The decline of verbal memory after stroke is associated with decreased functional connectivity of hippocampal subregions

Background The hippocampus plays an important role in learning and integrating events to form episodic memory. Many ischemic stroke survivors experience memory impairments, and some report decline in memory function. We examined changes in functional connectivity (FC) of the hippocampus and its subregions in stroke survivors over 3 years compared to age‐matched stroke‐free healthy controls (HC), and the associations between hippocampal FC and verbal memory performance. Method Participants from the Cognition And Neocortical Volume After Stroke Study were analysed at 3‐months, 1‐year and 3‐years post‐stroke. Verbal memory performance at each timepoint was evaluated with delayed recall of the Hopkins Verbal Learning Test‐Revised that was standardized using appropriate age stratified normative data. Evaluable resting‐state functional magnetic resonance imaging sequences were compared with age‐matched healthy controls (see Table 1 for demographics) following pre‐processing. The hippocampus was parcellated into whole hippocampus and four subregions (body, head‐medial, head‐lateral and tail) and bilateral seed‐based FC analyses were conducted for each region using CONN toolbox (V20.b). Longitudinal changes of FC between two timepoints were computed by the direct subtraction. Result Groups were age‐ and sex‐matched but HC had significantly greater years of education (see Table 1). Greater FC change was seen in stroke survivors between 3‐months to 1‐year in left hippocampal head‐medial (right lateral occipital; p‐FDR = 0.012) with years of education adjusted. Stroke patients displayed significant decline in verbal memory between the 1‐ and 3‐year timepoints. Significantly decreased FC of left hippocampal head‐medial (precuneus; p‐FDR = 0.011) correlated with verbal memory decline between 3‐months and 3 years after adjusting years of education and gender. There was no significant decline or change of verbal memory observed in HC, and the correlated hippocampal FC changes were not present in HC group either. Conclusion Change in left hippocampal subregional FC is different in stroke survivors compared to HC. Subregional hippocampal FC changes correlate with verbal memory decline. Subfield FC analyses may shed new light into mechanisms of post‐stroke memory impairment.