Altered resting state functional connectivity of the hippocampus and thalamus in amnestic mild cognitive impairment: an fMRI study

Alzheimer’s disease (AD) is sometimes preceded by a stage known as amnestic mild cognitive impairment (aMCI), which is characterised by memory deficits abnormal for age in the absence of dementia. Although not in itself a diagnostic entity, because individuals with aMCI are at a greatly increased risk of developing AD there is an interest in characterising brain changes associated with the syndrome as compared to healthy ageing. In the current study we investigated the resting state functional connectivity (FC) of two important subcortical brain structures, the hippocampus and thalamus using functional magnetic resonance imaging (fMRI) in a group of 15 aMCI subjects and 16 healthy controls (HC). The groups were matched for age, gender and education level. Compared to the HC, the aMCI group showed significantly reduced FC of the hippocampus and thalamus to a number of brain regions (p < 0.05 corrected in all cases), particularly in the frontal and parietal cortex. FC was reduced between both right and left thalamus and bilateral supramarginal gyrus and inferior frontal gyrus (IFG) and left cerebellum; and between both right and left hippocampus and areas of frontal, temporal and parietal cortex. This study is being conducted as part of a wider project which incorporates diffusion imaging tractography of limbic white matter pathways. In the same cohort there was found to be almost no difference in white matter indices of the fornix, which directly connects the hippocampus and thalamus, suggesting that FC may be an earlier biomarker for connectivity changes in aMCI.