It intrigues me that scientists are no closer to understanding the main biological function of sleep than they were hundreds of years ago. Surely something so important to our health and wellbeing would be known inside and out by now?
Apparently not. It is still as great a mystery as ever.
Whilst doing my usual trawl through databases to find interesting research for our blog readers, I came across an article on a new hypothesis for why we sleep; to refuel energy stores in our brains. Well that makes sense, doesn’t it? I certainly know how my brain operates without enough sleep. The article claims that contrary to popular belief, sleep is not about resting the body. Consensus now is that sleep mostly does something for the brain.
Over a decade of research has given us details about what happens during sleep, but not a lot of information as to why. REM (rapid eye movement) sleep is the active phase during which we dream, but we spend about 80% of our time in non-REM sleep, where our EEG (electroencephalogram) readings produce a higher amplitude and lower frequency result. (Interestingly echidnas do not go into REM sleep, as opposed to most other mammals that have about as much time in it as we do.)
Apparently, there are more theories out there about sleep than could possibly be correct, and there is evidence for and against most of them. However, prominent researchers, Bennington and Hellar, from Stamford University put forward a compelling case that the main function of sleep is to restore glycogen levels in the brain (glycogen is a storage form of glucose). They propose that when the brain starts to feel its energy reserves depleting, it produces a substance called adenosine. Interestingly caffeine and theophylline (a substance in tea) inhibit adenosine receptors.
The pieces are starting to fit together.
How might adenosine work? Hellar hypothesises that when enough adenosine molecules bind to receptors in the brain, it causes the neurons (brain cells) to fire in synchronicity and at a slower rate which results in non-REM sleep. He likens it to a choir singing the same song, as opposed to being awake, where neurotransmitters such as serotonin and norepinephrine keep the neurons constantly firing in what he calls ‘static sounds and discordant voices.’
Further research is needed, but if their theory proves to be correct, it will be an interesting breakthrough in our scientific understanding of sleep.
References available upon request