Validation of the Mnemonic Similarity Task - Context Version

Objective: Pattern separation (PS) is the ability to represent similar experiences as separate, non-overlapping representations. It is usually assessed via the Mnemonic Similarity Task - Object Version (MST-O) which, however, assesses PS performance without taking behavioral context discrimination into account, since it is based on pictures of everyday simple objects on a white background. We here present a validation study for a new task, the Mnemonic Similarity Task - Context Version (MST-C), which is designed to measure PS while taking behavioral context discrimination into account by using real-life context photographs. Methods: Fifty healthy subjects underwent the two MST tasks to assess convergent evidence. Instruments assessing memory and attention were also administered to study discriminant evidence. The test-retest reliability of MST-C was analyzed. Results: Weak evidence supports convergent validity between the MST-C task and the MST-O as measures of PS (rs = 0.464; p < 0.01); PS performance assessed via the MST-C did not correlate with memory or attention; a moderate test-retest reliability was found (rs = 0.595; p < 0.01). Conclusion: The MST-C seems useful for assessing PS performance conceptualized as the ability to discriminate complex and realistic spatial contexts. Future studies are welcome to evaluate the validity of the MST-C task as a measure of PS in clinical populations.

Disambiguation of Similar Object-Place Paired Associations and the Roles of the Brain Structures in the Medial Temporal Lobe

Amnesic patients who have damage in the hippocampus and in associated areas in the medial temporal lobe suffer from remembering specific events that may or may not share similar objects and locations. Computational models, behavioral studies, and physiological findings all suggest that neural circuits in the hippocampus are suitable for representing seemingly similar events as distinctively different individual event memories. This article offers a selective review on this particular function of the hippocampus and its associates areas such as the perirhinal cortex, mostly centering upon lesion studies and physiological studies using animals. We also present recent experimental results showing that the dentate gyrus subfield of the hippocampus and perirhinal cortex are particularly important for discriminating similar paired associates between same objects and different locations, or vice versa.