ISLAMABAD: Scientists have finally identified the internal mileage clock of the brain by tracking the brain activity of the running rats.
The researchers put the rats into a small, specially designed arena and monitored activity in an area of the brain that is already known to be relevant to memory and navigation.
They found that some brain cells were activated in a regular pattern, which resembled an inbuilt odometer – they ticked at a regular rate as the rats moved along.
In a follow-up experiment, human volunteers were used in a scaled version of the rat maze, and the findings indicated that our brains apply a similar process to estimate distance.
Results
The results, which were reported in Current Biology, are the first instance that scientists have demonstrated a definite connection between the rhythmical firing of the so-called grid cells and our capacity to determine how far we have travelled.
“Imagine walking between your kitchen and living room,” said Professor James Ainge from the University of St Andrews, who led the study. “[These cells] are in the part of the brain that provides that inner map – the ability to put yourself in the environment in your mind.”
The research offers a fresh understanding of the way this internal map works – and what occurs when it fails. As the researchers changed the arrangement of the surroundings, the rats, as well as the human participants, started to misjudge distance, which implied that the mileage clock was not ticking as well.
Confusion in normal life scenarios
This type of confusion may occur in normal life scenarios where visibility is low, such as in darkness or heavy fog. In the absence of visual stimuli, our internal sense of distance is far less precise.
To measure this more accurately, the group conditioned rats to run a certain distance in a rectangular arena. When they ran the right distance and went back to the starting point, they would be given a small piece of chocolate cereal.
The brain scans revealed that the mileage cells of the rats were active in a constant manner, that is, approximately every 30cm covered by the rats when they estimated the distance correctly.
“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.
Altering shape
However, when the shape of the arena was altered, the regular firing pattern became disrupted. As a result, the rats struggled to judge how far to run before returning for their 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 effect is similar to what happens when familiar visual landmarks disappear, such as during foggy conditions.
“Obviously, it’s harder to navigate in fog, but maybe what people don’t appreciate is that it also impairs our ability to estimate distance.”
Invalid estimates
The researchers repeated the experiment on a larger scale to determine whether humans would act similarly by constructing a 12m by 6m arena in the student union at St Andrews and requesting volunteers to walk a specified distance and back to the starting point.
Similar to the rats, the participants could judge distances well in a normal rectangular area. However, their estimates were invalid when the walls were shifted and the form of the space altered.
Prof Ainge: Rats and humans are very good at the distance estimation task, and then, when you manipulate the environment in the manner that we know distorts the signal in the rats, you observe precisely the same behavioural pattern in humans.
Diagnosis of Alzheimer’s
Besides aiding us in comprehending the role of the brain in aiding navigation, the study could also be used in the diagnosis of Alzheimer’s disease.
“The specific brain cells we’re recording from are in one of the very first areas that’s affected in Alzheimer’s,” explained Prof Ainge.
“People have already created [diagnostic] games that you can play on your phone, for example, to test navigation. We’d be really interested in trying something similar, but specifically looking at distance estimation.”
