Imagine you’re driving a car down a long road, and suddenly you notice that the steering wheel feels a little off and the car doesn’t respond as quickly. It’s a small change, but it’s enough to make you question if something is wrong with your vehicle. This is similar to what scientists are studying with subjective cognitive decline (SCD), which appears in the early stages of Alzheimer’s disease. In this study, researchers used resting-state functional MRI to examine the dynamic connectivity of the brains in people with SCD compared to cognitively normal individuals. They discovered that the local dynamics of brain activity were altered in regions responsible for executive control and attention. Interestingly, they also found compensatory increases in visual processing and bottom-up attention. These findings suggest that SCD is a transitional stage between normal cognition and dementia, and that the brain engages in complex compensatory mechanisms to maintain cognitive function. To learn more about how the brain changes during SCD, check out the full article!

BackgroundSubjective cognitive decline (SCD) appears in the preclinical stage of the Alzheimer’s disease continuum. In this stage, dynamic features are more sensitive than static features to reflect early subtle changes in functional brain connectivity. Therefore, we studied local and extended dynamic connectivity of the resting brain of people with SCD to determine their intrinsic brain changes.MethodsWe enrolled cognitively normal older adults from the communities and divided them into SCD and normal control (NC) groups. We used mean dynamic amplitude of low-frequency fluctuation (mdALFF) to evaluate region of interest (ROI)-wise local dynamic connectivity of resting-state functional MRI. The dynamic functional connectivity (dFC) between ROIs was tested by whole-brain-based statistics.ResultsWhen comparing SCD (N = 40) with NC (N = 45), mdALFFmean decreased at right inferior parietal lobule (IPL) of the frontoparietal network (FPN). Still, it increased at the right middle temporal gyrus (MTG) of the ventral attention network (VAN) and right calcarine of the visual network (VIS). Also, the mdALFFvar (variance) increased at the left superior temporal gyrus of AUD, right MTG of VAN, right globus pallidum of the cingulo-opercular network (CON), and right lingual gyrus of VIS. Furthermore, mdALFFmean at right IPL of FPN are correlated negatively with subjective complaints and positively with objective cognitive performance. In the dFC seeded from the ROIs with local mdALFF group differences, SCD showed a generally lower dFCmean and higher dFCvar (variance) to other regions of the brain. These weakened and unstable functional connectivity appeared among FPN, CON, the default mode network, and the salience network, the large-scale networks of the triple network model for organizing neural resource allocations.ConclusionThe local dynamic connectivity of SCD decreased in brain regions of cognitive executive control. Meanwhile, compensatory visual efforts and bottom-up attention rose. Mixed decrease and compensatory increase of dynamics of intrinsic brain activity suggest the transitional nature of SCD. The FPN local dynamics balance subjective and objective cognition and maintain cognitive preservation in preclinical dementia. Aberrant triple network model features the dFC alternations of SCD. Finally, the right lateralization phenomenon emerged early in the dementia continuum and affected local dynamic connectivity.

Read Full Article (External Site)