We are all familiar with this situation – at a party, we are introduced to the other guests, but we only remember two or three names. For our brain, the rest is all hollow words. The region of our brain which decides over remembering and forgetting is called hippocampus (Greek: seahorse), because its shape is reminiscent of a seahorse.

Some scientists have likened the hippocampus to the "record" button on a VCR. The brain receives hundreds of sensory impressions every second. For a short time, the hippocampus stores all these new sensations. Most of these impressions are fleeting and quickly forgotten. However, during a time of joy, triumph, tragedy or danger, the hippocampus senses our elevated emotional level and essentially presses the "record" button. This causes the incoming impressions and informationto be taken over into the long-term memory or not.
Because of this function of the hippocampus a highly emotional scene from a movie can stay with us for years. We can easily record details from long past events, e.g. our wedding day, the birth of a child, or the death of a parent, however, often we can't remember where we have left the car key.

People whose hippocampus is damaged, have severe memory problems. They live in the past.
In the late fifties, surgeons removed parts of the hippocampus of a 20-year-old patient to treat his severe epilepsy which could not be controlled by drugs. From then on, the man was no longer able to store new memories. The patient believed that he was still 20 years old, and he could not remember people whom he had met since. In the seventies, when he was shown pictures of astronauts on the moon, the patient believed that this was a scene from a movie. However, the patient could remember experiences from childhood and adolescence well, even up to about two years prior to the surgery.

The hippocampus and the associated brain areas adjacent to the hippocampus are the first regions that begin to develop insoluble clumps in Alzheimer's disease, which results in the death of important nerve cells. This is the reason for the memory problems observed in Alzheimer's patients.