  We studied the interactions between different temporal scales of diffusion
processes on complex networks and found them to be stronger in scale-free (SF)
than in Erdos-Renyi (ER) networks, especially for the case of phase-amplitude
coupling (PAC)-the phenomenon where the phase of an oscillatory mode modulates
the amplitude of another oscillation. We found that SF networks facilitate PAC
between slow and fast frequency components of the diffusion process, whereas ER
networks enable PAC between slow-frequency components. Nodes contributing the
most to the generation of PAC in SF networks were non-hubs that connected with
high probability to hubs. Additionally, brain networks from healthy controls
(HC) and Alzheimer's disease (AD) patients presented a weaker PAC between slow
and fast frequencies than SF, but higher than ER. We found that PAC decreased
in AD compared to HC and was more strongly correlated to the scores of two
different cognitive tests than what the strength of functional connectivity
was, suggesting a link between cognitive impairment and multi-scale information
flow in the brain.
