The hippocampus is the part of the limbic system of the brain that have been studied over the years by researchers in relation to how the brain processes and stores memory. One of the major functions of the hippocampus is the processing and retrieval of declarative memories such as facts and events, also in spatial relationship memories.The hippocampus also helps in the transferring of new short-term memories into long-term memories.
Any damage to the hippocampus would most likely lead to memory impairment. The surgery Santiago underwent to control his epilepsy is most likely to have resulted in the damage of the hippocampus in his brain, which makes him unable to form new memories of his experiences.