Oscillatory synchronization between different brain regions can be quantified with several procedures. Coherence, one of the most popular synchronization measures, describes the linear similarity between two EEG/MEG time-series at a given frequency.34 Examples of more advanced markers of functional coupling are the Synchronization Likelihood, which is sensitive to both linear and non-linear interdependencies between EEG/MEG signals, and the Phase Lag Index, which overcomes the problem of volume conduction, whereby neighboring electrodes detect common sources, spuriously increasing synchronization.13 Functional networks can be constructed by taking signals recorded at different regions as network nodes, and their mutual synchronization as connection strengths (Figure 3).13 Subsequently, these networks can be analyzed using graph theoretical algorithms, as outlined in the section 2.4.
