A team of neuroscientists from the University of Pennsylvania and Freiburg University who are using a video game in which people navigate through a virtual town delivering objects to specific locations, has discovered how brain cells that encode spatial information form geotags for specific memories and are activated immediately before those memories are recalled. Their work shows how spatial information is incorporated into memories and why remembering an experience can 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 Penn’s School of Arts and Sciences.
The study was led by Kahana and professor Andreas Schulze-Bonhage of Freiberg. Jonathan F. Miller, Alec Solway, Max Merkow and Sean M. Polyn, all members of Kahana’s lab, and Markus Neufang, Armin Brandt, Michael Trippel, Irina Mader and Stefan Hefft, all members of Schulze-Bonhage’s lab, contributed to the study. They also collaborated with Drexel University’s Joshua Jacobs.
Researchers have been conducting research with epilepsy patients who have electrodes implanted in their brains as part of their treatment. These electrodes capture electrical activity from throughout the brain while the patients participate in experiments. As with earlier spatial memory experiments conducted by Kahana’s group, this study involved playing a simple video game on a bedside computer. The game charged players with making deliveries to stores in a virtual city. Participants were given a period of free time to explore the city in the game 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 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).
“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.”
By asking participants to recall the items instead of the stores, researchers say that it made it easier to test if their spatial memory systems were being activated even when episodic memories were being accessed.
“During navigation, neurons in the hippocampus and neighboring regions can often represent the patient’s virtual location within the town, kind of like a brain GPS device,” Kahana said. “These so-called ‘place cells’ are perhaps the most striking example of a neuron that encodes an abstract cognitive representation.”
The results of the study were published in the journal Science. The research was supported by the U.S. National Institutes of Health, the German Research Foundation and Germany’s Federal Ministry of Education and Research.
You can learn more about the particulars of this fascinating research here.