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BY ANTHONY KING

Everyone suffers from restless nights from time to time. Chewing on failures or worries at the end of the day undermines rest, especially deep sleep. “A disheveled mind makes a restless pillow,” wrote author Charlotte Brontë.

A good night’s sleep serves as a tonic. Moreover, it has long been recognized that closing the eyes stimulates learning and memory. More recently, scientists have revealed that the early phase of slow-wave deep sleep is particularly important.

“When you learn something in the evening, that information is reactivated during sleep,” said Dr Bjoern Rasch, who participated in the Horizon-funded MemoSleep project and is a professor at the University of Fribourg.

The Swiss researcher added that “ruminations and negative thoughts increase our awakenings during sleep, make us wake up earlier than we want and cause us to sleep less soundly”.

Reactivated Thoughts

But there is also good news. Positive thoughts can also be reactivated in brain circuitry and, in doing so, improve sleep, according to Dr. Rasch. He organized an experiment around the idea.

His test was a small boon to students at his university who received 50 Swiss francs (52 euros) for each night spent dozing in a comfortable four-bed sleep lab.

The students were hooked up to an electroencephalogram that monitored their brain waves. They also had their muscles monitored to record when they fell asleep and what state of sleep they were in.

Some relaxation strategies help people fall asleep faster, but don’t change the quality of sleep afterwards, according to Dr. Rasch. He played hypnotic tapes with images such as a fish swimming in deep water, and with words suggesting safety and relaxation, for the students.

“The subjects spent more time in the slow-wave deep sleep phase after listening to the hypnotic tape,” Dr. Rasch said. “This would be explained by an increased reactivation of relaxing and reassuring thoughts during sleep, previously heard during the hypnosis tape.”

In future studies, Dr. Rasch hopes to help patients who suffer from insomnia.

“It could not only help them fall asleep, but also make their sleep more restful,” he said. Additionally, it could help people with psychological illnesses, such as post-traumatic stress disorder, who sleep poorly.

Seahorses and learning

The seahorse-shaped part of the brain called the hippocampus (from the Greek word for hippocampus) is particularly important for learning and memory. Scientists often use rodents to study their hippocampus in learning and sleep.

Rats, for example, are masters at remembering paths through labyrinths to find food. The hippocampus is the key to this recall.

Dr. Juan Ramirez-Villegas is using rodents to probe how the mammalian brain stores memories – work that could eventually help fight human diseases such as Alzheimer’s.

As part of the Horizon-funded DREAM project, he discovered that another part of the brain – the brainstem – plays a crucial role along with the hippocampus and becomes active upstream.

“It seems that the brainstem sets the stage for the hippocampus to reactivate memories at different stages of sleep,” said Dr. Ramirez-Villegas, postdoctoral researcher at the Austrian Institute of Science and Technology.

He attached electrodes to record activity in the brains of rats as they navigate a maze and then while they sleep. Sleeping allows the brain to replay the events of the day and engrave them as long-term memories.

“It’s very striking that the cells fire in the same order during sleep as during learning, but they are more compressed in time during sleep,” said Dr Ramirez-Villegas.

how we remember

The finding was surprising because it suggests the brainstem has an overlooked function in stimulating and modifying memory formation. This appears to be true for rodents as well as primates, and therefore is likely to be a basic brain mechanism of mammals, including humans.

The research, while crucial to understanding basic brain functioning, could also have clinical benefits. “We are unraveling the basic principles of memory processes, but we can also use them to improve the effects of memory-related diseases,” said Dr. Ramirez-Villegas.

The research in this article was funded by the European Research Council of the EU and the Marie Skłodowska-Curie Actions (MSCA). This article was originally published in Horizonthe European magazine for research and innovation.

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