Education and brain amyloid load act on temporal lobe function in individual with subjective memory complaint: An EEG‐fMRI study

Abstract

AbstractBackgroundThe cognitive reserve (CR) moderate the effect of brain pathophysiology on cognitive deficits in Alzheimer's Disease (AD) continuum. In a previous study on individuals with subjective memory complaint (SMCs), a condition at risk for AD, from the INSIGHT‐preAD cohort, we found that CR altered the association of amyloid load with neurophysiological mechanisms generating posterior electroencephalographic (EEG) alpha rhythms in quiet wakefulness. We used educational attainment (Edu) as an indicator of CR.MethodIn the present work we tested the hypothesis of the interaction of Edu and cerebral amyloid‐b load with the association between posterior alpha rhythms, as revealed by resting‐state EEG (rsEEG) activity, and functional connectivity, as revealed by functional magnetic resonance imaging (fMRI, 3‐Tesla Verio system), among cholinergic basal forebrain (BF), thalamus, and posterior cortical areas. Resting‐state EEG and fMRI data were acquired in 318 cognitively intact individuals (age between 70 and 85 years) with SMC. Participants were stratified into two groups of amyloid‐positive (SMCpos) and ‐negative (SMCneg), using the standard diagnostic markers of Alzheimer's neuropathology based on cortical‐to‐cerebellum standardized uptake value ratio in the PET imaging. Then, the education attainment level was used to stratify the SMC participants in those with a low‐to‐moderate education level (SMC Edu‐) and those with a high education level (SMC Edu+).ResultResults showed a significant positive association between temporal alpha rhythms and above‐mentioned functional connectivity in the SMC cases with low brain amyloid accumulation and education attainment (SMCneg Edu‐). In contrast, the SMCneg Edu+ seniors showed the amplest posterior alpha rhythms, but not a positive association between temporal alpha rhythms and fMRI connectivity among cholinergic BF, thalamus, and posterior cerebral cortex, possibly due to a (annulation) of high CR. Of note, the SMCpos Edu+ seniors showed this positive association, possibly due to the (neutralization) of CR and brain amyloidosis (Figure 1).ConclusionThe present results suggest that, in SMC seniors, high CR affects cortical neural synchronization mechanisms generating posterior rsEEG alpha rhythms, but not through the ascending cholinergic system to the posterior cortex. Unfortunately, these CR effects may be annulled at earlier stages of Alzheimer's amyloid pathophysiology.