No one knows what causes Alzheimer’s disease. The entire hippocampus wasn’t affected, though, just a smaller subfield responsible for retrieving memories, reconstructing memories from partial information, and distinguishing between similar experiences. BRAIN CHANGES: Atrophy in a specific part of the hippocampus has been observed in both adults with depression and adults with Alzheimer’s disease. “This study shows why it’s important to look beyond the total size of the hippocampus,” study co-author Meredith N. Braskie said in a statement. “Depression wasn’t related to smaller volume throughout the entire region.