A good night’s sleep is a restorative for memory | Health & Wellness

Everyone has a bad night from time to time. Going over problems or worries at the end of the day harms rest and especially deep sleep. As Charlotte Brontë wrote, “a restless mind is like a restless pillow”. A good quality night’s sleep acts as a restorative. Moreover, 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 Bjoern 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 cause our sleep to be less deep.”

reactivation of thoughts

However, it is not all bad news. According to Rasch, who has organized an experiment on this idea, positive thoughts can also reactivate circuits in the brain and improve sleep in the process.

His experiment excited the students at his university who took part in the project, who received 50 Swiss francs (52 euros) for each night they slept comfortably in a sleep laboratory equipped with four beds. The students were hooked up to an electroencephalogram that tracked their brain waves. Their muscles were also observed to identify when they fell asleep and what sleep state they were in.

In his opinion, some relaxation strategies help people fall asleep better, but do not influence the quality of subsequent sleep. In the test, the researcher made them listen to several hypnotic induction audios that narrated, for example, the movement of a fish swimming in the depths of the sea, and included words suggestive of safety and relaxation.

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

In future studies, Rasch hopes to help patients with insomnia. “It would not only help them fall asleep, but also help them have a better rest while they sleep,” he says. Similarly, this advance could help people with psychological illnesses, such as post-traumatic stress disorder, who have difficulty sleeping.

Seahorses and learning

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

Rats, for example, are especially 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 postdoctoral fellow at the Austrian Institute of Science and Technology, uses rodents to explore how the mammalian brain stores memories, work that could help fight human diseases such as Alzheimer’s.

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

By means of electrodes, Ramírez-Villegas has recorded the brain activity of rats while they went through a maze and, later, while they slept. Sleep allows the brain to replay daily events and store them as long-term memories. “It’s impressive that cells fire during sleep in the same order as they did during learning, even though they are more compressed in time during sleep,” she says.

The process of remembering

This discovery has been amazing because it suggests that the brainstem can stimulate and modify memory formation. This appears to be the case in both rodents and primates, and thus is likely to be the basic brain mechanism of mammals, including humans.

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

The research described in this article has been financed with EU funds. Article originally published in Horizonthe Journal of Research and Innovation of the European Union.

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