Let me explain why the hippocampus was thought to be important for memory. In 1953, a person removed the surroundings of the hippocampus by surgery, and after the surgery he could not remember anything. The other surgery to remove other parts of the brain does not hinder the memory. By this discovery, it is thought that the hippocampus plays an important role in memory.

Interestingly, he could do conversation and daily life with no problem. In addition, he remembered childhood memory, and also he was able to remember things temporarily for a short period of time. He cannot create new memories that last more than a few days.

By those discoveries, the hippocampus attracts the attention of researchers. 

*4 He had epilepsy. The hippocampus is thought to be the source of his epilepsy. It was thought that if surgically remove the part, his epilepsy would cure.