A good night’s sleep restores memory Health and wellness

Everyone has a bad night now and then. Moving on to problems or worries at the end of the day hurts rest and especially deep sleep. As Charlotte Brontë wrote, “a restless mind is like a restless pillow.” A quality night’s sleep has a restorative effect. In addition, it is a recognized fact that sleep serves as a stimulus for learning and memory. More recently, some scientists have discovered that the first stage of deep, slow-wave sleep is extremely important.

“If you learn something in the evening, the learned information is reactivated during sleep,” says Björn Rasch, a professor at the University of Freiburg and a participant in the Horizon-funded MemoSleep project. The Swiss researcher adds that “negative thoughts increase sleep interruptions, make us wake up earlier than we want and make our sleep less deep”.

reactivation of thoughts

Not all news is bad, though. According to Rush, who conducted an experiment on this idea, positive thoughts can also reactivate circuits in the brain and improve sleep in the process.

His experiment thrilled the students at his university who took part in the project, who were paid 50 Swiss francs (€52) for each night they slept comfortably in a sleep lab equipped with four beds. The students were connected to an EEG that tracked their brain waves. Their muscles were also monitored to identify when they fell asleep and what state of sleep they were in.

According to him, some relaxation strategies help people sleep better, but do not affect the quality of subsequent sleep. In the test, the researcher had them listen to several hypnotic induction audio recordings that narrated, for example, the movements of a fish swimming in the deep sea, and included words suggesting safety and relaxation.

“Subjects spent more time in the deepest phase of slow-wave sleep after listening to hypnotic induction audio recordings. The explanation would be that during sleep there was greater reactivation of the relaxing and calming thoughts that were heard in the audio recordings,” he explains.

In future studies, Rush hopes to help insomnia patients. “Not only will it help them fall asleep, but they will also rest better while they sleep,” he points out. Similarly, this advance could help people with psychological illnesses, such as post-traumatic stress disorder, who have difficulty sleeping.

Seahorses and training

The seahorse-shaped part of the brain called the hippocampus (from the Greek word for seahorse) is vital when it comes to learning and memory. The scientific community often uses rodents to study the behavior of their hippocampus in learning and sleep.

Rats, for example, are particularly good at remembering the path to food in the middle of a maze. The hippocampus is a major component of this process.

Dr. Juan Ramírez-Villegas, a postdoctoral fellow at the Austrian Institute of Science and Technology, uses rodents to study how the mammalian brain stores memories, work that could help fight human diseases such as Alzheimer’s.

As part of the Horizon-funded DREAM project, Ramírez-Villegas discovered that another part of the brain, the brainstem, plays a key role in interacting with the hippocampus and is activated before it. “It seems that the brainstem forms a kind of decoration so that the hippocampus can reactivate memories in the different phases of sleep,” he says.

Using electrodes, Ramírez-Villegas recorded the brain activity of rats as they walked through a maze and later while they slept. Sleep allows the brain to replay everyday events and store them as long-term memories. “Impressively, the cells are activated during sleep in the same order as they were during learning, although they are more compressed in time during sleep,” he says.

The process of remembering

This finding is surprising because it suggests that the brainstem can stimulate and alter memory formation. This appears to be the case in both rodents and primates, and is therefore likely to be the primary brain mechanism in mammals, including humans.

This research, in addition to being essential for understanding the basic functioning of the brain, may also bring clinical benefits. “We are uncovering the basic principles of memory processes that can be used to mitigate the effects of diseases that affect memory,” adds Ramírez-Villegas.

The research described in this article was funded by the EU. Article originally published in HorizonJournal of European Union Research and Innovation.

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