EEG synchronization in mild cognitive impairment and Alzheimer's disease

Objectives - To compute the synchronization likelihood of multichannel electroencephalogram (EEG) data in Alzheimer (AD) patients, subjects with mild cognitive impairment (MCI) and subjects with subjective memory complaints (SC). Material and methods - EEGs (200 Hz sample frequency; 21 channels; average reference) were recorded in 10 AD patients (two males; age 76.2; SD 9.36; range 59-86), 17 subjects with MCI (eight males; age 77.41; SD 6.25; range 62-88) and 20 subjects with SCI (11 males; age 68.9; SD 12.96; range: 51-89). The synchronization likelihood, a novel type of coherence measure, was computed, comparing each channel with all other channels, for the 2-6, 6-10, 10-14, 14-18, 18-22 and 22-50 Hz band. Results - The synchronization likelihood was significantly decreased in the 14-18 and 18-22 Hz band in AD patients compared with both MCI subjects and healthy controls. Lower beta band synchronization correlated with lower Mini-Mental state examination (MMSE) scores. Conclusion - Loss of beta band synchronization occurs early in mildly affected AD patients and correlates with cognitive impairment.