Matt Wilson studies memories replayed in the brain

MIT professor Matt Wilson studies rats’ brains to learn about the process of human memory. He’s interested in a brain structure called the hippocampus, which, Wilson said, functions in a very similar way in rats and humans.

Matt Wilson: This is a structure we know is critical for forming and retrieving memory in both rodents and in humans.

In Wilson’s experiments, he implants very fine electrode wires – wires thinner than a human hair – into rats’ brains, near groups of brain cells, in order to watch and listen to activity in the memory center of the brain

Matt Wilson: The idea is that memories ultimately are expressed in the brain as patterns of activities across these neurons. We can tune in our audio monitors to the electrical activity. They sound like “cch!” That’s it, “cch!”

Wilson found that while rats were in repose, their brains were actively recalling previous experiences. Wilson said memories seem to be composed of short segments, compressed and replayed in fractions of seconds.

Matt Wilson: Our past and recent experiments looking at these phenomena we call ‘memory replay events’ tell us that the hippocampus continues to work on memory. So the question becomes, what is it working on?

Wilson said that understanding how these memory patterns are connected to other types of thought could help us better understand human intelligence and solve diseases of memory like Alzheimer’s.

Wilson’s lab records the patterns that these brain cells make, for weeks at a time.

Matt Wilson: We can see these recordings as they’re formed and then we can see when patterns reappear, when those memories are retrieved or processed by the brain.

As he examined the structure of these retrieved, or reactivated memories, Wilson found that when the animals were sitting quietly, or thinking, the memories were compressed in time.

Matt Wilson: They’re short fragments, each lasting a fraction of a second, connected together. They’re like links in a chain. Each link is like a small brief episode that corresponds to just a few seconds of the animal’s actual experience. So memories seem to be composed of small fragments – or chunks – that are connected together, compressed in time, and then replayed during sleep, or quiet thought.

Wilson said this memory replay phenomenon shows us that the hippocampus is always working on memory, on a subconscious level. In other words, memories are more complex than we previously thought.

Matt Wilson: It challenges us to think about how memory is not just formed, but how it ultimately is used to contribute to something else. What is that something else? We think of memory as a part a process of what we refer to as cognition, intelligence, or how we build models of the world to help guide our actions.

Wilson is optimistic that in the future, we will have a complete understanding about how the brain works.

Matt Wilson: What’s most striking about research to this point is we have been able to gain insights to structure of memory. Not because we’re so clever, it’s because the brain is not doing something so complicated that we can’t understand it. When we look at these patterns, we can see patterns how they unfold. It’s accessible. It tells us that it’s understandable, and we’re likely to figure out mechanisms that control this.

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