Researchers in psychology and neuroscience are working to connect specific regions of the brain with behaviors and abilities that depend on them. While advances in non-invasive imaging technologies have propelled this interdisciplinary work forward, there is no substitute for directly recording the electrical activity of the living brain.
The logistics of placing electrodes deep in the brain usually make it impossible for people to volunteer to participate in such experiments. However, a Penn-led research team recently capitalized on a rare opportunity to study direct brain recordings by recruiting epilepsy patients who already had electrodes implanted on their brain as part of their treatment.
By measuring the brain activity of these patients while they played a simple video game, the researchers identified a new type of cell that helps people keep track of their relative location while navigating an unfamiliar environment.
The research was led by Michael Kahana, a professor in the Department of Psychology in the School of Arts & Sciences, and his former graduate student, Joshua Jacobs, who is now at Drexel. They collaborated with researchers at UCLA and Thomas Jefferson University.
The 14 study participants played a video game that involved riding a virtual bicycle around an open field to specific locations marked by objects. After trial runs during which the objects were visible in the distance, participants were returned to the center of the map, and the objects were hidden. The researchers then asked the participants to travel to particular objects in different sequences.
The team studied the relation between how the participants navigated in the video game and the activity of individual neurons. The cells they identified are known as “grid cells,” named for the triangular grid pattern in which they activate during navigation. Firing at multiple locations at once allows the brain to keep track of navigational cues, such as the distance traveled from a starting point or from the last turn.
“Without grid cells, it is likely that humans would frequently get lost or have to navigate based only on landmarks,” Jacobs says.
This is the first positive identification of human grid cells, building upon earlier non-invasive studies, as well as direct studies on rats.
“The present finding of grid cells in the human brain, together with the earlier discovery of human hippocampal ‘place cells,’ which fire at single locations, provide compelling evidence for a common mapping and navigational system preserved across humans and lower animals,” Kahana says.