In a groundbreaking study, scientists have successfully pinpointed a “mileage clock” within the brain by meticulously recording the neural activity of running rats.
Researchers monitored a region crucial for navigation and memory as the rats explored a confined arena.
The team observed that specific cells exhibited a firing pattern akin to a mileage counter, registering activity with each successive step taken by the animal.
Subsequent research involving human participants traversing a scaled-up version of the rat navigation test indicated a similar mechanism exists within the human brain.
The study, published in the esteemed journal Current Biology, provides compelling evidence that the rhythmic activity of “grid cells” directly correlates with the ability to accurately assess distance traveled.
“Imagine navigating between your kitchen and living room,” explains lead researcher Professor James Ainge from the University of St Andrews. “[These cells] reside in the part of the brain responsible for that internal map – the capacity to mentally place yourself within the environment.”
This research sheds light on the inner workings of our brain’s internal map and the potential ramifications when this system malfunctions. Disrupting the mileage clock’s rhythmic activity through environmental manipulation leads to distance estimation errors in both rats and humans.
This phenomenon manifests in real-world scenarios such as navigating in darkness or dense fog, where the absence of visual cues compromises our ability to reliably gauge distances.
To empirically examine this, researchers trained rats to run a predetermined distance within a rectangular arena, rewarding accurate completion with a piece of chocolate cereal.
When the rats accurately traversed the target distance, the mileage-counting cells exhibited regular firing patterns, occurring approximately every 30cm traveled.
“The more consistent the firing pattern, the more proficient the animals became at judging the required distance for the reward,” Professor Ainge elaborated.
The researchers were able to document the brain’s mileage clock as it precisely tracked the distance covered by the rat.
Importantly, alterations to the shape of the arena disrupted the regular firing patterns, causing the rats to struggle in accurately determining the distance back to the starting point for their reward.
“It’s quite remarkable,” Professor Ainge stated. “They appear to exhibit a consistent underestimation. The irregularity of the signal seems to cause them to stop prematurely.”
The scientists drew a parallel to the sudden disappearance of visual landmarks in foggy conditions.
“While it’s widely understood that fog makes navigation challenging, it’s perhaps less appreciated that it also significantly impairs our ability to accurately estimate distance.”
To validate these findings in humans, the researchers replicated their rat experiment on a larger scale, constructing a 12m x 6m arena within the university’s student union. Volunteers were tasked with performing the same task as the rats – walking a specific distance and returning to the origin.
Mirroring the rat’s performance, the human participants consistently and accurately estimated the distance within a symmetrical, rectangular enclosure. However, when the researchers manipulated the arena’s shape by repositioning the walls, the participants began to make errors.
Professor Ainge noted: “Rats and humans demonstrate rapid learning in the distance estimation task. However, when the environment is altered in a way known to distort the signal in rats, we observe an identical behavioral pattern in humans.”
Beyond providing valuable insights into human navigation, the scientists suggest that their findings could contribute to the early diagnosis of Alzheimer’s disease.
“The specific brain cells being monitored are located in one of the primary regions affected by Alzheimer’s,” Professor Ainge explained.
“Diagnostic tools, such as mobile games designed to assess navigation, are already available. We are keenly interested in exploring similar approaches, with a particular focus on evaluating distance estimation abilities.”
To delve deeper into this topic, listen to Victoria Gill’s report on BBC’s Inside Science.
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