How our brain tracks movement


Whether we move ourselves or whether we watch someone else doing it – both trigger similar reactions in the brain. (Image: UCLA / Suthana lab)

As we move forward, a map of the environment is created in our brain, showing obstacles and boundaries. At the same time, we have to be able to register the movements of other people in our vicinity and to process them cognitively. But how are these signals coded? Researchers have now shown that specific activity patterns occur in the middle temporal lobe, the brain’s navigation system, when we approach walls. Amazingly, the same activity occurs when we watch another person explore the room. The mechanism could help us assess our own surroundings and the movements of other people.

Until now, researchers wanted to investigate how our brain behaves during movement and navigation tasks, but they were faced with a problem: Most of the techniques that can be used to observe brain activity only work if the test subject is lying in a tube or at least his head is in the process the brainwave measurement stops. Real movements were therefore not possible, virtual reality served as a makeshift. These studies, as well as research on rodents, suggest that the middle temporal lobe in the brain plays an important role in navigation. “But testing it further was technically difficult,” says Matthias Stangl from the University of California Los Angeles.

New technology for mobile brain wave measurement

Stangl and his colleagues have therefore solved the problem in a new way. They recruited people as test subjects who had had electrodes implanted in their brains due to epileptic seizures that could not be treated with medication. These measure brain activity and, if necessary, give off impulses that prevent a seizure. Stangl and colleagues developed a device that receives the data from these electrodes and that the test subjects can carry with them as a backpack.

“The backpack enables us to observe how the brain functions during natural movements,” explains Stangl’s colleague Uros Topalovic. Nanthia Suthana, who heads the research group, adds: “For the first time we were able to directly examine how a person’s brain navigates through an actual physical space that is shared with others. Our results suggest that our brains use a common code to know where we and others are in social environments. “

Brain waves show spatial boundaries

In their experiment, the researchers first asked their test subjects to walk through a room while the backpack received their brain waves and a device attached to the head tracked their eye movements. It showed that whenever the test subjects approached a wall, certain brain waves, so-called theta waves, intensified in the subjects’ temporal lobe. The test subjects received instructions via loudspeaker to go to a clearly visible sign on the wall or to look for a hidden target on the floor of the room. The purposeful movement was also reflected in a specific theta activity.

The experiment thus confirms indications from previous studies on rodents and humans in virtual reality. This also indicated that the brain creates a mental map in which walls or other boundaries trigger different activity patterns than free areas. “These results support the idea that, under certain mental states, theta rhythms can help the brain know where its limits are. In this case we are focused and looking for something, ”says Stangl. Based on further analyzes, the researchers were able to rule out that other factors such as eye or head movements had distorted the result.

The same activity pattern for your own and other people’s movements

To the surprise of the researchers, the same activity pattern was found when the test subject did not move through the room himself, but instead observed an experimenter. Meanwhile, the test person sat in a corner of the room. As a motivation to follow the movements carefully, he should press a button as soon as the experimenter reached the hidden goal – which was now known to the test subject. “Our results support the idea that our brains use a universal signature so that we can put ourselves in the shoes of others,” says Suthana.

This ability is regularly important in everyday life. “Everyday activities constantly require us to navigate the same place with other people,” explains Suthana. “Be it that we want to choose the shortest line for the security check at the airport, that we are looking for a place in a crowded parking lot to park our car, or that we don’t want to bump into other people on the dance floor.” They want such more complex social situations Researchers investigate in future studies. They are also making their new technology available to other research groups in order to enable further advances in research into the human brain.

Source: Matthias Stangl (University of California Los Angeles) et al., Nature, doi: 10.1038 / s41586-020-03073-y

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