Fluid intelligence and its neural correlates in early onset mild cognitive impairment

Abstract

AbstractBackgroundFluid intelligence refers to the ability of abstract reasoning, problem‐solving and other mental activities considered to be independent from learned knowledges and experience. It has been demonstrated that fluid intelligence is compromised in Mild Cognitive Impairment (MCI), but it also declines with ageing. We tested if fluid intelligence is also affected when MCI occurs before 65 years of age (i.e., in early‐onset MCI) and studied its specific functional and structural brain correlates independently from the effect of ageing.MethodEighty‐five subjects with early‐onset MCI (cognitive symptoms onset < 65 years) underwent extended neuropsychological assessment including Raven’s Coloured Progressive Matrices (RCPM), a culture‐free non‐verbal relational reasoning task that is considered a proxy of fluid intelligence. They also underwent multimodal Magnetic Resonance Imaging (MRI) protocol on a 3T scanner including high‐resolution T1 and sequences acquired at rest for functional MRI (fMRI). Performance at RCPM was related to regional grey matter volume using Voxel Based Morphometry (VBM) and to functional connectivity of resting‐state networks (RSNs) known to be related to cognition using independent component analysis.ResultsThe median RCPM score was 27 (range 8‐36, with 36 being the maximum obtainable score). Among all 85 patients, only 11.8% (N=10) performed below the age and education‐corrected cut‐off. These patients also had significantly lower scores in almost all the remaining neuropsychological tests, suggesting that they were in a more severe stage of MCI (i.e., close to conversion). VBM results showed that, across all patients, decreased performance on RCPM was associated with focal atrophy in right fronto‐temporal and bilateral parietal areas (Figure 1). FMRI acquired at rest showed that better performance on RCPM was associated with lower functional connectivity in areas of the anterior DMN and with higher functional connectivity in areas of the left fronto‐parietal RSN (also indicated as the working memory RSN).ConclusionIn patients with early‐onset MCI fluid intelligence is relatively preserved, associated with lower atrophy in right fronto‐temporal and bilateral parietal regions, and with decreased functional connectivity in the anterior DMN and increased in the left fronto‐parietal network.