To sleep, perchance to clean

Heading back to his chambers after murdering Duncan, Shakespeare’s Macbeth hopes he’ll feel better after a good night’s sleep. “Sleep, that knits up the ravelled sleeve of care,” he said, though how anyone can sleep after just murdering someone is a bit of a mystery. But centuries later science has proved he was right – about sleep that is, not the murder. Ignoring the brain’s ‘stop’ signals allows toxins to build up in the brain and makes our bodies feel tired.

A study at the University of Rochester Medical Center (URMC) New York, published in October 2013 and intriguing entitled, ‘To Sleep, Perchance to Clean’, described how microglia cells (part of the brain’s immune system) clean the brain of cellular waste during sleep. Researchers found that a single protein called EP2 stopped the action of the microglia cells, and blocking this protein with a drug reversed memory loss and other Alzheimer’s like features in mice. Now a new study shows that this brain drainage is not just a night-time event, but needs to happen when we have been thinking hard to the point of fatigue during the day, too.

A new study from the Pitie-Salpetriere University Hospital in Paris reveals that when our brains are exhausted they release toxins into the prefrontal cortex, forcing the body to slow down to create time for the production of these toxins to cease and for them to be flushed out. We need to take a nap, according to the study’s author, Dr Mathias Pessiglione. He said, ‘our findings show that cognitive work results in a true functional alteration – accumulation of noxious substances – so fatigue would indeed be a signal that makes us stop working but for a different purpose: to preserve the integrity of brain functioning.’

The URMC research reveals that the brain’s unique method of waste removal, the glymphatic system, is highly active during sleep, clearing away toxins responsible for Alzheimer’s disease and other neurological disorders. Furthermore, the researchers found that during sleep the brain’s cells reduce in size, allowing waste to be removed more effectively.

Although we’re familiar with the old adage that our brains work better after a good night’s sleep, it’s a strange thought that exercising our brains hard can make our bodies feel tired. Sometimes our worries and stress prevent us sleeping well. There was a reported increase in Google searches on ‘insomnia’ during the Covid pandemic, for example.

Some years ago, I attended a lecture in Birmingham by an Israeli sleep neuroscientist who described the process and allowed time for questions and answers. My question was that if we couldn’t drift into sleep was it OK to take a sleeping pill? “Definitely,” he replied, adding with a smile, “I’m always asked that question.”

Dr Pessiglione warned that there are no shortcuts to stop your brain making you tired, with a nap during the day when this happens to you the only cure. Volunteers in the study made poor decisions and showed reduced pupil dilation, indications of being tired. They also had higher levels of a chemical called glutamate in the brain’s prefrontal cortex, a chemical which accumulates in the synapses between neurons, interfering with how messages are passed throughout the brain.

For those working in the office a hammock slung between desks could be the solution, while for those working from home half an hour on the sofa could do it. Unfortunately, most people ignore the signals from their bodies and push themselves through the stop signals, affecting the ability to make rational decisions and allowing toxins to build up in their brains. Don’t let your brain poison itself!