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Researchers find that the brain can optimize its navigation system without landmarks

Researchers find that the brain can optimize its navigation system without landmarks
Researchers find that the brain can optimize its navigation system without landmarks

Brains can optimize their navigation system without landmarks

Stripe representation and gain calculation. a, Virtual reality dome apparatus b, Stripes projected in the dome. c, Stripe gain S related to the rat’s speed with respect to the laboratory and stripe images. d–g, Hippocampal gain decoding. h, Spatial information values ​​in the hippocampal image are significantly higher than those in the laboratory and stripe image for each rat. Image credit: Natural Neuroscience (2024). DOI: 10.1038/s41593-024-01681-9

Research from Johns Hopkins University sheds new light on how mammals track their position and orientation during movement, showing that visual motion cues alone allow the brain to adjust and recalibrate its internal map, even in the absence of stable visual landmarks.

The results are published in Natural Neuroscience.

“As you move through space, you’re faced with a lot of competing sensory information telling you where you are and how fast you’re moving. Your brain has to process that,” said study co-leader Noah Cowan, a professor of mechanical engineering in the Whiting School of Engineering and director of the Locomotion in Mechanical and Biological Systems (LIMBS) Laboratory.

“The results of our study show that, surprisingly, the brain can perform this continuous recalibration without any obvious external landmarks telling us our position. The brain can adjust its internal sense of speed through its spatial map, based solely on cues from optic flow: the visual motion patterns that people perceive as they move through space.”

Cowan collaborated on the project with James Knierim, professor of neuroscience at the Zanvyl Krieger Mind/Brain Institute of the Krieger School of Arts and Sciences and the Kavli Neuroscience Discovery Institute at Johns Hopkins University.

For example, researchers knew that when a person walks through a tunnel covered with markers, their brain detects the speed at which the markers appear to move past, helping them estimate the distance traveled and their relative position in space.

The team wanted to find out whether changing the speed at which the markers passed the hiker or removing the markers would significantly affect the brain’s response.

“We wanted to figure out how our brain calculates distance traveled using only speed information,” Cowan said. “Neurons in our hippocampus light up like the blue GPS dot on your phone. We hypothesized that the relationship between optic flow and the blue dot update could be recalibrated in virtual reality – and we found that it can.”

Knierim explained that the researchers wanted to find out whether they could reliably control a lab rat’s sense of location on its cognitive map by artificially altering the amount of optic flow it receives in a virtual reality system.

“We found that we could use the principles of control theory to precisely control the cognitive map using only optical flow signals, demonstrating that this long-suspected input was indeed used by the rat’s path integration system,” Knierim said.

The team constructed a virtual reality dome and projected glowing stripes onto the walls. Rats were lured to run around the dome by dripping chocolate milk. The stripes were intended to serve as a subconscious cue to the rodents’ speed and approximate location in the room.

When the team set the stripes to rotate in the opposite direction to the rats as they walked, the response of the animals’ hippocampus suggested that they thought they were moving twice as fast and their sense of location was distorted.

When the strips were turned off after a certain period of time, the researchers found that the rats still moved faster than they actually did.

Cowan said it was already known that mammalian brains use the position of landmarks relative to each other to determine location and calibrate approximate speed. What was not known, however, was whether a mammal’s brain would recalibrate its speed using its mental map if there were no landmarks.

“How your brain performs this recalibration without landmarks, and that it does it at all, was not known until now, and that’s what we show in this research,” he said.

The study’s findings provide valuable insights in two key areas. First, they shed light on how the mammalian hippocampus works, a brain region implicated in Alzheimer’s disease and other dementias, and second, the research answers a long-standing question about the basic biology of how animals navigate the world.

“Because the navigation system is so closely linked to the brain’s memory system, we hope that understanding how it creates these cognitive maps will give us insight into how memory declines in old age and dementia,” Knierim said.

But the results also have implications for robotics. Cowan noted that the findings could also influence the development of AI and machine learning algorithms that integrate visual information with spatial representations, ultimately paving the way for embodied cognitive systems.

More information:
Manu S. Madhav et al, Controlling and recalibrating path integration in place cells using optic flow, Natural Neuroscience (2024). DOI: 10.1038/s41593-024-01681-9

Provided by Johns Hopkins University

Quote: Researchers find that brains can optimize their navigation system without landmarks (June 28, 2024), accessed June 28, 2024 from https://medicalxpress.com/news/2024-06-brains-tune-landmarks.html

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