Memory: How the brain decides what we remember

Whether it's studying for a test, finding your way in a new environment, or getting to know people you didn't know before: after people encounter something, neurons in their brain produce Hippocampus Several different signals.

These include sharp signal waves known in English as “sharp wave ripples”, which arise when the electrostatic charge in brain cells changes. “Every experience has its own unique waveform,” the neuroscientist explains Gyorgy Buzacki from NYU Grossman School of Medicine told science.ORF.at.

Remember or forget?

It is already known from previous studies that “sharp waves” affect the information that is transferred to long-term memory. “What was not known until now is how this works in detail and, above all, how the brain decides whether we should remember an experience for a long time or whether we can forget it again soon,” explains Buzsaki.

In collaboration with a research team led by doctoral student Wan'an Yang of NYU Grossman School of Medicine, the neuroscientist investigated the mechanisms behind long-term memory formation. The resulting Stady The researchers are currently presenting it in the journal Science.

The brain needs rest periods

According to the neuroscientist, what is particularly important for memory is that the brain does not absorb information continuously. “There are different stages – the stage where impressions and information are collected, and then there are also short periods of rest.” During these periods, which usually last only a few milliseconds, the brain pauses for a moment to process what it has experienced. In these sections, neurons also produce sharp signal waves.

The fact that the brain relies on several periods of rest is also evident in everyday life. They're the reason why your thoughts keep wandering when reading complex texts. If you want to learn something and remember it for a long time, it is important to take breaks every now and then to give your brain cells enough time to process the new information.

The amount of signal is crucial

As part of the study, the researchers showed that it is the amount of sharp signal waves that determines which information goes into long-term memory and which does not. “The more neurons produce these items immediately after the experience, the more likely they are to remember them later,” says Buzsaki.

This is mainly because the signal waves generated during the day are later repeated subconsciously thousands of times during sleep. If there are more signal waves following an experience from the beginning, this automatically leads to more repetition during sleep and ultimately to a more effective imprint in long-term memory.

The team came to this conclusion with the help of mice: the animals had to run through mazes while the researchers recorded signals in the mice's brains. If at least five to twenty sharp signal waves appeared in the animals' hippocampus after the experiment, they remembered the different branches of the target better. However, the rats quickly forgot the information that fewer or no signal waves were measured.

Reward strengthens memories

The number of sharp signal waves that arise after the experiment can also be affected. The experiment on mice showed that their neurons produced more “spike spikes” when the animals were rewarded with sugar after the maze. “Reward plays an important role in memory,” Buzsaki says. According to the neuroscientist, this is probably because the mouse wants to get a reward in the future and is unconsciously saving the experience so that it can get sugar again later.

It's similar with people. However, the form of reward varies greatly from person to person and depends on the situation. The prospect of doing well on a test the next day can also be a reward for some people. “Different people care about different things,” Buzsaki said.

Strengthening memory and erasing memories

Knowing the mechanisms behind long-term memory formation is important for several reasons. On the one hand, according to Buzsaki, this is another step towards a better overall understanding of the human brain and therefore also the causes of diseases such as Alzheimer's.

After further research in this area, it may at some point be possible to artificially improve people's memory, or, conversely, delete particularly traumatic memories from their memory, with the help of “sharp waves”.