Scientists at the Norwegian University of Science and Technology (NTNU) have discovered a part of the brain in animals that acts as a natural 'speedometer,' allowing them to regulate how fast or how slow they move.
NTNU researchers May-Britt Moser and Edvard Moser led the way in a seven-year study of the intricate navigation system of the brain. The Mosers were awarded the Nobel Prize in Physiology or Medicine last year for their discovery of grid cells in the system of the brain that fire according to an individual's position in space.
Previous research has suggested the presence of cells related to navigation that typically activate whenever an animal reaches a particular location. These so-called "place cells" are then followed by the activation of other neurons to indicate changes in the direction in which the head of the animal is facing.
The concept behind the place cells were first posited by University College London researcher John O'Keefe in the 1970s. O'Keefe shared the Nobel Prize with the Mosers.
These various cells would then send information to the brain to help it produce an internal map of the animal's location, but it is the "speed cells" that allow the individual's brain to update the map in real time.
To understand the function of these speed cells, the Mosers and their colleagues placed tiny electrodes into the brains of 26 individual rats, specifically around the structure of the entorhinal cortex where the grid cells are located. The electrodes the researchers implanted were sensitive enough to identify signals from specific neurons.
The rats were trained to run in a small car without a bottom, similar to how the characters in the Flintstones operate their vehicles, according to the Mosers. The cars were then placed on rails and run on a four-meter track depending on the speeds set by the researchers.
The researchers measured the brain responses from the rats every time they were made to move the car using a chocolate treat. They also recorded the animals' responses without physical constraints by allowing them to roam in an open area. In between each session, the rodents were allowed to rest inside flowerpots.
The Mosers and their team were able to document 2,497 cells in the structure of the entorhinal cortex after more than 2,000 sessions. They discovered that around 15 percent of these recorded cells were considered speed cells that fired faster or slower depending on the speed of the rat. These speed cells activated regardless of which direction the rats went, or whether the room they were in was dark or bright.
The findings show the accuracy of the speed cells, in which they are fully dedicated to detecting the speed of the individual. The cells responded strongly, allowing the researchers to decode a speed signal precisely from only a few neurons.
Weizmann Institute of Science researcher Nachum Ulanovsky, who investigates the neurons used by bats for navigation but is not involved in the NTNU study, explained that while weak signals have been detected in the brain, the discovery of the speed cells provide a more clear and powerful signal to study.
He compared the difference between the signals to speedometers of cars, wherein meters with a 50-mile-per-hour range provides a more accurate reading than a 40-mile-per-hour one with plus or minus error.
Ulanovsky also pointed out that most other researchers assume that the navigation system of the brain is similar across different species of mammals, but that it would be difficulty to identify the human speed cells.
The NTNU researchers said their next objective is to understand how the different types of cells function together to give an individual a sense of location and how the internal map is used to help it navigate.
The Norwegian University of Science and Technology study is published in the journal Nature.
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