The aim of this study was to characterize the dynamic
functional connectivity of resting-state electroencephalographic
(EEG) activity in Alzheimer’s disease (AD). The
magnitude squared coherence (MSCOH) of 50 patients
with dementia due to AD and 28 cognitively healthy
controls was computed. MSCOH was estimated in epochs
of 60 s subdivided in overlapping windows of different
lengths (1, 2, 3, 5 and 10 s; 50% overlap). The effect of
epoch length was tested on MSCOH and it was found that
MSCOH stabilized at a window length of 3 s. We tested
whether the MSCOH fluctuations observed reflected
actual changes in functional connectivity by means of
surrogate data testing, with the standard deviation of
MSCOH chosen as the test statistic. The results showed
that the variability of the measure could be due to
dynamic functional connectivity. Furthermore, a significant
reduction in the dynamic MSCOH connectivity of
AD patients compared to controls was found in the delta
(0–4 Hz) and beta-1 (13–30 Hz) bands. This indicated
that AD patients show lesser variation in neural connectivity
during resting state. Finally, a correlation between
relative power and standard deviation was found, suggesting
that an increase/peak in power spectrum could be
a pre-requisite for dynamic functional connectivity in a
specific frequency band.
