Left: Screenshot of spatial memory task. Right: MRI scan showing the placement...
Left: Screenshot of spatial memory task. Right: MRI scan showing the placement of recording electrodes (black circles) in a patient's brain.
19.11.2019 •

Neurons that map memories identified using VR

Scientists correlate neuronal activity in the human entorhinal cortex with place-based memories; finding sheds new light on how the brain processes spatial memory.

An important aspect of human memory is our ability to conjure specific moments from the vast array of experiences that have occurred in any given setting. For example, if asked to recommend a tourist itinerary for a city you have visited many times, your brain somehow enables you to selectively recall and distinguish specific memories from your different trips to provide an answer.

Studies have shown that declarative memory—the kind of memory you can consciously recall like your home address or your mother’s name—relies on healthy medial temporal lobe structures in the brain, including the hippocampus and entorhinal cortex (EC). These regions are also important for spatial cognition, demonstrated by the Nobel-Prize-winning discovery of “place cells” and “grid cells” in these regions—neurons that activate to represent specific locations in the environment during navigation (akin to a GPS). However, it has not been clear if or how this “spatial map” in the brain relates to a person’s memory of events at those locations, and how neuronal activity in these regions enables us to target a particular memory for retrieval among related experiences.

A team led by neuroengineers at Columbia Engineering has found the first evidence that individual neurons in the human brain target specific memories during recall. They studied recordings in neurosurgical patients who had electrodes implanted in their brains and examined how the patients’ brain signals corresponded to their behavior while performing a virtual-reality (VR) object–location memory task. The researchers identified “memory-trace cells” whose activity was spatially tuned to the location where subjects remembered encountering specific objects.

“We found these memory-trace neurons primarily in the entorhinal cortex, which is one of the first regions of the brain affected by the onset of Alzheimer’s disease,” says Joshua Jacobs, associate professor of biomedical engineering, who directed the study. “Because the activity of these neurons is closely related to what a person is trying to remember, it is possible that their activity is disrupted by diseases like Alzheimer’s, leading to memory deficits. Our findings should open up new lines of investigation into how neural activity in the entorhinal cortex and medial temporal lobe helps us target past events for recall, and more generally how space and memory overlap in the brain.”

Conceptual illustration of neurons that “map” memories in the human brain.
Conceptual illustration of neurons that “map” memories in the human brain.

The team was able to measure the activity of single neurons by taking advantage of a rare opportunity: invasively recording from the brains of 19 neurosurgical patients at several hospitals, including the Columbia University Irving Medical Center. The patients had drug-resistant epilepsy and so had already had recording electrodes implanted in their brains for their clinical treatment. The researchers designed experiments as engaging and immersive VR computer games and the bedridden patients used laptops and handheld controllers to move through virtual environments. In performing the task, subjects first navigated through the environment to learn the locations of four unique objects. Then the researchers removed the objects and asked patients to move through the environment and mark the location of one specific object on each trial.

The team measured the activity of neurons as the patients moved through the environment and marked their memory targets. Initially, they identified purely spatially tuned neurons similar to “place cells” that always activated when patients moved through specific locations, regardless of the subjects’ memory target. “These neurons seemed only to care about the person’s spatial location, like a pure GPS,” says Salman E. Qasim, Jacobs’ PhD student and lead author of the study.

But the researchers also noticed that other neurons only activated in locations relevant to the memory the patient was recalling on that trial—whenever patients were instructed to target a different memory for recall, these neurons changed their activity to match the new target’s remembered location. What especially excited Jacobs and Qasim is that they could actually decode the specific memory a patient was targeting based on the activity of these neurons. “Our study demonstrates that neurons in the human brain track the experiences we are willfully recalling, and can change their activity patterns to differentiate between memories. They’re just like the pins on your Google map that mark the locations you remember for important events,” Qasim says. “This discovery might provide a potential mechanism for our ability to selectively call upon different experiences from the past and highlights how these memories may influence our brain’s spatial map.”

Jacobs and Qasim plan next to look for evidence that these neurons represent memories in non-spatial contexts to better characterize their role in memory function. “We know now that neurons care about where our memories occur and now we want to see if these neurons care about other features of those memories, like when they occurred, what occurred, and so on,” Qasim notes.

Subscribe to our newsletter

Related articles

VR study: our visual world of color is incorrect

VR study: our visual world of color is incorrect

A study finds that people are aware of surprisingly limited color in their peripheral vision; much of our sense of a colorful visual world is likely constructed by our brain.

VR for early detection of MS balance problems

VR for early detection of MS balance problems

The UNC School of Medicine lab of Jason Franz, PhD, created virtual reality experiments to show how a potentially portable and inexpensive test could reduce falls and related injuries in people with multiple sclerosis.

VR supports the treatment of children with brain injury

VR supports the treatment of children with brain injury

Research confirms the efficiency of using computer-based programmes and virtual reality for improving children's attention and social skills.

Is virtual reality not suited to visual memory?

Is virtual reality not suited to visual memory?

Researchers have found that virtual reality may interfere with visual memory.

Barking up the wrong tree with virtual reality

Barking up the wrong tree with virtual reality

Researcher used virtual reality to trick 20 patients with with intermittent arterial claudication, and discovered that they could suddenly walk much further.

Virtual “moonwalk” for science

Virtual “moonwalk” for science

In order to orient ourselves in space, and to find our way around, we form mental maps of our surroundings. Scientists used VR to detect distortions in our spatial memory.

Brain may not need body movements to learn virtual spaces

Brain may not need body movements to learn virtual spaces

A new study enhances our understanding of how the brain learns in virtual reality.

Virtual treasure hunt shows brain maps time sequence of memories

Virtual treasure hunt shows brain maps time sequence of memories

Combining learning in virtual reality and brain scans, researchers describes how a temporal map of memories is created in the entorhinal cortex.

VR helps to identify brain areas involved in a memory

VR helps to identify brain areas involved in a memory

Researchers used a virtual reality environment to train subjects, then showed that different areas of the hippocampus are activated for different types of memories.

Popular articles