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U discovery gives insight into the brain’s 'replay' process

A. David Redish, Ph.D. A part of the brain essential for memory called the hippocampus has long been known to “replay” recently experienced events.

This replay previously was believed to be a simple process of reviewing recent experiences to help consolidate them into long-term memory.

But now Department of Neuroscience researcher A. David Redish, Ph.D., and colleagues have discovered that the replay function of the hippocampus is actually a much more complex cognitive process—a finding that could help investigators learn more about what happens in the brain when this decision-making process goes wrong.

By studying brain activity in rats, Redish and his colleagues found that it was not the most recent experiences that were played back in the hippocampus but instead the experiences they had encountered the least. The team also discovered that some of the replayed sequences were those they had never experienced, implying that the rat’s brain was able to make a mental map of the routes the rat hadn’t taken using routes it had taken as points of reference.

These observations, published in the March 11 issue of the journal Neuron, suggest that this hippocampal process plays an important role in an animal’s active learning process and may also play a role in maintaining the animal’s internal representation of the world, or its “cognitive map.”

“The point of the cognitive map is flexibility,” Redish says. “It gives animals the ability to plan novel paths within their environment. This replay process may be an animal’s way of learning how the world is interconnected so it can plan new routes or paths.”

Redish hopes this work can shed light on the poorly understood human decision-making process and, eventually, the causes of neurocognitive disorders.

“Before we can understand how this process goes wrong in people with diseases such as addiction or Alzheimer’s, we first need to understand how cognitive connections are made in the brain and how humans make decisions in relation to their internal, cognitive map,” he says. “Once we have an understanding of how things work in normal brain processing, we can understand where they can break. And then we can understand what we can do to try to fix them.”

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