Amazing stuff!
"Scientists have for the first time located the "mileage clock" inside a brain - by recording the brain activity of running rats.
Letting them loose inside a small, rat-sized arena, the researchers recorded from a part of their brains that is known to be important in navigation and memory.
They found that cells there "fired" in a pattern that looked like a mileage clock - ticking with every few steps the animal travelled.
A further experiment, where human volunteers walked through a scaled up version of this rat navigation test, suggested that the human brain has the same clock. ..."
"... Previous studies have shown that some of these cells have very regular peaks of activity, approximately every 30cm, like a neural pedometer. ... researchers then changed the task environment so that the peaks of activity were less regular and found that the rats’ ability to estimate distance got worse. ..."
"In new research ... trained rats to run a specific distance to get a reward. They then recorded from individual cells in the brain’s navigation system as the rats performed the task. Previous studies have shown that some of these cells have very regular peaks of activity, approximately every 30cm, like a neural pedometer. St ... researchers then changed the task environment so that the peaks of activity were less regular and found that the rats’ ability to estimate distance got worse. ...
The measurements were recorded in the brain’s entorhinal cortex. This is one of the very first areas of the brain to be damaged in Alzheimer’s disease. This means that the distance estimation task that relies on the neural pedometer might be a useful tool for early diagnosis. ..."
From the abstract:
"Highlights
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Distance estimation is impaired in trapezoids, but not rectangles, in rats and humans
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Grid cell symmetry is distorted in trapezoidal, but not rectangular, environments
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Grid cell distortion is correlated with distance estimation error
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Experience of a trapezoid distorts grid cell symmetry in future experiences
Summary
Grid cells within the medial entorhinal cortex (MEC) exhibit a regular hexagonal pattern of firing fields, which has been hypothesized to provide a universal spatial metric, supporting spatial memory and navigation. This could be used to support a cognitive map, our internal representation of external space, and consistent with this, disruption of the MEC impairs spatial memory and place cell anchoring to external visual cues. However, the highly regular and repetitive nature of the firing fields in grid cells is also ideally suited to support path integration.
Indeed, genetic silencing of stellate cells in MEC results in impaired distance estimation, supporting the MEC’s role in path integration.
However, few studies have examined the role of grid cell firing during active navigation.
Several studies have reported that manipulation of environmental cues, recent experience, and reward location distort the grid signal, but most relevant here is that the grid signal distorts in polarizing environments, such as trapezoids.
If grid cells support distance estimation and path integration, then disruption of the grid regularity, such as that seen in polarized environments, should impair these processes.
Here, we report that both rats and humans have impaired distance estimation in polarized environments. Grid regularity was again reported to be distorted in polarized environments, and this was correlated with impaired distance estimation in rats. Grid regularity was also distorted by recent experience. These findings are consistent with grid cells supporting distance estimation in navigation."
Study reveals brain’s built-in distance tracker (original news release)
Figure 1 Rats and humans overestimate distance traveled in the trapezoid-shaped environment
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