March 11, 2013 by Cara Flanagan.
There are many theories about why we sleep and dream, and many of these involve memory in some way (including Freud’s theory of why we dream). A relatively recent theory has been gathering support, variously called synaptic renormalisation hypothesis or synaptic homeostasis hypothesis (aka ‘SHY’ – first proposed by Tononi and Corelli, 2003).
The basic principle is the suggestion that sleep provides a necessary opportunity for brain synapses to recover. During the day we are constantly forming new memories – when a new memory is formed essentially the synapse between the neurons involved becomes strengthened. Such strengthening can’t go on forever because of the energy required. So, according to SHY, slow wave sleep provides a slowing down of brain activity in order to allow all synapses to reduce activity. The relative differences in strengths between neurons remains, so the new memories aren’t lost.
Not everyone supports this idea. For example Frank (2013 here) argues that the underlying mechanisms have yet to be clearly defined and, until this happens, the hypothesis remains tentative.
Subscribers to the New Scientist can read about this hypothesis, and more, in a great piece on the Wonder of Slumber (2 February 2013).
July 30, 2012 by Cara Flanagan.
In our A2 Complete Companion we reported a study by Knutsson et al. (1986) who found that shift workers were three times more likely to develop heart disease than non-shift workers. A study just published by Hackam et al. (2012) confirms this, claiming a 24% increased risk of a coronary event and 5% increased risk of stroke. The study controlled for socioeconomic status, diet and general health of the workers.
It may be that problems arise because of poor day time sleeping and disruption to eating patterns and social routines. This might be improved by ensuring that shift workers have a minimum of two full nights’ sleep between after a period of night shifts, and should do both day and night shifts for alternate periods. See here for more detail.
February 22, 2012 by Mike Cardwell.
Today’s BBC website carries a fascinating article that challenges the commonly held view that an eight-hour period of continuous sleep is natural for human beings.
We often worry about lying awake in the middle of the night – but it could be good for you. A growing body of evidence from both science and history suggests that the eight-hour sleep may be unnatural.
In the early 1990s, psychiatrist Thomas Wehr conducted an experiment in which a group of people were plunged into darkness for 14 hours every day for a month.
Read the rest of this entry »
January 25, 2011 by Cara Flanagan.
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’.
May 6, 2010 by Evie Bentley.
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 !
February 16, 2010 by Evie Bentley.
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”.
September 22, 2009 by Cara Flanagan.
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.