Why do we dream? Japanese researchers believe they may have found the answer – to give our brains a refresh.
A team from the University of Tsukuba have found intriguing new evidence of brain refreshing that takes place during a specific phase of sleep: rapid eye movement (REM) sleep, which is when you tend to dream a lot.
What is happening in the brain when we dream?
It looks like the body is using dreamtime to enrich the grey matter with better blood flow. Using a dye to make the brain blood vessels visible under fluorescent light, with a technique known as two-photon microscopy the researchers could directly observe the red blood cells in capillaries of the neocortex in non-anaesthetised mice and measure electrical activity in the brain to identify REM sleep, non-REM sleep, and wakefulness. They also looked for differences in blood flow between these phases.
Lead researcher Professor Yu Hayashi commented: ‘There was a massive flow of red blood cells through the brain capillaries during REM sleep, but no difference between non-REM sleep and the awake state, showing that REM sleep is a unique state.’
The research team then disrupted the mice's sleep, resulting in ‘rebound’ REM sleep, a stronger form of REM sleep to compensate for the earlier disruption. Blood flow in the brain was further increased during rebound REM sleep, suggesting an association between blood flow and REM sleep strength.
However, when the researchers repeated the same experiments in mice without adenosine A2a receptors (the receptors whose blockade makes you feel more awake after drinking coffee), there was less of an increase in blood flow during REM sleep, even during rebound REM sleep.
It’s believed that adenosine A2a receptors may be responsible for at least some of the changes in blood flow in the brain during REM sleep.
Given that reduced blood flow in the brain and decreased REM sleep have been linked with the development of Alzheimer's disease, which involves the build-up of waste products in the brain, further research may look whether increased blood flow in the brain capillaries during REM sleep is important for waste removal from the brain.
Can dreaming help alleviate stress?
This also indicated that this brain refresh which occurs during REM sleep, means dreaming can have a big role in how we process stressful events.
During the lockdown for COVID-19 for example, sleep experts noted a big upsurge in reports of vivid and sometimes downright weird dreams.
According to dream expert and psychologist Ian Wallace, he noted an upsurge in people getting in touch from China as far back as January.
‘Lots of people were finding their sleep disturbed by intense and often frightening dreams,’ he recalls. ‘Then, as COVID-19 spread, I began hearing from people in Italy, the US, South America and the UK. Clients both old and new were reporting dreams and nightmares which were more distressing than anything they’d ever experienced before.’
So, what do these vivid dreams mean? Professor Colin Espie, professor of Sleep Medicine at the University of Oxford believes our dreams reveal how stressed we are, hence the pandemic increased reports of strange dreams: ‘One thing that is difficult for us to manage as human beings includes uncertainty, therefore, that’s the kind of emotion that is a part of the reality for us right now,’ he comments.
How to remember your dreams
Wake up gently and you have more chance of recalling your dreams. Before lockdown, many of us were slaves to our alarm clocks. One theory is, that when you're awoken by the ringing or beeping from clocks, you’re less likely to remember what you’ve been dreaming about. A study of 1,251 working adults in the UK in April 2020, found a third of us are no longer set an alarm to wake up – so that would go some way to explaining why so many of us have recalled these strange dreams and nightmares over the past 18 months.
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