By Victoria Gill
Copyright bbc
To investigate this experimentally, researchers trained rats to run a set distance in a rectangular arena – rewarding the animals with a treat – a piece of chocolate cereal – when they ran the correct distance and then returned to the start.
When the animals ran the correct distance, the mileage-counting cells in their brains fired regularly – approximately every 30cm a rat travelled.
“The more regular that firing pattern was, the better the animals were at estimating the distance they had to go to get that treat,” explained Prof Ainge.
The researchers were able to record the brain’s mileage clock counting the distance the rat had moved.
Crucially, when the scientists altered the shape of the rat arena, that regular firing pattern became erratic and the rats struggled to work out how far they needed to go before they returned to the start for their chocolate treat.
“It’s fascinating,” said Prof Ainge. “They seem to show this sort of chronic underestimation. There’s something about the fact that the signal isn’t regular that means they stop too soon.”
The scientists likened this to visual landmarks suddenly disappearing in the fog.
“Obviously it’s harder to navigate in fog, but maybe what we what people don’t appreciate is that it also impairs our ability to estimate distance.”
To test this in humans, the researchers scaled up their rat-sized experiment. They built a 12m x 6m arena in the university’s student union and asked volunteers to carry out the same task as the rats – walking a set distance, then returning to the start.
Just like rats, human participants were consistently able to estimate the distance correctly when they were in a symmetrical, rectangular box. But when the scientists moved the walls of their purpose-built arena to change its shape, the participants started making mistakes.
Prof Ainge explained: “Rats and humans learn the distance estimation task really well, then, when you change the environment in the way that we know distorts the signal in the rats, you see exactly the same behavioural pattern in humans.”
