How the brain decides what to remember

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“There must be some kind of triage to remember what is relevant and forget the rest,” Zugaro said. “It was still difficult to understand how specific memories were selected for storage … now we have a good clue.”

Last December, a research team led by Bendor at University College London published related results in Nature Communications, which preceded Yang and Buzsaki’s results. They too found that sharp waves emitted during rats’ waking and sleeping periods appeared to tag experiences for memory. However, their analysis averaged many different trials – which was less accurate than the work done by Yang and Buzsaki.

The NYU team’s main innovation was to bring the element of time, which separates similar memories from one another, into their analysis. The rats were running around in the same maze pattern, and yet these researchers could distinguish between blocks of trials at the neuronal level — a solution that had never been reached before.

The brain patterns are marking “something a little closer to an event and a little less than common sense,” said Lauren Frank, a neuroscientist at UC San Francisco who was not involved in the research. “That strikes me as a really interesting finding.”

“They’re showing that the brain is probably creating some kind of temporal code to distinguish between different memories that occur in the same place,” said neuroscientist Freya Olafsdottir of Radboud University, who was not involved with the work.

Brandeis University neuroscientist Shantanu Jadhav praised the study. “It’s a good start,” he said. However, he hopes to see a follow-up experiment that includes a behavioral test. Demonstrating that an animal forgot or remembered a particular test block “would be real evidence that this is a tagging mechanism.”

The research has left a burning question unanswered: Why is one experience chosen over another? The new research explains how the brain tags a particular experience for memory. But it cannot tell us how the brain decides what is worth remembering.

Sometimes the things we remember seem random or irrelevant, and they certainly differ from what we choose to remember. “It seems that the brain prioritizes based on ‘importance,'” Frank said. Because studies have suggested that emotional or new experiences are better remembered, it’s possible that internal fluctuations in arousal or the levels of neuromodulators such as dopamine or adrenaline and other chemicals that affect neurons drive the selection of experiences, he suggested.

Jadhav reiterated this idea, saying, “The internal state of the organism may bias it to encode and store experiences more effectively.” But it’s not known what makes one experience more prone to be stored than others, he said. And in the case of Yang and Buzsáki’s study, it’s not clear why a rat would remember one trial better than another.

Buzsáki is committed to exploring the role of sharp wave ripples in the hippocampus, although he and his team are also interested in potential applications arising from these observations. For example, it’s possible that scientists could disrupt the waves as part of treatment for conditions such as post-traumatic stress disorder, in which people remember certain experiences very vividly, he said. “The easiest way here is to erase the sharp waves and forget what you experienced.”

But for now, Buzsáki will continue to focus on these powerful brain waves, to figure out why we remember the things we do.


The original story is republished with permission from Quanta Magazine, an editorially independent publication. Simons Foundation Whose mission is to enhance the public’s understanding of science by covering research developments and trends in mathematics and the physical and life sciences.

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