The Human Dentate Gyrus Plays A Necessary Role in Discriminating New Memories

Episodic memory provides us with the ability to re-experience unique events in rich detail. For this to occur, we must be able to 1) behaviorally pattern separate or discriminate new from old experiences, and 2) pattern complete or reinstate memories from partial cues. I report a rare individual with a specific lesion to the dentate gyrus of his hippocampus who has difficulty distinguishing between studied targets and unstudied lures that are visually similar. In addition, he displays a heightened tendency to recognize studied scenes from degraded pictures. These results provide the first direct evidence in humans that discriminating new memories cannot wholly function without an intact dentate gyrus and that this mnemonic ability is dissociable from, but likely interacts with, completion processes in the CA3 subfield of the hippocampus.