Have I got Snooze for you? A Review
Posted by Science Oxford on September 5, 2011 | comments
Talk review by Blanka Sengerová
Sleep is something that influences all our lives. From the struggle to get up on Monday mornings to coping with jet-lag, the body has to carefully balance our need to be alert or to be at rest. But how does the brain control this? How much sleep do we really need? Why do flamingos sleep on one leg? These were the questions that were addressed by Dr Peter Oliver, a researcher who is interested in how genes and environment influence human sleep, particularly in relation to disease. During his talk at Science Oxford, he took the audience on a tour de force of many sleep-related issues, ending in a very lively Q&A session to round off the evening.
First of all, why is sleep so important? Apparently, although only about 50 calories are saved by an average human when sleeping compared to sitting down and resting, sleep is key for enabling brain recovery. This can easily be demonstrated by the problems that arise when lack of sleep is encountered; indeed, Dr Oliver pointed out that in cognitive tests, those who have had no sleep for 17 hours have similar levels of ability as those who have drunk two glasses of wine. And whilst you probably wouldn’t (and certainly shouldn’t) drive after drinking two glasses of wine at the pub, you wouldn’t think twice about doing so when you’ve just done a monster of a day in the office, the lab or the operating theatre from 7am till midnight, yet you might be as likely to cause an accident in the latter as in the former case. In a similar vein, experiments have been carried out to show that sleep helps to consolidate memories acquired during the wakeful hours: when you practice doing a simple task such as tapping out a sequence with your fingers, you get faster and faster at doing it, eventually reaching a plateau where you cannot get any faster. It has been shown that if a night’s sleep follows the learning period, the level of the plateau can be increased.
What are the phases of sleep? Dr Oliver explained that during an average night, the type of sleep that we go through changes as the night progresses, as can be illustrated by something called a polysomnogram (as shown below, taken from http://en.wikipedia.org/wiki/Sleep).
Early in the night, we go through a phase of deep sleep, during which our brain recovers and regenerates, with heart rate and body temperature lowered and brain activity at a minimum. This is then followed by a phase of REM (rapid eye movement) sleep, during which the brain is active (but the muscles remain completely paralysed), allowing you to experience dreams. These two phases alternate throughout the night, usually 4-5 times or so, with the deep sleep sections becoming progressively shorter and the REM sleep sections becoming gradually longer. Interestingly, if you’ve been drinking a lot of alcohol, you may fall into deep sleep very quickly (the unconscious feeling of those after a night out) and remain in it for a while, but after this, you never return to the deep stage again and oscillate between levels close to the REM and wakeful level, meaning that the night’s sleep isn’t really as restful as it would be with a greater number of deep sleep phases.
The next chapter in the evening’s tour of sleep was about how we sleep. Apparently 1000 people were filmed in their sleep to give us an idea of the position in which people prefer to sleep. Dr Oliver explained how this research, according to him rather disdainfully published in the “high quality journal that is the Daily Mail”, suggested that the position you sleep in (mostly one of the following six: foetal, log, yearner, soldier, freefaller, starfish) says something about your personality. Although at the time, in 2003, the research by sleep researcher Chris Idzikowski was widely reported in the popular press, and although he has a large number of sleep related publications listed on PubMed (a repository for peer reviewed scientific articles), I have been unable to find a reference to this particular study so it appears never to have been published in a peer-reviewed journal, meaning that it is healthy not to succumb to the hype and remain a little sceptical until it is published and replicated by other researchers. However, whether or not your sleeping position says something about your personality, it is pretty certain that being comfortable whilst asleep is linked to the ability to have a good night’s sleep as serious insomniacs consistently seem to find it hard to get ‘comfy’ in their bed.
How much sleep do we actually need? These days, in the UK, the average amount of sleep people get is about 7 1/2 hours, which has been reduced by about 20 minutes over the last 20 years, perhaps due to the influence of the 24-hour-always-on-always-something-to-do society. According to the Guinness Book of Records, the longest voluntarily wakeful period record is held by Randy Gardner who, in 1964, managed to stay awake for 11 days, managing to still beat a scientist at pinball towards the end of his feat to prove that his cognitive abilities were not significantly impaired. More recently, in 2005, Tony Wright tried to and apparently succeeded at beating this record, but to his disappointment the Guinness Book no longer backs the sleep deprivation category due to its association with possible health risks. If an average human sleeps about 7-8 hours a night, how many do various animals need? In a spot of audience participation, a bit of guesswork ensued and afterwards Dr Oliver explained that animals such as pythons, sloths and others who can rest away from potential predators sleep for the longest periods, with hoofed animals such as pigs having a pattern similar to us humans and something like a giraffe or horse only being able to sleep about 2-3 hours a night, because of sleeping in standing position and most likely not being very comfortable. Meanwhile, something like a dolphin, flamingo or a duck doesn’t sleep at all and instead it basically shuts down one half of its body and brain, being able to rest one side whilst continuing to be aware of its surroundings in the ever changing environment with the other side. This is why you so often see flamingos on one leg as they are resting the other side!
It’s all well and good to know that sleep is absolutely essential for our cognitive abilities and brain function, but how does our body know when to sleep and when to be awake? The control of our sleep according to ~24 hour cycles is called the circadian rhythm and is affected by a number of external factors, including light, stress levels, diet and tiredness. All of these factors control the rhythm via a part of the brain called the SCN (superchiasmatic nuclei). The SCN ticks along, as it were, keeping an approximately 24 hour cycle and communicating the rhythm to the rest of the body and although the activity/inactivity cycle is very closely associated with the day/night pattern, it is interesting to note that in the absence of light cues, such as in a blind person, the SCN can take over and ensure that the 24 hour cycle is still followed (actually, to be entirely precise, the SCN, has a cycle of approximately 24.1-24.2 hours). In fact, when rare tumours affecting the SCN occur, the afflicted individuals have their body clock totally out of sync.
The synchrony between the SCN and the rest of the body is absolutely crucial for correct functioning, and the problems that occur may be exemplified by jetlag – if you find yourself in a different time-zone, your sleep patterns become very much out-of-sync with the daylight hours and even things such as your eating patterns might play tricks on you for a while. A demonstration based on drumming and the 4-beat rhythm showed us that when the SCN’s communication with the rest of the body (such as the liver) fails, the liver cells will still maintain an intrinsic rhythm by themselves but since there is no master beat control, they will gradually drift away from the rhythm set by the SCN. Interestingly, Dr Oliver raised the question of what happens to animals such as the reindeer in the far north where light/dark patterns change significantly with the changing seasons. Here, it turns out that a poorly acting SCN is actually an advantage, because the reindeer are able to adapt their active/resting periods according to the light/dark patterns more readily.
To round off the discussion of the SCN, Dr Oliver gave us a very brief explanation of how the SCN functions at the molecular level, using a negative feedback loop, like many other systems within the human body. In humans (and other mammals), the SCN produces two proteins called CLOCK and BMAL, which bind to the DNA molecule, the set of instructions that is used to produce proteins within the cells. As CLOCK and BMAL bind DNA, this results in the production of two proteins called PER and CRY (in analogy, if you grip the recipe book it means that you will be producing food). As more and more PER and CRY are produced, they themselves bind to CLOCK and BMAL, which disengages the CLOCK and BMAL from the DNA, stopping more PER and CRY from being made. These events occur in a rather exquisitely timed 24-hour cycle, allowing the characteristics of the SCN cells to change in time with this cycle, and thus form the basis of the rhythm master controller.
Finally, as Dr Oliver’s interest lies in the genetics of sleep, with particular emphasis on sleep related disease, he explained how sleep is a major part of neurological disease. Indeed, an early symptom of Parkinson’s disease is serious insomnia and mental health problems are also often associated with an inability to sleep. This may suggest the possibility that improving sleep may be a good early intervention that could be a cheap way of preventing or at least delaying the onset of these disorders. In fact, encouragingly a mouse model of Huntington’s disease showed improved brain activity when its sleeping patterns were improved. After whetting our appetite with these tidbits of knowledge and after a very interactive Q&A session, we certainly left the very stimulating lecture thinking that there is plenty more to research in the field of sleep genetics!
You can watch an interview with Peter Oliver and the webcast of the full talk is available here.
What do you think?