Pilot investigation of the relationship between hippocampal volume and pattern separation deficits in multiple sclerosis.

Memory impairment and hippocampal atrophy are common in multiple sclerosis (MS). In the present pilot study, we investigate whether the mnemonic process of pattern separation is impaired and a predictor of hippocampal volume in relapsing remitting MS. MS participants and healthy controls completed the Mnemonic Similarities Task (MST) along with traditional neurocognitive assessments of memory. 3T structural magnetic resonance imaging was used to estimate whole hippocampal volumes (main aim) and hippocampal subfield volumes (exploratory aim). Results revealed that pattern separation performance was worse for MS participants compared to healthy controls (Cohen's d = 0.96). For MS participants, hippocampal volume was more strongly related to pattern separation performance (r = 0.83) than a traditional neurocognitive measure of visual memory (r = 0.65); hippocampal volume was not related to a traditional neurocognitive measure of verbal memory in this sample. No brain-behavior correlations were significant in the healthy control group. Results of the exploratory analysis revealed relationships between pattern separation performance and subiculum, molecular layer, and CA1 hippocampal subfield volumes for MS participants only. Pattern separation assessed using the MST may be a sensitive cognitive-biomarker of memory dysfunction and changes in hippocampal volume in relapsing-remitting MS.