Memories are 'geotagged' with spatial information, study finds

November 28, 2013
Using a video game in which people navigate through a virtual town delivering objects to specific locations, a team of neuroscientists from the University of Pennsylvania and Freiburg University 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 quickly bring to mind other events that happened in the same place. This still image was taken from one of a German participant's delivery runs. Video files of gameplay are available upon request. Credit: University of Pennsylvania

Using a video game in which people navigate through a virtual town delivering objects to specific locations, a team of neuroscientists from the University of Pennsylvania and Freiburg University 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 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 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.

Their study was published in the journal Science.

The video will load shortly
This video demonstrates a sample trial, or "delivery day," of the virtual navigation memory task described in the manuscript. First, the participant will travel to twelve of the stores in the virtual town, and, at each store, the participant will be told the name of a common item. The participant will then travel to a thirteenth store, and upon arrival, the screen will turn black and a tone will sound. During the following 90 seconds, the participant will attempt to recall as many of the twelve delivered items as possible, in any order in which they come to mind. Translated English text (white text in parentheses) was added to the video and not present during the trial. Credit: University of Pennsylvania

Kahana and his colleagues have long conducted research with epilepsy patients who have electrodes implanted in their brains as part of their treatment. The electrodes directly capture electrical activity from throughout the brain while the patients participate in experiments from their hospital beds.

As with earlier spatial memory experiments conducted by Kahana's group, this study involved playing a simple on a bedside computer. The game in this experiment involved making deliveries to stores in a virtual city. The participants were first given a period where they were allowed 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 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 (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."

Using a video game in which people navigate through a virtual town delivering objects to specific locations, a team of neuroscientists from the University of Pennsylvania and Freiburg University 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 quickly bring to mind other events that happened in the same place. This overhead map of the virtual city is overlaid with the areas where a participants place cells were activated. Different colors represent different cells, showing how these neurons help track spatial information and memories. Credit: University of Pennsylvania

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.

"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."

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. To avoid confounding the episodic memories of the items delivered with the spatial memory of a store's location, the researchers excluded trips that were directly to or from that store when placing it on the neural map.

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.

"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."

Earlier neuroscience research in both human and animal cognition had suggested 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 said.

Explore further: Modifying activity of neuronal networks that encode spatial memories leads to formation of incorrect fear memory in mice

More information: "Neural Activity in Human Hippocampal Formation Reveals the Spatial Context of Retrieved Memories," by J.F. Miller et al. Science, 2013.

Related Stories

Modifying activity of neuronal networks that encode spatial memories leads to formation of incorrect fear memory in mice

September 13, 2013
The formation and retrieval of memories allows all kinds of organisms, including humans, to learn and thrive in their environment. Yet our memories are not always accurate, and mistaken remembrances can have important consequences, ...

The brain's GPS: Scientists find neurons linked to navigation in open environments

August 4, 2013
Using direct human brain recordings, a research team from Drexel University, the University of Pennsylvania, UCLA and Thomas Jefferson University has identified a new type of cell in the brain that helps people to keep track ...

Researchers show 'neural fingerprints' of memory associations

June 26, 2012
Researchers have long been interested in discovering the ways that human brains represent thoughts through a complex interplay of elec-trical signals. Recent improvements in brain recording and statistical methods have given ...

Researchers find neural signature of 'mental time travel'

July 18, 2011
Almost everyone has experienced one memory triggering another, but explanations for that phenomenon have proved elusive. Now, University of Pennsylvania researchers have provided the first neurobiological evidence that memories ...

Neuroscientists show ability to plant false memories

July 25, 2013
The phenomenon of false memory has been well-documented: In many court cases, defendants have been found guilty based on testimony from witnesses and victims who were sure of their recollections, but DNA evidence later overturned ...

How chronic pain disrupts short term memory

February 7, 2013
A group of Portuguese researchers from IBMC and FMUP at the University of Porto has found the reason why patients with chronic pain often suffer from impaired short –term memory. The study, to be published in the Journal ...

Recommended for you

Cognitive cross-training enhances learning, study finds

July 25, 2017
Just as athletes cross-train to improve physical skills, those wanting to enhance cognitive skills can benefit from multiple ways of exercising the brain, according to a comprehensive new study from University of Illinois ...

Brain disease seen in most football players in large report

July 25, 2017
Research on 202 former football players found evidence of a brain disease linked to repeated head blows in nearly all of them, from athletes in the National Football League, college and even high school.

Zebrafish study reveals clues to healing spinal cord injuries

July 25, 2017
Fresh insights into how zebrafish repair their nerve connections could hold clues to new therapies for people with spinal cord injuries.

Lutein may counter cognitive aging, study finds

July 25, 2017
Spinach and kale are favorites of those looking to stay physically fit, but they also could keep consumers cognitively fit, according to a new study from University of Illinois researchers.

Brain stimulation may improve cognitive performance in people with schizophrenia

July 24, 2017
Brain stimulation could be used to treat cognitive deficits frequently associated with schizophrenia, according to a new study from King's College London.

New map may lead to drug development for complex brain disorders, researcher says

July 24, 2017
Just as parents are not the root of all their children's problems, a single gene mutation can't be blamed for complex brain disorders like autism, according to a Keck School of Medicine of USC neuroscientist.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.