Scientists discover a brain circuit that signals the direction and distance of boundaries in the environment

We perceive the world in relation to our body from a self-centered perspective. Yet our brain is able to transform this information into a world-centered cognitive map of the environment, guiding us no matter where we look or the direction we face. The mechanism behind this has remained unsolved for decades. Now scientists from the Max Planck Institute for Brain Research and Goethe University in Frankfurt are discovering a neural circuit in the rodent brains that can play a key role in translating both perspectives and help the animal detect boundaries to avoid collision.

“Animals use landmarks in the environment as a reference point to identify the position of the self and navigate the surrounding environment. In rodents, this ability is supported by very specialized types of neurons, including local cells and cells. of the grid, which are activated only when the animal is at a precise location in the environment, even in an open arena, “explains Hiroshi Ito, head of the research group on navigation and memory circuits and senior author of the new study.

The retrosplenial cortex is an area of ​​the brain that is important for processing fundamental information. However, the exact function of individual neurons in this brain region is still unknown. “By recording from the retrosplenial cortex in the rat, we discovered a new type of neuron that signals the location of room boundaries such as walls from the animal’s point of view,” says Joeri van Wijngaarden, lead author of the study. “The boundary cells fire with high accuracy. In this case, only when the boundary is at a particular distance and direction from the animal.” But how do border cells know when to be active? Do they use direct sensory signals, such as sight or whiskers, to detect walls? To answer this question, the researchers manipulated the animal’s sensory experience. “To our surprise, we didn’t see any difference when the mouse explored the maze in complete darkness. The cells continued firing as they did before,” says van Wijngaarden.

Interaction between boundary cells and spatial cells

Inspired by this unexpected discovery, the scientists set out to investigate how boundary cells interact with space cells in a connected brain region, the entorhinal cortex, which is critical for spatial processing and for forming an internal map of space. environment. “We recorded the activity of space cells in the entorhinal cortex while silencing the boundary cells in the retrosplenial cortex with a drug,” explains van Wijngaarden. “At first, we didn’t see any effect. However, when we shifted gears and instead silenced the space cells in the entorhinal cortex, we suddenly noticed a disruption of boundary cell activity in the retrosplenial cortex,” explains van Wijngaarden. “This was a big surprise as it suggests that boundary cells capture key information without the need to perceive it directly. Instead, they rely on spatial information from other areas of the brain to calculate their position.”

“What struck me the most, though,” van Wijngaarden shares, “is that there is a close relationship between the activity of these neurons and the subsequent movement of the animal. When the rat approaches a wall on the left, the Boundary cells in the right hemisphere are activated just before the animal turns right. Conversely, boundary cells in the left hemisphere are activated just before the left turn to avoid collisions. ” “These findings bring a whole new perspective to the field. They provide the first insight into how the internal brain map can be used to guide our movements while navigating. Hopefully, this will improve our understanding of how the brain makes sense of world around us to move from one place to another “, concludes Ito.