Scientists have found groups of cells that fire at different rates depending on how fast an animal is moving. Dubbed “speed cells,” they could be the missing link in how animals are able to pinpoint their own location.
The study, by scientists from the Norwegian University of Science and Technology, builds on earlier research that had identified two groups of neurons responsible for helping animals track their location. "Place cells," discovered in the 1970s, were found to fire when a rat entered a certain location. "Grid cells," meanwhile, found in 2005, fire at regular intervals when an animal moves, helping their brains create a grid with mental coordinates.
How these cells obtained information on the angle and speed of movement, though, had remained somewhat of a mystery. Now, the team writing in Nature Neuroscience say they have found evidence for previously hypothesized speed cells.
"The speed cells that we discovered are a kind of missing link in our understanding of how the positioning system works," co-author on the study Edvard Moser told IFLScience.
In experiments, rats were wired into a moveable treadmill and placed on a track four meters (13 feet) long. They were then made to run at certain speeds by changing the speed of the treadmill. Electrodes were implanted into the brains of the rats to study deep brain tissue known as medial entorhinal cortex (MEC), where grid cells had been found before.
The medial entorhinal cortex (MEC), shown by the yellow arrow, could be responsible for our in-built GPS. Hagmann P/Cammoun L/Gigandet X/Meuli R/Honey CJ et al/Wikimedia Commons.
During the tests, it was found that between 13 and 15% of the recorded cells showed a firing pattern that correlated with the speed the animals were running. The cells, numbering several hundred, seem to have no other purpose aside from monitoring the speed of the animal, Moser told IFLScience. "This is the first time that speed cells have been shown as a unique cell type," he said.
While this experiment was in rats, Moser said that it was "quite likely" these same positioning cells exist in humans. "We know that some grid cells exist in humans, it has been shown in epilepsy patients who have tiny electrodes implanted into their brain," he said. Place cells have also been detected in humans.
These are not exclusively the only types of positioning cells; "border cells" and "direction cells" have been detected before. But if we can successfully comprehend how they all work, it could have implications for treating certain conditions.
"They would complete a better understanding of how the cortex works," said Moser, "and the cortex is the basis of all activity, so this would be a much better basis for understanding psychiatric diseases." In particular, he notes that it could be useful in treating Alzheimer's disease, which can be accompanied by a loss of a sense of direction.
The next step for the research will be to work out exactly where the signals are coming from in the brain, and how the cells work together to create this in-built positioning system.