Tuesday, May 19, 2009

The hippocampus is an elevation of the floor of each lateral ventricle of the cerebrum which consists mainly of gray matter and is covered by a layer of white matter. It is part of the lymbic system and has a central role in memory processes.

The hippocampus can be divided into two main parts: the Ammon's horn, and the dentate gyrus. The hippocampus is closely related to the cerebral cortex, and is located in the medial temporal lobe, underneath the cortical surface. It is shaped like a curved tube, which in humans is convoluted in a way that reminded early anatomists of a seahorse ("hippocampus" means "seahorse" in Greek).

Neuroscientists agree that the hippocampus plays an important role in the formation of new memories about experienced events. Some researchers view the hippocampus as part of a larger medial temporal lobe memory system responsible for long term memory. Severe damage to the hippocampus results in profound difficulties in forming new memories (anterograde amnesia), and often also affects memories formed prior to the damage (retrograde amnesia). Although the retrograde effect normally extends some years prior to the brain damage, in some cases older memories remain. This sparing of older memories leads to the idea that consolidation over time involves the transfer of memories out of the hippocampus to other parts of the brain. Damage to the hippocampus does not affect some types of memory, such as the ability to learn new motor or cognitive skills.