Cortical sources of resting EEG rhythms in mild cognitive impairment and subjective memory complaint

Are cortical electroencephalographic (EEG) rhythms altered in amnesic and non-amnesic mild cognitive impairment (MCI), subjective memory complaint (SMC), and healthy elderly (Nold) subjects? Eyes-closed resting EEG was recorded in 79 Nold, 53 SMC, 51 non-amnesic MCI, and 92 amnesic MCI subjects. EEG rhythms of interest were delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13 Hz), beta 1 (13-20 Hz), beta 2 (20-30 Hz) and gamma (30-40 Hz). Cortical EEG sources were estimated by standardized low resolution brain electromagnetic tomography (sLORETA). Results showed that (i) the frontal delta sources were greater in amplitude in the amnesic MCI and SMC subjects than in the Nold subjects (p<0.05-0.01); (ii) the parietal and occipital theta sources were lower in amplitude in the SMC subjects than in the Nold subjects (p<0.046); (iii) the occipital theta sources were greater in amplitude in the amnesic MCI subjects than in the SMC and non-amnesic MCI subjects (p<0.02-0.01); (iv) the parietal and occipital alpha 1 sources were greater in amplitude in the Nold subjects than in the SMC, non-amnesic MCI and amnesic MCI subjects (p<0.00001); (v) the central alpha 1 sources were lower in amplitude in the SMC subjects than in the non-amnesic MCI subjects (p<0.002); (vi) the occipital alpha 1 sources were greater in amplitude in the SMC subjects than in the amnesic MCI subjects (p<0.0003); (vii) the parietal and occipital alpha 2 sources were greater in amplitude in the Nold subjects than in the non-amnesic MCI subjects (p<0.041-0.0004); (viii) the occipital alpha 2 sources were greater in the SMC subjects than in the non-amnesic MCI subjects (p<0.02). These results suggest that amnesic MCI and SMC subjects present some of the typical alterations of brain neural synchronization as revealed by resting cortical EEG rhythms in Alzheimer's disease patients.