For the first time, scientists have recorded how our brain moves through physical space and follows someone else’s place. The researchers used a special backpack to wirelessly monitor the brain waves of patients with epilepsy as they all walked around the empty room in search of a two-meter hidden spot.
In an article published in Nature, scientists report that the waves flowed in a different pattern suggesting that each individual’s brain drew walls and other boundaries.
Interestingly, each participant’s brain waves flowed in a similar way when they sat in a corner of the room and watched someone else walk, suggesting that these waves were also used to track other people’s movements. The study was part of NIH’s brain research through the advancement of Innovative Neurotechnologies® (BRAIN).
For the first time, we were able to directly study how a person’s brain manages the actual physical space that is shared with others. Our results suggest that our brains can use a common code to find out where we and others are in social settings.. “
Nanthia Suthana, PhD, Senior Study Author and Assistant Professor of Neurosurgery and Psychiatry at David Geffen School of Medicine, University of California, Los Angeles
Laboratory of dr. Suthane studies how the brain controls learning and memory. In this study, her team worked with a group of participants with drug-resistant epilepsy, aged 31-52 years, whose brains were surgically implanted with seizure control electrodes.
The electrodes are located in a memory center in the brain called the medial temporal lobe, which is also thought to control navigation, at least in rodents.
Over the past half century, scientists, including three Nobel Prize winners, have discovered – experiment after experiment – that neurons in this lobe, better known as network cells and set cells, act as a global positioning system. Moreover, scientists have found that the waves of low-frequency nerve activity of these cells, called theta rhythms, help rodents know where they and others are as they run through a maze or swim around a shallow pool of water.
“Several indirect pieces of evidence support the role of the medial temporal lobe in the way we move. But further testing of these ideas was technically difficult,” said Dr. Matthias Stangl, a postdoctoral fellow at UCLA and lead author of the article.
This study provides the most direct evidence to date that supports these ideas in humans, and is made possible by a special backpack provided by Dr. Suthane invented as part of the NIH BRAIN Initiative project.
“Many of the most important discoveries in brain research have been driven by technological advances. It is the NIH BRAIN initiative. It challenges researchers to create new tools and then use those tools to revolutionize our understanding of the brain and brain disorders,” said Dr. John Ngai, director of the NIH Brain Initiative.
At its core, the backpack contained a computer system that could be connected wirelessly to electrodes surgically implanted in the patient’s head. Recently, researchers showed that a computer can be connected to several other devices at the same time, including virtual reality glasses, eye tracks and monitors for the heart, skin and breathing.
“So far, the only ways to directly study human brain activity have required the subject to be still, whether lying in a massive brain scanner or plugged into an electrical imaging device.
In 2015, dr. Suthana approached me with the idea of solving this problem and so we took the opportunity to make backpacks, “said Uros Topalovic, MS, a UCLA graduate and author of the study.” The backpack frees the patient and allows us to study how the brain works during natural movements. “
To examine the role of the medial temporal lobe in navigation, the researchers asked study participants to put on a backpack and enter an empty room of 330 square meters.
Each wall was lined with a row of five colored characters with numbers from 1 to 5, one color per wall. A speaker mounted through the ceiling, a computerized voice asked the patient to approach one of the signs. When they reached the sign, a voice then asked them to look for a two-meter-diameter spot hidden somewhere in the room. Meanwhile, the backpack recorded the patient’s brain waves, pathways through the room, and eye movements.
In the beginning, it took each person a few minutes to find a place. During subsequent examinations, time shortened as their memory of the location improved.
Electrical imaging revealed a clear pattern of brain activity. Theta rhythms flowed harder – with higher peaks and lower valleys – as participants approached the wall than as they wandered in the middle of the room.
This happened only when they were looking for a place. In contrast, the researchers did not see an association between the strength of the theta rhythm and location when participants followed the walking instructions to the colored signs on the wall.
“These results support the idea that in certain mental states, theta rhythms can help the brain know where the boundaries are. In this case, it’s when we are focused and looking for something,” said Dr. Stangl.
Further analysis supported this conclusion and helped rule out the possibility that the results were caused by other factors, such as activities associated with different eye, body, or head movements.
Interestingly, they saw similar results when participants watched someone looking for a place. In these experiments, participants would sit on a chair in the corner of the room with backpacks and hands resting near the keyboard. Patients knew the location of the hidden place and pressed a button on the keyboard whenever another person came to it.
Again, participants ’brain waves flowed most strongly when the other person approached a wall or spot, and this pattern appeared only when the person was hunting, not following specific instructions.
“Our results support the idea that our brain can use these wavy patterns to put itself in another person’s shoes,” said Dr. Suthana. “The results open the door for us to help us understand how our brains control navigation and, perhaps, other social interactions.”
Tim dr. Suthane plans to explore these ideas in more detail. In addition, the team made the backpack available to other researchers who want to learn more about the brain and brain disorders.
This year, more than 175 research groups received funding from the NIH to support a wide range of projects, from mapping neural circuits that control what an octopus sees to helping people with paralyzed spinal cord injuries regain movement by upgrading computer programs powered by neural stimulation devices.
NIH / National Institute of Neurological Disorders and Stroke
Stangl, M., and others. (2020) Neural mechanisms anchored within location coding boundaries for self and others. Nature. doi.org/10.1038/s41586-020-03073-y.