Place Cells
Introduction
Place cells are a type of pyramidal neuron within the hippocampus that become active when an animal enters a particular place in its environment, which is known as the cell's "place field". These cells were discovered by John O'Keefe and Jonathan Dostrovsky in 1971 and their discovery has significantly contributed to our understanding of spatial learning and navigation in mammals.
Discovery
In 1971, John O'Keefe and Jonathan Dostrovsky discovered place cells while studying the hippocampus of rats. They observed that specific neurons in the hippocampus would fire when the rat was in a particular location in the environment. This discovery was a significant breakthrough in the field of neuroscience as it provided the first evidence of a neural representation of spatial environment in the brain.
Location in the Brain
Place cells are located in the hippocampus, a region of the brain that is crucial for memory and navigation. Within the hippocampus, place cells are primarily found in the CA1 and CA3 regions, as well as the subiculum. These regions are part of the hippocampal formation, which is involved in the formation of new memories and spatial navigation.
Function
The primary function of place cells is to provide a spatial map of the environment. Each place cell has a specific place field, which is the area of the environment where the cell fires. The size and shape of the place field can vary depending on the complexity of the environment and the specific location of the cell within the hippocampus. When an animal moves through its environment, different place cells fire in sequence, creating a unique pattern of activity that represents the animal's path through space.
Properties of Place Cells
Place cells exhibit several unique properties that distinguish them from other types of neurons. These properties include:
- Place-specific firing: Place cells only fire when the animal is in the cell's place field. The firing rate increases as the animal approaches the center of the place field and decreases as it moves away.
- Directionality: Some place cells show a preference for specific directions of movement. These cells will only fire when the animal is moving in a particular direction through the place field.
- Remapping: When the animal's environment changes, place cells can "remap" their place fields. This means that the cells form new representations of the environment, allowing the animal to adapt to changes in its surroundings.
- Phase precession: As an animal moves through a place field, the place cell fires at progressively earlier phases of the animal's theta rhythm. This phenomenon, known as phase precession, is thought to play a role in the temporal coding of spatial information.
Place cells play a crucial role in spatial memory and navigation. The firing patterns of place cells create a neural map of the environment, which the animal uses to navigate and remember locations. This map is dynamic and can be updated as the animal explores new environments or as existing environments change.
Research has shown that damage to the hippocampus, and thus to place cells, can impair an animal's ability to navigate and remember locations. This has been demonstrated in studies of rats with hippocampal lesions, who show deficits in tasks that require spatial memory, such as the Morris water maze task.
Clinical Significance
Understanding the function of place cells has important implications for the study of human diseases that affect memory and spatial navigation. For example, in Alzheimer's disease, one of the earliest symptoms is often difficulty with spatial navigation, which may be due to dysfunction of place cells in the hippocampus. Research on place cells may therefore contribute to the development of new treatments for Alzheimer's disease and other memory disorders.