Speed cells are neurons whose firing rates depend on an animal's speed through its environment. Together with

place cells A place cell is a kind of pyramidal neuron in the hippocampus that becomes active when an animal enters a particular place in its environment, which is known as the place field. Place cells are thought to act collectively as a cognitive represe ...

grid cells A grid cell is a type of neuron within the entorhinal cortex that fires at regular intervals as an animal navigates an open area, allowing it to understand its position in space by storing and integrating information about location, distance, and ...

boundary cell Boundary cells (also known as border cells or boundary vector cells) are neurons found in the hippocampal formation that respond to the presence of an environmental boundary at a particular distance and direction from an animal. The existence of cel ...

s, and

head direction cells Head direction (HD) cells are neurons found in a number of brain regions that increase their firing rates above baseline levels only when the animal's head points in a specific direction. They have been reported in rats, monkeys, mice, chinchillas a ...

, they form a part of a larger set of neurons that are involved in cognitive mapping of the surrounding environment. Speed cells are found in the

entorhinal cortex The entorhinal cortex (EC) is an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time.Integrating time from experience in the ...

Background

With the discovery of grid cells in 2005 by

Edvard Moser Edvard Ingjald Moser (; born 27 April 1962) is a Norwegian professor of psychology and neuroscience at thKavli Institute for Systems Neuroscience at the Norwegian University of Science and Technology (NTNU) in Trondheim. In 2005, he and May-Brit ...

and May Britt Moser, realized that the grid cells were not alone in deducing the spatial location of the animal. The grid cells used information about direction and speed in order to find the location. The discovery of head direction by James B. Ranck, Jr. located the cells responsible for information on direction of head or heading of animal. The Mosers kept searching for the assumed speed cells and in 2015, were able to prove the presence of such cells in the medial entorhinal cortex. The speed cells fire in response to variations in speed of the animal. It was also found that unlike place cells, the speed cells are independent of visual cues. Darkness did not influence the firing rate of the animal. Another interesting feature of the cells is that the firing of the cells is better correlated with the future speed of the animal suggesting that the speed of the animal is known in advance by the speed cells.

Experiment

In the experiment conducted by the Mosers', rats were made to run a constricted 4 meter long track. The module resembled a car from ''

The Flintstones ''The Flintstones'' is an American animated sitcom produced by Hanna-Barbera Productions. The series takes place in a romanticized Stone Age setting and follows the activities of the titular family, the Flintstones, and their next-door neighb ...

'' cartoon with no bottom. The rats were guided by this car to run at speed of 7, 14, 21 and 28 cm/s. The firing of the cells was recorded. The rat was awarded with chocolate at the end of the track. In order to eliminate the response of nearby entorhinal cells on the readings, a second experiment was conducted. In this the rats were allowed to forage freely with speed varying from 0 to 50 cm/s.

Function

The speed cell firing in response to the movement of the animal provides instantaneous running speed to the

grid cell A grid cell is a type of neuron within the entorhinal cortex that fires at regular intervals as an animal navigates an open area, allowing it to understand its position in space by storing and integrating information about location, distance, and ...

. The grid cell in turn uses this information along with the head direction in order to calculate the location of the animal in the cognitive map. The grid cell along with

border cells The border cells are a cluster of 6-8 cells that migrate in the ovariole of the fruit-fly ''Drosophila melanogaster,'' during the process of oogenesis. A fly ovary consists of a string of ovarioles or egg chambers arranged in an increasing order ...

, speed cells and

provide a correlation between different movement aspects of the animal with respect to its environment. Alzheimer's disease involves damage to the entorhinal cortex. This area contains most of the cells involved in cognitive mapping and this could suggest why patients suffering from Alzheimer's disease tend to forget or become lost. Edvard Moser also suggests that understanding the working of the human GPS can provide cues to understanding other brain functions such as association of smell and memory.

References

{{Reflist, 1 Neurons Neuroanatomy