Are you able to quickly make your way around a foreign city or do you feel lost as if navigating an endless labyrinth? Some people are certainly better at navigating their surroundings than others, and that’s likely due to how their ‘internal compass’ is wired in the brain.
It was only a few years ago that researchers confirmed that such a signal exists in a part of the brain called the entorhinal region. Now, thanks to the latest advances in brain imaging techniques, researchers have tracked neural activity in the part of the brain responsible for our sense of direction. By doing so, they have shed light on how the brain orients itself in changing environments, and even how it can be impacted by degenerative diseases like dementia.
Visual Information and the Brain’s Internal Compass
According to Mark Brandon, an Associate Professor of Psychiatry at McGill University and researcher at the Douglas Research Centre, neuroscience research has experienced a technological revolution over the last decade. This revolution has allowed scientists to ask and answer questions that were previously only dreamt of.
To understand how visual information impacts the brain’s internal compass, researchers exposed mice to a disorienting virtual world while they recorded the brain’s neural activity in minute detail.
By using the latest advances in neuronal recording technology, the team was able to simultaneously measure the activity of hundreds of head direction (HD) cells — a specialized group of brain cells involved in navigation — which accurately told them which way the rodent’s head was facing with an error of only a few degrees.
During the experiment, mice were placed in a special circular chamber where all the walls were covered by a full 360-degree LED screen. At first, a vertical white line was displayed. Then, in some versions of the experiment, the line would disappear for two-minute intervals and reappear shifted 90 degrees away around the chamber, as if the world had suddenly rotated around the mouse by 90 degrees. In other versions, the line would continuously rotate around the chamber.
While the rodents were subjected to a dizzying changing environment, the researchers studied how the head direction cells reacted using a method called calcium imaging.
The team’s ability to accurately decode these head direction cells — the building blocks of the brain’s internal compass — shows how the brain is capable of reorienting itself in changing surroundings.
The researchers also identified a phenomenon they call ‘network gain,’ which allowed the brain’s internal compass to reorient after the mice were disoriented. According to Zaki Ajabi, a former student at McGill University and now a postdoctoral research fellow at Harvard University, “it’s as if the brain has a mechanism to implement a ‘reset button’ allowing for rapid reorientation of its internal compass in confusing situations.”
They also learned that when a mouse sees a visual cue and then it disappears, its head direction cells keep track of which direction the cue came from. This way, these visual memory traces may help stabilize the internal head direction representation even when reliable visual cues are temporarily missing.
Implications for Virtual Reality and Alzheimer’s Disease
While the animals in this study were exposed to unnatural visual experiences, the authors argue that such scenarios are already relevant to the modern human experience, especially with the rapid spread of virtual reality technology. The findings “may eventually explain how virtual reality systems can easily take control over our sense of orientation,” adds Ajabi.
But the implications of this research are even more far-reaching and could prove key to treating patients with Alzheimer’s disease. According to Brandon, “one of the first self-reported cognitive symptoms of Alzheimer’s is that people become disoriented and lost, even in familiar settings.”
Researchers expect that a better understanding of how the brain’s internal compass and navigation system works will lead to earlier detection and better assessment of treatments for Alzheimer’s disease.
“The results of this study inspired the research team to develop new models to better understand the underlying mechanisms. “This work is a beautiful example of how experimental and computational approaches together can advance our understanding of brain activity that drives behavior,” says co-author Xue-Xin Wei, a computational neuroscientist and an Assistant Professor at The University of Texas at Austin.
The findings appeared in the journal Nature.
