The hippocampus is located in the medial temporal lobe of the brain, below the cortical surface. Its structure is divided into two halves that are found on the left and right sides of the brain. The organ is curved into a shape that resembles a seahorse, and its name is derived from a coupling of the Greek words "hippo" for the horse and "kampos" for the sea.
The hippocampus was first referred to by the Venetian anatomist Julio César Aranzi in 1587. He described it as a ridge along the floor of the temporal horn of the lateral ventricle and compared it first to a silkworm and later to a sea horse. In the 1740s, a Parisian surgeon René-Jacques Croissant de Garengeot coined the term "cornu Ammonis", which means the horn of Amun, an ancient Egyptian god.
The hippocampus takes care of long-term memory formation and space navigation. In diseases such as Alzheimer's disease, the hippocampus is one of the first regions of the brain to be damaged and this leads to the memory loss and disorientation associated with the condition.
The hippocampus can become damaged through oxygen deprivation or hypoxia, infection or inflammation, or as a result of temporal lobe epilepsy. Individuals with hippocampal damage develop amnesia and may be unable to form new memories of the time or location of an event, for example.
In Alzheimer's disease (and other forms of dementia), the hippocampus is one of the first regions of the brain to suffer damage; Short-term memory loss and disorientation are among the first symptoms. Damage to the hippocampus can also be due to oxygen starvation (hypoxia), encephalitis, or medial temporal lobe epilepsy. People with extensive bilateral hippocampal damage may experience anterograde amnesia (the inability to form and retain new memories).
Since the different types of neuronal cells are neatly layered in the hippocampus, it has been frequently used as a model system for the study of neurophysiology. The form of neural plasticity known as long-term potentiation (LTP) was first discovered in the hippocampus and has often been studied in this structure. LTP is widely believed to be one of the main neural mechanisms by which memories are stored in the brain.
