Grid cells not only help us navigate our own paths in a complex environment, but also help us analyse the movements of other people, scientists from the University of Vienna have now shown for the first time. Their new study in Nature Communications also suggests an explanation for a mechanism that could lead to disorientation in dementia patients.
Whether you are making your way through a crowded pedestrian zone or striving towards the goal in a team game, in both situations it is important to think not only about your own movements but also those of others. These navigation and orientation processes are carried out by brain cells that register our current position, where we are coming from, where we are moving towards and in which direction we are looking. Through their joint activity, they create a "map" of our surroundings. A special type of these cells are the so-called grid cells in the entorhinal cortex, a small brain region in the middle temporal lobe. They function like the brain's own GPS, because they not only represent our position in space, but can also put it in relation to other points in the same space.
Whether these grid cells are also involved in mapping the movements of other individuals on this map was the question that the scientists led by Isabella Wagner and Claus Lamm from the Faculty of Psychology at the University of Vienna addressed. For this purpose, the scientists tested participants that either navigated themselves in a virtual environment, or observed the movements of another person while their brain activity was measured using functional magnetic resonance imaging (fMRI).
They found that the brain activity recorded while watching others was comparable to the activity of grid cells. In addition, the team was able to show that this activity was part of a larger network of brain regions that are associated with navigation processes. Interestingly, however, it turned out that the better a subject was at following the path of others, the less active this network was. "We interpret this as greater efficiency of the grid cells, which might make it less necessary to engage the larger brain network," Wagner explains.
The results of the study thus suggest that grid cells belong to a larger network of brain regions that, among other aspects, coordinates navigation processes. However, this network is particularly affected by ageing processes and especially by dementia. Wagner explains: "The function of grid cells decreases with age and dementia. As a result, people can no longer find their way around and their orientation is impaired." The group's further research is now dedicated to the question of whether grid cells are also involved in recognising other people - an aspect that is often impaired in advanced dementia.
Entorhinal grid-like codes and time-locked network dynamics track others navigating through space
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