Place cells

A place cell is a type of pyramidal neuron within the hippocampus that becomes active when an animal enters a particular place in its environment; this place is known as the place field. A given place cell will have only one, or a few, place fields in a typical small laboratory environment, but more in a larger region. There is no apparent topography to the pattern of place fields, unlike other brain areas such as visual cortex—neighboring place cells are as likely to have nearby fields as distant ones. In a different environment, typically about half the place cells will still have place fields, but these will be in new places unrelated to their former locations.

Place cells are thought, collectively, to act as a cognitive representation of a specific location in space, known as a cognitive map. Place cells work with other types of neurons in the hippocampus and surrounding regions to perform this kind of spatial processing, but the ways in which they function within the hippocampus are still being researched.

Studies with rats have shown that place cells tend to fire quickly when a rat enters a new, open environment, but outside of a firing field, place cells tend to be relatively inactive. Together place cells are thought to form a "cognitive map" in which they have localized firing patterns called place fields. Place cell firing patterns are often determined by external sensory information and the local environment. Place cells have proven to have the ability to suddenly change their firing pattern from one pattern to another, a phenomenon known as "re-mapping" and though place cells do change according to the external environment, they are stabilized by attractor dynamics which "enable the system to resist small changes in sensory input but respond collectively and coherently to large ones."

Although place cells are part of a non-sensory cortical system, their firing behavior is strongly correlated to sensory input. Place cells fire when an animal is located in parts of the environment known as place fields. These circuits may have important implications for memory, as they provide the spatial context for memories and past experiences. Like many other parts of the brain, place cell circuits are dynamic. They are constantly adjusting and remapping to suit the current location and experience of the brain. Place cells do not work alone to create visuospatial representation; they are a part of a complex circuit that informs place awareness and place memory.

The 2014 Nobel Prize in Physiology or Medicine was awarded to John O'Keefe for the discovery of place cells, and to Edvard and May-Britt Moser for the discovery of grid cells.

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