Mnemonic Similarity Task: A Tool for Assessing Hippocampal Integrity

Abstract

The hippocampus is critical for learning and memory, relying in part on pattern separation processes supported by the dentate gyrus (DG) to prevent interference from overlapping memory representations. In 2007, we designed the Mnemonic Similarity Task (MST), a modified object recognition memory task, to be highly sensitive to hippocampal function by placing strong demands on pattern separation. The MST is now a widely used behavioral task, repeatedly shown to be sensitive to age-related memory decline, hippocampal connectivity, and hippocampal function, with specificity to the DG. Here, we review the utility of the MST, its relationship to hippocampal function, its utility in detecting hippocampal-based memory alterations across the lifespan, and impairments associated with clinical pathology from a variety of disorders.

Keywords: discrimination; hippocampus; mnemonic similarity; pattern separation.

Figure 1.. Mnemonic Similarity Task.

A) Examples of stimuli during the incidental encoding and subsequent Old/Similar/New recognition task. Colored boxes are to illustrate conditions, but not used during the actual task administration. B) Examples of images for each of the lure bins, ranging from most similar (lure bin 1) to least similar (lure bin 5).

Figure 2.. Old, Similar, and New responses for Targets, Lures, and New Foil items.

In young (A; 20-39), older (B; 60-74) and MCI (C) participants, LDI declines with age and MCI (D), while REC remains stable in healthy aging (E). Older adults who are impaired relative to young adults and those with MCI show different trajectories in discriminating lures across similarity bins (F).