Background: There is extensive evidence for volumetric reductions in the hippocampus in patients with anorexia nervosa (AN), however the impact on function is unclear. Pattern separation and recognition are hippocampus-dependent forms of learning thought to underlie stimulus discrimination.
Methods: The present study used the Mnemonic Similarity Task to investigate pattern separation and recognition for the first time in patients with AN (N = 46) and healthy controls (N = 56). An Analysis of Covariance examined between-group differences, controlling for age, antidepressant use and method of task delivery (remote vs. in person).
Results: When controlling for covariates, pattern recognition memory scores were lower in the AN group with a medium effect size (d = 0.51). In contrast, there was a small effect whereby patients with AN had a greater pattern separation score than controls (d = 0.34), albeit this difference was not significant at the p = 0.05 threshold (p = 0.133). Furthermore, pattern separation and recognition memory abilities were not related to age, body mass index, eating disorder psychopathology or trait anxiety levels.
Conclusions: This preliminary study provides initial evidence for an imbalance in pattern separation and recognition abilities in AN, a hippocampus-dependent cognitive ability. Further studies should endeavour to investigate pattern separation and recognition performance further in AN, as well as investigate other hippocampus-dependent functions.
Keywords: Anorexia nervosa; Hippocampus; Mnemonic similarity task; Pattern separation; Recognition memory.
The hippocampus is an area of the brain that is vital for memory and learning, and it is not understood the extent to which its function is impaired in anorexia nervosa (AN). This paper used the Mnemonic Similarity Task to assess pattern separation, a hippocampus-dependent form of memory, in AN. This task involves showing participants a sequence of objects, who then categorise them as “indoor” or “outdoor” objects. Participants are later shown a sequence of objects, although some of the images are replaced by a similar but slightly different image. The task involves recognising whether an image has previously been seen (pattern recognition) and also whether it is similar to, but distinct, from a previous image (i.e. pattern separation). In this study, individuals with AN showed reduced performance in pattern recognition, when statistically controlling for their age, how the task was delivered and their use of antidepressant medication. However, their performance in pattern separation was intact. This may indicate an imbalance in this hippocampus-dependent form of memory in AN.