The hippocampus in the brain is associated with remembering events and tracking locations. Until recently, researchers had been unable to determine whether the same sets of neurons were involved in both of these processes.
Now, because of a video game-based experiment, a team from Penn, Freiburg University, and Drexel has shown that these systems work together, adding a spatial “geotag” to memories of specific events.
The study was led by Michael Kahana, a professor in the Department of Psychology in the School of Arts & Sciences. His body of research has produced insights into the way memory works on the level of individual neurons, including specialized neurons called “place cells,” which help people keep track of spatial information.
Like many of his earlier experiments, Kahana’s new study involved a video game played by epilepsy patients who had electrodes implanted in their brains as part of their treatment. These electrodes allowed Kahana and his colleagues to directly measure the activation of the participants’ neurons, both while they played and when they were asked to recall things that happened during the game.
The game in this experiment involved making deliveries to stores in a virtual city. The participants were first given a chance to freely explore the city and learn the stores’ locations. When the game began, participants were only instructed where their next stop was, without being told what they were delivering. After they reached their destination, the game would reveal the item that had been delivered, and then give the participant their next stop.
After 12 deliveries, the screen went blank and participants were asked to remember and name as many of the items they had delivered in the order they came to mind. This allowed the researchers to correlate the neural activation associated with memories of places (the locations of the stores) and the recall of memories of events (the list of items that had been delivered).
“What we show is that the moments leading up to recall of a item involve a reactivation of the cells that fired when you were driving by the associated store,” Kahana says. “This means that if we were given just the place cell activations of a participant, we could predict, with better than chance accuracy, the item he or she was recalling.”
Earlier neuroscience research in both human and animal cognition had suggested the part of the brain where these neurons reside, the hippocampus, has two distinct roles: the role of cartographer, tracking location information for spatial memory, and the role of scribe, recording events for episodic memory. This experiment provides further evidence that these roles are intertwined.
“Our finding that spontaneous recall of a memory activates its neural geotag suggests that spatial and episodic memory functions of the hippocampus are intimately related and may reflect a common functional architecture,” Kahana says.