less in number than rods and cones, and react to light by expressing the pigment melanopsin, so they are known as mRGCs (melanopsin-expressing retinal ganglion cells). Not only do these cells send information to the SCN but they also control pupil size. And now it seems they also contribute to our visual image formation as axons from the mRGCs have been traced onwards from the SCN to visual processing centres. What does this imply? It gives some idea of how seriously sight impaired people can still detect levels of brightness, plus the possibility in the future of engineering melanopsin-expressing cells to improve or restore sight.

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)

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Measure your dreams

October 29, 2010 by .

A US researcher has said he plans to electronically record and interpret dreams.

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.

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Costs and Benefits of Drug therapy

September 14, 2010 by .

Insomnia and anxiety disorders are very different problems, each making normal, everyday life difficult, and drug therapy can usually help with both of these conditions.

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- Read the rest of this entry »

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Sleep in order to live long and prosper

May 6, 2010 by .

Recently published sleep research suggests that

  • 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 !

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To sleep, perchance to dream … or commit murder?

February 16, 2010 by .

Some sleep disorders are well known – sleep-walking for example. But in very unusual cases people who sleepwalk behave in a highly unusual way, this is a very rare form of the disorder somnambulism when they commite violent acts.

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”.

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Core and optional sleep

September 22, 2009 by .

I have been sent a query about core and optional sleep as there is some contradiction between what we said in the 1st and 2nd editions of the A2 Complete Companion. Looking around the other A2 textbooks, there seems to be a wide variety of explanations – most of which are not correct. Jim Horne proposed the concepts of core and optional sleep as a different perspective to the REM/non-REM distinction, which means that it is not possible to say the core sleep includes or doesn’t include REM sleep. Horne’s concept was that core sleep is essentially the first hours of sleep, and thus refers to mainly slow wave sleep (SWS) but includes some REM sleep. As the night progresses there is less SWS sleep and more REM sleep. Optional sleep is the sleep that occurs later in the night and which appears to be less crucial. This consists mainly of REM sleep but has some SWS/non-REM sleep. I hope that is clear! Thanks to Jo Haycock for pointing the inconsistency out to me.

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