Dr's Casebook: Fruit flies research reveals the importance of deep sleep

Over the years I have written several times about medical research carried out using fruit flies.

Saturday, 23rd October 2021, 4:45 pm
Fruit flies research reveals the importance of deep sleep. Photo: Getty Images

Over the years I have written several times about medical research carried out using fruit flies.

They have been of inestimable value over the decades, leading to the development of many drugs, the elucidation of various genetic problems and the unravelling of many mysteries of physiology.

Indeed, at least two Nobel prizes for medicine and physiology were won using studies on fruit flies.

A recently published study that has looked at the brain activity of fruit flies and also their behaviour has demonstrated that deep sleep has an ancient restorative power to clear waste product from the brain.

This is actually a very important subject, because that waste may include the sort of toxic proteins that may lead to neurodegenerative disease, including dementia.

You may not think that we humans have much in common with these small insects that measure less than three millimetres in length. In fact, the neurones in the insects’ brains that govern their sleep and wakefulness cycles are amazingly similar to those of humans.

Sleep is generally divided into two stages, rapid eye movement sleep (REM) and non-rapid eye movement (NREM). Non-rapid eye movement sleep is further split into three parts, starting to fall asleep, light sleep and deep sleep.

During a typical night, your sleep alternates through cycles of rapid eye movement and non-rapid eye movement sleep about every 90 minutes. Ideally, you want to achieve five or six full sleep cycles, the equivalent to seven and a half to nine hours of sleep each night.

Fruit flies exhibit proboscis extension sleep (PES) when they are in deep sleep. It is similar to our deep sleep. During this stage fruit flies repeatedly extend and retract their proboscis or snout.

The scientists think this pumping movement circulates fluids from the brain to their version of the kidneys. Effectively, it clears brain waste. They have actually demonstrated that this does clear waste and aids injury recovery.

They conclude that deep sleep serves a role in waste clearance in the fruit fly and that it indicates that waste clearance from the brain is an ancient evolved function common to all creatures that sleep. It highlights the importance of getting good quality deep sleep, because it is during this sleep that the majority of this waste clearing takes place.