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NATURAL SCIENCE

'Grid cells' help rats, humans with navigation, researchers say

  • Grid neurons in the brain activate during navigation to help humans keep track of where they are, scientists say.Drexel University

  • Scientists study an MRI targeting the area of the hippocampus where electrodes were placed.John F. Burke

Like a GPS in your brain, a newly discovered type of cell helps people keep track of their location while navigating an unfamiliar environment, researchers say.

Using direct human brain recordings, scientists from Drexel University, the University of Pennsylvania, UCLA and Thomas Jefferson University found the “grid cell,” so called for its triangular grid pattern.

This grid pattern, which needs to be consistent, is critical as it shows how people can keep track of their location even in new environments, notes Joshua Jacobs, an assistant professor from Drexel and the study’s primary investigator.

“Without grid cells, it's likely that humans would frequently get lost or have to navigate based only on landmarks. Grid cells are thus critical for maintaining a sense of location in an environment," Jacobs explained.

The cell is activated during navigation and allows the brain to keep track of navigational cues, such as how far a person is from their starting point and their last turn. Navigation in this manner is known as path integration.

The team, which included Michael Kahana of Penn, and Itzhak Fried of UCLA, discerned the cells after having a rare opportunity to study brain recordings of epileptic patients.

With electrodes placed deep inside their brains, 14 participants played a video game, challenging them to navigate from one point to another, collecting objects while riding a virtual bicycle. They then had to recall how to how to get back to places where each object was located.

After trail runs – with each of the objects visible by the gamers in the distance – they were returned to the start of the game and the objects were hidden until the virtual bicycle was right in front of them. Scientists then told the participants to travel to particular objects in different orders.

After studying the relationship between navigation and the activity of individual neurons, Jacobs stated that the triangular grid pattern appears to play a fundamental role in navigation.

The findings in this experiment mark the first positive identification of such cells in humans. Prior experiments showed the existence of grid cells in rats and human hippocampal place cells, according to Kahana, a professor of psychology. The new findings also suggest that grid patterns may be more prevalent in humans. Human grid cells were found in the entorhinal cortex – same as the rats – but also in the cingulate cortex.

The entorhinal cortex is a critical part of the human memory system and the findings will hopefully shed new light on a region of the brain that is first to be affected in Alzheimer's disease, according to Fried.

It could also help researchers understand why people with Alzheimer’s often become disoriented, while showing them how to improve brain function of people with this disease, Jacobs explained