Perhaps the most influential issue with regard to recording is the choice of reference electrode (mastoids, earlobe, nose, average reference, local derivations, dura imaging), affecting how each signal represents shallower and deeper sources. For oscillation power, the effects may be not as crucial, however, for connectivity measures like coherence, substantial effects are expected (Peterson et al., 2019). Figure 2 shows how a change in reference from average to mastoid affects oscillation power and coherence in the alpha band. This required us to make explicit choices in the reference setup to harmonize the results across cohorts for studying the genetics of functional brain connectivity.
