Sleep used to be regarded as a time when the brain turned itself off to recharge its batteries, but research over the past 20 years has put that theory to rest.

Functional magnetic resonance imaging (fMRI) scanners, which use magnetic resonance to generate images of brain activity, have shown that the organ is active during sleep.

Although there is still much to be discovered, the brain uses that time to clean out toxins and repair itself, and to reinforce memories and lessons learned during the day.

Sleep research is a relatively new discipline, but it’s already understood that a good night’s sleep is much more important to our overall health and well-being than was previously thought.

Sleep is set to become the next health revolution, similar to the way diet revolutionised our view of healthy living in the 20th century.

Sleep research has also opened up a new avenue of scientific inquiry – “sleep engineering”. As our understanding of what happens when we sleep improves, scientists are developing ways to influence our sleep so that its benefits are maximised.

In a presentation for New Scientist Events, a webinar organised by the British science weekly New Scientist, Penelope Lewis, professor of neuroscience at Cardiff University in Wales, discussed current trends in the field. Lewis’ research involves experiments which manipulate sleeping subjects’ brainwaves to boost memory, and guard against age-related problems like dementia.

The experiments revolve around a technique called electroencephalography (EEG), in which electrodes placed on the scalp measure the brain’s electrical activity during sleep – neurons, the cells that the brain uses to communicate with itself, work by firing off electrical impulses. The resulting measurement depicts oscillations, which look like soundwaves.

When they have mapped a subject’s brainwave activity, Lewis and her team focus on certain patterns in the oscillations and try to artificially manipulate them, to trick the brain into doing things that benefit the sleeper.

The three phases of sleep are light sleep, slow wave sleep – commonly known as deep sleep – and rapid eye movement (REM) sleep. Each phase produces different oscillations, as the brain is carrying out different functions.

Repairing damage during sleep

Researchers have not fully figured out the brain’s actions, but believe that it’s engaging in restoration and repair, and consolidating learning and memory.

The brain flushes out beta amyloids, for instance, toxins that can cause the plaques that have been associated with age-related damage like dementia. It clears them out twice as quickly during sleep.

As we age, our sleep becomes disrupted, says Lewis. The oscillations during slow wave sleep are stretched out – the waves look flatter. The extent of this stretching mirrors the deterioration in our brain. This is where sleep engineering comes in, she says. If the stretching can be reversed, perhaps the deterioration in the brain will slow as a result.

Lewis says that a new technique called “closed-loop auditory stimulation” has managed to achieve this, and has boosted memory in sleeping patients. It is something she hopes will ultimately be able to combat memory loss resulting from dementia.

“We make simple sounds at exactly the right times during the oscillations to boost the amplitude [volume] of the cell waves. We are hoping this may help us ameliorate some of the loss of cell oscillation and potentially slow down some of the age-related damage,” she says.

“We monitor the EEG online, and detect when an oscillation is coming to a peak. At that time, we produce a clicking sound, and the click will boost the amplitude of the oscillation. That also boosts the next peak, and a little bit after that. If we keep applying these clicks through the night, we can boost the amplitude of slow wave sleep,” says Lewis.

This technique works well on young people, and has been shown to improve their memory during a night of sleep – their memory functions much better the day after stimulation, Lewis says. So far, it has not worked as well in older people.

Consolidating the day’s learning

As anyone who has taken the popular online Coursera course Learning How to Learn will know, learning is consolidated by a good night’s sleep. If you have an exam the next day, it’s better to go to bed early than stay up cramming.

“Individuals are significantly better at tests the next day after sleep,” Lewis notes. “There is a dramatic overnight improvement, and a real improvement the next day to the next evening.”

The learning consolidation – a function of memory – occurs with all types of sleep and is related to the number of peaks in the oscillations in the EEG.

“The brain practises recently learned memories – it is essentially rehearsing during sleep. There is a reactivation of memory during sleep, and that reactivation is important for the consolidation of memories. People improve overnight.”

“Sleep engineering comes in a very interesting way,” says Lewis. “It turns out that we can control the memory in the brain with a technique called ‘targeted memory reactivation’. Recently acquired memories are paired with a sound, and then the sound is played during sleep. That triggers the memory reactivation process and develops a consolidation,” says Lewis.

The reactivated memory is stronger for 10 days, although it will fade after 20 days.

“But there are also structural changes in the brain – an increase in grey matter after about 10 days,” Lewis says. “So a little bit of cueing in the night leads to long-term functional, structural, and behavioural changes in the brain. It’s quite amazing.”

South China Morning Post