“There has to be some sort of segregation to remember what’s important and forget the rest,” Zugaro said. “Understanding how specific memories were selected for storage was still lacking… Now we have a good lead.”
Last December, a research team led by Bendor of University College London published similar results in the journal Nature Communications, which predicted Yang and Buzsáki’s results. They also found that the piercing waves that shot when the rats were awake and sleeping seemed to imply experiences for memory. But their analysis averaged a range of different trials together—a less precise approach than what Yang and Buzsáki achieved.
The NYU team’s key innovation was introducing a time element into the analysis that distinguishes similar memories from each other. Mice ran the same maze patterns, yet the researchers were able to distinguish blocks of trials at a neural level—a feat never achieved before.
Brain patterns mean “something a little closer to the event and a little less like general knowledge,” he said. Loren Frankneurobiologist at UC San Francisco who was not involved in the study. “That strikes me as a really interesting finding.”
“They show that the brain may create some kind of temporal code to distinguish between different memories that occur in the same place,” he said. Freyja Olafsdottira neurobiologist at Radboud University who was not involved in this research.
Shantanu Jadhavneurobiologist at Brandeis University, praised the study. “It’s a good start,” he said. But he hopes to see a follow-up experiment that includes a behavioral test. Showing that an animal forgot or remembered specific trial blocks would be “real proof that this is a marking mechanism.”
The research leaves a burning question unanswered: Why is one experience chosen over another? The recent work suggests how the brain tags an experience to remember it. But it can’t tell us how the brain decides what’s worth remembering.
Sometimes the things we remember seem random or irrelevant, and certainly different from what we would have chosen if we had the choice. “There’s a sense that the brain prioritizes based on ‘importance,’” Frank said. Because research suggests that emotional or novel experiences tend to be remembered better, it’s possible that internal fluctuations in arousal or levels of neuromodulators such as dopamine, adrenaline and other chemicals that affect neurons ultimately determine the choice of experiences, he suggested.
Jadhav echoed that idea, saying, “The internal state of the organism may cause experiences to be encoded and stored more efficiently.” But it’s not clear what makes one experience more likely to be stored than another, he added. And in the case of Yang and Buzsaki’s study, it’s not clear why a mouse would remember one trial better than another.
Buzsáki remains committed to studying the role piercing waves play in the hippocampus, though he and his team are also interested in the potential applications that might arise from these observations. It’s possible, for example, that scientists could disrupt the waves as part of a treatment for conditions like post-traumatic stress disorder, in which people remember certain experiences too vividly, he said. “The low-hanging fruit here is erasing the sharp waves and forgetting what you’ve experienced.”
In the meantime, Buzsáki plans to continue studying these powerful brain waves to learn more about why we remember what we do.
Original story reprinted with permission Quanta Magazineeditorially independent publication Simons Foundation whose mission is to advance public scientific knowledge by reporting on scientific achievements and trends in mathematics, physics and biological sciences.