Hippocampus is a complex brain structure embedded deep into temporal lobe. It has a major role in learning and memory. It is a plastic and vulnerable structure that gets damaged by a variety of stimuli. Studies have shown that it also gets affected in a variety of neurological and psychiatric disorders. The hippocampus reports any discrepancies or problems (e.g. I see a lion at my door) to the amygdala, which sends and receives information from every part of the brain and body.
