November 29, 2013
Your Brain ‘Geotags’ Memories, Linking Them To Specific Places
Brett Smith for redOrbit.com - Your Universe Online
On Twitter, users can categorize their post by using a hashtag, which connects the tagged post to all other posts with the same identifier. A new study in the journal Science has found that our brains do something similar, by ‘geotagging’ our memories to a specific location.
Using experiments involving study participants navigating through a virtual town, the team of American and German scientists concluded that brain cells encode spatial information for specific memories and these brain cells are activated just before those memories are recalled.
"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 at the University of Pennsylvania.
For their study, the team enlisted epileptic patients who had electrodes placed into their brains as a part of their treatment regimen. The electrodes allowed researchers to record electrical activity from all over the brain while the patients participated in experiments from their hospital beds.
Study volunteers were asked to play a simple video game that involved delivering virtual packages to stores in a virtual city. They started by freely exploring the city and learning the locations of various stores. When the more active part of the game started, participants were instructed to deliver a package to a specific location, without being told what the package contained. After a successful delivery, the participant was told what item that had been delivered, and given their next delivery stop.
The game ended after 13 deliveries, after which participants were asked to remember and name as many of the items delivered as possible while their brain activity was being monitored. The researchers were then able to correlate patterns of neural activity to the formation of spatial memories of the stores and episodic memories of items that had been delivered.
"A challenge in studying memory in naturalistic settings is that we cannot create a realistic experience where the experimenter retains control over and can measure every aspect of what the participant does and sees. Virtual reality solves that problem," Kahana said. "Having these patients play our games allows us to record every action they take in the game and to measure the responses of neurons both during spatial navigation and then later during verbal recall."
Using the brain activity data, the researchers developed a neural map that correlated to the virtual city's layout. As participants moved by a particular store, the study team connected their spatial memory of that location to a specific pattern of brain cell activation.
"This means that if we were given just the place cell activations of a participant," Kahana said, "we could predict, with better than chance accuracy, the item he or she was recalling. And while we cannot distinguish whether these spatial memories are actually helping the participants access their episodic memories or are just coming along for the ride, we're seeing that this place cell activation plays a role in the memory retrieval processes."
With most of the activity in the study observed in the hippocampus, the new study supports previous research that identified the brain structure as a sort of cartographer as well as a recorder of events for episodic memory.
"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 said.