The study explains how spatial information is incorporated into memories and why remembering an experience can quickly bring to mind other events that happened in the same place.

"These findings provide the first direct neural evidence for the idea that the human memory system tags memories with information about where and when they were formed and that the act of recall involves the reinstatement of these tags," said Michael Kahana, professor of psychology in University of  Pennsylvania's School of Arts and Sciences.

In the study, participants played a simple video game on a bedside computer. The game in this experiment involved making deliveries to stores in a virtual city.

The participants were given a period where they were could freely explore the city and learn the stores' locations.     When the game began, people were 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 13 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 the formation of spatial memories (the locations of the stores) and the recall of episodic memories (the list of items that had been delivered).

By asking participants to recall the items they delivered instead of the stores they visited, the researchers could test whether their spatial memory systems were being activated even when episodic memories were being accessed.

The map-like nature of the neurons associated with spatial memory made this comparison possible.

Using the brain recordings generated while the participants navigated the city, the researchers were able to develop a neural map that corresponded to the city's layout.

As participants passed by a particular store, the researchers correlated their spatial memory of that location with the pattern of place cell activation recorded.

With maps of place cell activations in hand, the researchers were able to cross-reference each participant's spatial memories as they accessed their episodic memories of the delivered items.

The researchers found that the neurons associated with a particular region of the map activated immediately before a participant named the item that was delivered to a store in that region.The study was published in the journal Science.


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