Global functional coupling of resting EEG rhythms is related to white-matter lesions along the cholinergic tracts in subjects with amnesic mild cognitive impairment

We tested the hypothesis that global functional coupling of resting cortical electroencephalographic (EEG) rhythms is abnormal in amnesic mild cognitive impairment (MCI) patients with remarkable lesions along the cholinergic white-matter tracts. We used the eyes-closed resting EEG data (10-20 montage) of the same groups of 28 healthy elderly (Nold) and 57 MCI subjects of a previous reference study. The estimation of the cholinergic lesion was performed with a validated semi-automatic algorithm based on fluid-attenuated inversion recovery sequences on MRI. The MCI patients were divided into groups of high (MCI+; n=28) and low (MCI-; n=29) cholinergic damage. EEG rhythms of interest were delta (2-4 Hz), theta (4-8 Hz), alpha1 (8-10.5 Hz), alpha2 (10.5-13 Hz), beta1 (13-20 Hz), beta2 (20-30 Hz), and gamma (30- 40 Hz). The global functional coupling of the EEG rhythms was indexed computing the spectral coherence between each electrode and the other 18 electrodes ("electrode" coherence) and then averaging the "electrode" coherence of all 19 electrodes (total coherence). Total coherence of alpha1 rhythms was highest in the Nold, intermediate in the MCI-, and lowest in the MCI+ groups. Furthermore, the alpha1 total coherence was negatively correlated to (moderate to high) cholinergic lesion across the MCI subjects. In conclusion, damage to the cholinergic system is associated with alterations of the functional global coupling of resting alpha rhythms.