A good night’s sleep restores memory

Everyone has a bad night from time to time. Dealing with problems and worries at the end of the day is detrimental to rest and especially deep sleep. As Charlotte Brontë wrote, “A restless mind is like a restless pillow.” A good night’s sleep acts as a restorative agent. Moreover, it is an accepted fact that sleep serves as a stimulus for learning and remembering. Recently, some scientists have found that the first stage of deep, slow 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 our sleep becomes less deep.”

reactivation of thoughts

However, it’s not all bad news. According to Rush, who conducted an experiment on this idea, positive thoughts can also reset brain circuits and improve sleep.

His experience has inspired students at his university who participated in the project, who were paid 50 Swiss francs (€52) for each night they slept soundly in a four-bed sleep lab. The students were connected to an electroencephalogram that tracked their brain waves. Their muscles were also monitored to determine when they fell asleep and what state they were in.

In his view, some relaxation strategies help people sleep better but do not affect subsequent sleep quality. During the test, the researcher had them listen to several hypnotic induction recordings that described, for example, the movement of a fish swimming in the deep sea and included words suggesting safety and calmness.

“Subjects spent more time in the deepest slow-wave sleep stage while listening to the hypnotic induction audios. The explanation would be that during sleep there was a greater activation of the soothing and calming thoughts that were heard in the audios,” he explains.

In further research, Rush hopes to help insomniacs. “It will not only help them fall asleep, but also help them rest better while sleeping,” he says. Likewise, this advance could help people with psychological illnesses, such as post-traumatic stress disorder, who have trouble sleeping.

Seahorses and training

A seahorse part of the brain called the hippocampus (from the Greek word for seahorse) is vitally important in learning and memory. The scientific community often uses rodents to study the behavior of their hippocampus during learning and sleep.

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

Dr. Juan Ramírez-Villegas, a PhD student at the Austrian Institute of Science and Technology, uses rodents to study how the mammalian brain stores memories, which 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 during different stages 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 daily events and store them as long-term memory. “Impressively, cells are activated in the same sequence during sleep as they are during learning, even though they are more compressed in time during sleep,” he says.

The process of remembering

This finding was surprising because it suggests that the brainstem can stimulate and modify memory formation. This appears to be the case in both rodents and primates, and is therefore likely to be a key mechanism in the mammalian brain, including humans.

In addition to being important for understanding basic brain activity, this research may also have clinical benefits. “We are uncovering 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. The article was originally published HorizonJournal of Research and Innovation of the European Union.

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