Neuroimaging techniques have demonstrated over the years their ability to
characterize the brain abnormalities associated with different neurodegenerative diseases.
Among all these techniques, magnetoencephalography (MEG) stands out by its high temporal
resolution and noninvasiveness. The aim of the present study is to explore the coupling
patterns of resting-state MEG activity in subjects with mild cognitive impairment (MCI). To
achieve this goal, five minutes of spontaneous MEG activity were acquired with a 148-
channel whole-head magnetometer from 18 MCI patients and 26 healthy controls. Interchannel
relationships were investigated by means of two complementary coupling measures:
coherence and Granger causality. Coherence is a classical method of functional connectivity,
while Granger causality quantifies effective (or causal) connectivity. Both measures were
calculated in the five conventional frequency bands: delta (d, 1-4 Hz), theta (q, 4-8 Hz), alpha
(a, 8-13 Hz), beta (b, 13-30 Hz), and gamma (g, 30-45Hz). Our results showed that
connectivity values were lower for MCI patients than for controls in all frequency bands.
However, only Granger causality revealed statistically significant differences between groups
(p-values < 0.05, FDR corrected Mann-Whitney U-test), mainly in the beta band. Our results
support the role of MCI as a disconnection syndrome, which elicits early alterations in
effective connectivity patterns. These findings can be helpful to identify the neural substrates
involved in prodromal stages of dementia.
