Fronto-parietal coupling of brain rhythms in mild cognitive impairment. A multicentric EEG study.

Electroencephalographic (EEG) data were recorded in 69 normal elderly (Nold), 88 mild cognitive impairment (MCI), and 109 mild Alzheimer’s
disease (AD) subjects at rest condition, to test whether the fronto-parietal coupling of EEG rhythms is in line with the hypothesis that MCI can
be considered as a pre-clinical stage of the disease at group level. Functional coupling was estimated by synchronization likelihood of Laplaciantransformed
EEG data at electrode pairs, which accounts for linear and non-linear components of that coupling. Cortical 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). Compared
to the Nold subjects, the AD patients presented a marked reduction of the synchronization likelihood (delta to gamma) at both fronto-parietal and
inter-hemispherical (delta to beta 2) electrodes. As a main result, alpha 1 synchronization likelihood progressively decreased across Nold, MCI, and
mildADsubjects at midline (Fz–Pz) and right (F4–P4) fronto-parietal electrodes. The samewas true for the delta synchronization likelihood at right
fronto-parietal electrodes (F4–P4). For these EEG bands, the synchronization likelihood correlated with global cognitive status as measured by the
Mini Mental State Evaluation. The present results suggest that at group level, fronto-parietal coupling of the delta and alpha rhythms progressively
becomes abnormal though MCI and mild AD. Future longitudinal research should evaluate whether the present EEG approach is able to predict
the cognitive decline in individual MCI subjects.