Synchronization during an internally directed cognitive state in healthy aging and mild cognitive impairment: a MEG study

Abstract

Mild Cognitive Impairment (MCI) is a stage between healthy aging and dementia. Functional connectivity is widely used to study the brain activity during resting state or cognitive tasks. We aimed to determine the functional connectivity changes required to deal with an Internally Directed Cognitive State (IDICS) in healthy aging and MCI. This task differs from the most commonly employed in Magnetoencephalograpy (MEG)/ Electroencephalography (EEG), since inhibition from external stimuli is needed, and it allows the study of this control mechanism in healthy and pathological aging. To this end, MEG signals were acquired from 32 healthy individuals and 38 MCI patients, both in resting state and while performing a subtraction task of two levels of difficulty. Phase Locking Value (PLV) was calculated for five frequency bands: delta, theta, alpha, beta and gamma. Synchronization patterns changed in both groups while performing the task. MCI patients presented higher connectivity changes than those in the control group, and this was related to a lower cognitive performance. In particular, in MCIs a hypersynchronization in delta, theta, beta and gamma bands was found, which reveals an abnormal functioning in this group. Contrary to controls, MCIs presented a lack of synchronization in the alpha band which may denote an inhibition deficit. Additionally, the magnitude of connectivity changes rose with the task difficulty in controls but not in MCIs, in line with the CRUNCH model (Compensation-Related Utilization of Neural Circuits Hypothesis).