(CNN) New York researchers created a virtual reality maze for rats in an attempt to demystify a question that has plagued neuroscientists for decades: How are long-term memories stored?
What they found surprised them. After forming in the hippocampus, a curved structure deep in the brain, the mice’s memories were actually rooted in what’s called the anterior thalamus, an area of ​​the brain that scientists don’t typically associate with memory processing at all.
“It was very interesting and unexpected for us that the thalamus was a clear winner here,” said Priya Rajasethupathi, associate professor at Rockefeller University and one of the authors of a peer-reviewed study published in the journal. cell This week. The thalamus “is often thought of as a sensory relay, not very cognitive, not very important in memory.”
But this new research suggests that it may play an important role in converting short-term memory into long-term memory. And Rajasethupathi said the thalamus should make it a key area of ​​study for researchers trying to help patients suffering from conditions like Alzheimer’s, who are able to remember old memories but may have trouble remembering new information.
“It engages a part of the brain — the thalamus — with long-term storage of memories that no one else has anticipated,” said Lauren Frank, a professor of physiology at the University of California, San Francisco. who were not involved in the study.
Inside the study
Rajasethupathy noted that neuroscientists have long known that memories are formed in the hippocampus, and that it is the focus of much research surrounding conditions such as amnesia and Alzheimer’s.
Past research “has led to this model where memories are formed in the hippocampus but become independent over time and gradually stabilize in the cortex,” the wrinkled, outer part of the brain. The question is exactly how memories travel from one region to another, says Rajasethupathi.
“That process was mysterious, I would say, for over 50 years,” Rajasethupathi said.
The time was right for his lab to try to identify an answer, he added, thanks to new technology that allowed researchers to track activity in multiple parts of each subject’s brain. The inventions enabled the team to trace how memories travel when rats learn to navigate a maze.
“I think what they did was technically very challenging,” Frank said. “Especially where they were trying to (observe) activity from multiple neurons in three different regions simultaneously using this type of fiber microscope. It’s a pretty state of the art thing.”
The research — led by Rockefeller graduate students Andrew Toder and Josue Regalado, working in Rajasethupathi’s lab — involved strapping rats into a headpiece designed to hold them still while a machine used optical fibers to record their brain activity.
The maze led them to different “chambers” that provided either stimuli, such as sugar water, or aversives, such as mouth air.
The rats returned to the maze for a few days, enough time to form long-term memories.
“The analogy would be your birthday dinner versus the dinner you had three Tuesdays ago,” Toder said in a statement. “You’re more likely to remember what you had on your birthday because it’s more rewarding for you — all your friends are there, it’s exciting — versus just a simple dinner, which you might remember the next day but maybe not a month later.”
Meanwhile, the researchers used chemicals to block parts of the mice’s brains to see how it affected their ability to create and store memories.
Not only did they find that the anterior thalamus was an important pathway for these memories – they also found that by stimulating that part of the mice’s brain, the researchers “were able to help the mice retain memories that they would normally forget”. A news release About the study
Rajasethupathi added, “Some memories are more important to us than others. We found that not only do rats need the anterior thalamus to consolidate memories, but by activating it, we can increase the consolidation of a memory that rats normally forget.”
What does this mean?
Rajasethupathi noted that the study had some limitations. For example, this does not indicate that traveling through the anterior thalamus is the only route that memories can take to long-term storage.
“I want to be “Make it clear that this is not the end,” he said. “Maybe not everything comes together this way. But I’m very confident it’s a very important circuit.”
This research also relies on mice, which do not have the same brain as humans but have proven to be extremely useful models for discovering how our own brains work. The long-term memory storage process takes weeks in mice, while it can take months for humans, Rajasethupathi added.
It’s also possible that different types of memories take different highways, he noted. There are explicit memories, which focus on facts, figures, and specific data points, and implicit memories are usually tied to emotions and can be formed without a person realizing it. The thalamus may not be equally involved for both types of information.
But Frank, the UCSF professor, said the study will have broader implications for future research, encouraging further investigation into the thalamus’ role in memory storage.
“It’s nice to get the field to a point where we can think about the long-term evolution of memory and try to understand how it works,” he said. “And the study is certainly a step in that direction.”
