A neural signature of pattern separation in the monkey hippocampus

Significance When a person experiences a stimulus similar to one held in recent memory, the brain is tasked to discriminate these overlapping representations. This process is termed pattern separation. We evoked this process in monkeys by having them serially view novel, repeat, and similar images, and could reliably predict which of these three stimuli they were viewing from electrophysiological responses of their hippocampal neurons. Neurons that best identify images fall into two stereotyped response patterns, with only one group able to distinguish similar vs. repeat images, the crucial pattern separation probe. These results show a neural signature in hippocampus indicative of pattern separation, which will contribute to our understanding of how the brain recognizes differences in the service of making memories.