Mnemonic Discrimination in Obsessive Compulsive Disorder Patients: A Case-Control Study

Background: Fear generalization is an adaptive mechanism which enables an individual to appropriately respond to novel stimuli based on overlapping features with a learned threat stimulus. When it is maladaptive, it is named overgeneralization. Overgeneralization was observed in psychiatric disorders, including Obsessive-Compulsive Disorder (OCD). Overgeneralization seems to be related to mnemonic discrimination, a fundamental component of memory which encodes a given event as distinct from highly similar events. Mnemonic discrimination is thought to rely on Pattern Separation (PS), which plays a critical role in discriminating safe stimuli similar to threatening ones. PS performance showed to be impaired in patients with some psychiatric disorders but has never been studied in OCD. Objective: Mnemonic discrimination for context, used as a proxy of pattern separation, was measured in patients with OCD to verify whether it is related to over-generalization. Methods: Thirty patients with OCD and 30 non-psychiatric controls were enrolled (matched for sex, age). The Mnemonic Similarity Task-Object and the Mnemonic Similarity Task-Contest were administered to assess PS performance. Results: When patients with OCD and controls were compared, statistically significant differences were not found for mnemonic performances and pattern separation. Based on multivariate regression analysis, the group of patients with OCD was more likely to report lower mnemonic discrimination for context (OR = 0.67, 95% CI = 0.48-0.93) than the control group. Conclusion: Mnemonic discrimination for context was specifically referred to as new lures misidentified as similar. It is hypothesized that pattern separation performances might discriminate patients with OCD from non-psychiatric subjects.