Pattern separation deficits following damage to the hippocampus

Computational models of hippocampal function propose that the hippocampus is capable of rapidly storing distinct representations through a process known as pattern separation. This prediction is supported by electrophysiological data from rodents and neuroimaging data from humans. Here, we test the prediction that damage to the hippocampus would result in pattern separation deficits by having memory-impaired patients with bilateral hippocampal damage study a series of objects or faces and then perform a modified recognition memory test. In the test phase, participants viewed true repetitions, novel foils, and lures that were perceptually and semantically related to the studied stimuli. Patients with hippocampal damage were unimpaired relative to matched controls in their baseline recognition memory. However, patients were less likely to uniquely identify lures as “similar” than matched controls, indicating an impairment in pattern separation processes following damage to the hippocampus.

► Memory-impaired patients and control participants.
► Patients had intact recognition memory for objects and faces.
► Patients had impaired pattern separation performance.