Memory pathologies

The neuroanatomy of memory encompasses a wide variety of anatomical structures in the brain.

The hippocampus is a structure in the brain that has been associated with various memory functions. It is part of the limbic system, and lies next to the medial temporal lobe. It is made up of two structures, the Ammon's Horn, and the Dentate gyrus, each containing different types of cells.

There is evidence that the hippocampus contains cognitive maps in humans. In one study, single-cell recordings were taken from electrodes implanted in a rat's hippocampus, and it was found that certain neurons responded strongly only when the rat was in certain locations. These cells are called place cells, and collections of these cells can be considered to be mental maps. Individual place cells do not only respond to one unique area only however, the patterns of activation of these cells overlap to form layered mental maps within the hippocampus. A good analogy is the example of the same television or computer screen pixels being used to light up any trillions of possible combinations to produce images, just as the place cells can be used in any multiple possible combinations to represent mental maps. The hippocampus' right side is more oriented towards responding to spatial aspects, whereas the left side is associated with other context information. Also, there is evidence that experience in building extensive mental maps, such as driving a city taxi for a long time (since this requires considerable memorization of routes), can increase the volume of one's hippocampus.

Damage to the hippocampus and surrounding area can cause anterograde amnesia, the inability to form new memories. This implies that the hippocampus is important not only for storing cognitive maps, but for encoding memories.

The hippocampus is also involved in memory consolidation, the slow process by which memories are converted from short to long term memory. This is supported by studies in which lesions are applied to rat hippocampi at different times after learning. The process of consolidation may take up to a couple years.

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