How the brain decides which memories are important and should be remembered and which ones it can forget and let get lost.

Memory can be a mystery. Certain events in our lives remain clear in our brain no matter how much time has passed, while episodes from the previous day may already be blurry and difficult to remember.

A study, published Thursday in the journal Science, sheds light on why this happens: scientists have discovered that the brains of humans and other mammals have a system for choosing which life experiences are important enough to be recorded in memory. long term and which ones are not.

Experiments with mice have revealed that, during waking hours, cells in the hippocampus of the brain activate in a specific pattern called “sharp wave ripples”which marks important experiences and then transfers them to long-term memory during sleep.

Although the research was carried out in mice, certain brain processes have remained practically unchanged throughout the evolution of mammals, so the findings may provide clues about our experience, said the study's lead author, Dr. György Buzsáki. , Biggs Professor of Neuroscience at New York University – Langone Health.

As part of the research, Buzsáki and his colleagues put mice through a maze that had a sugary reward at the end for those who made it there. Meanwhile, the researchers monitored the activity of nerve cells using electrodes implanted in the rodents' brains that sent data to computer programs.

They observed that when the mice paused to eat, their brains produced sharp waves that repeated up to 20 times. The diurnal pattern of sharp waves occurred again during the night, a process that transferred the experience to long-term memory.

It is during sleep that the experiences of waking hours are considered important. They become lasting memories.

The researchers observed that events that were followed by very few, if any, sharp waves ended up being lasting memories.

According to Buzsáki, this process of labeling memories during waking hours is completely unconscious. “The brain decides on its own instead of us doing it voluntarily,” he explained.

Relaxation is necessary for long-term memory functioning, the study adds, which further suggests that there are other things we can do to increase the likelihood that a memory will be stored permanently.

According to Buzsáki, if, like mice, we pause after an experience, the events may become recorded in long-term memory. We need that period of relaxation, in which we do not pay much attention to anything, so that the acute waves are activated. This waking process is essential to create a permanent memory.

In practice, this means that if you like to watch TV series for several hours, you probably won't remember much of any episode except the last one you watched, Buzsáki explained.

“If you see a movie and want to remember it, it's better to go for a walk afterwards,” said Buzsáki, “no double sessions.”

According to Daniela Schiller, professor of Neuroscience and Psychiatry at the Icahn School of Medicine at Mount Sinai, one of the most intriguing findings of the research is the discovery that bursts of activity – in this case, sharp waves – can occur when the mouse is still and its brain is practically stopped.

What was surprising, according to Schiller, is that the pattern of brain activity recorded near the event was the same as that observed during sleep. Both imitated the experience of the real mouse experience.

The study showed that events followed by a pause and electrical bursts in the brain are what we will find in long-term memory, explained Daphna Shohamy, director of the Zuckerman Institute at Columbia University. If you watch animals, you can see them pause during the day after a novel or rewarding experience, she explained.

“A few years ago we did a study where we had people go through a maze with random objects in search of treasure,” Shohamy said: “If they got the treasure, they were more likely to remember the random object they had seen along the way.” .