Ultimately, the crucial question is to what degree surface potentials or Laplacian estimates can represent genuine brain activity. Using EEGs recorded from a large sample (N = 130) during a visual half-field paradigm, we found that CSDs revealed by far a more accurate representation of hemifield-dependent asymmetries of the posterior contralateral N1, both in time and time-frequency domains, than their surface potentials counterparts, regardless of reference scheme (average, nose, linked mastoids, reference electrode standardization technique [REST]; Kayser and Tenke, 2015). In contrast, surface potentials also revealed significant hemifield-dependent asymmetries at more anterior locations, which were presumably caused by volume conduction. Likewise, using forward simulations of sine and cosine waveforms originating from subdural and deep local generators, signal fidelity in topography and phase of the measured amplitude spectra was superior for CSD compared to surface potentials, even for deep generators (Tenke and Kayser, 2015). Moreover, posterior alpha rhythms observed at rest, during task performance or as event-related desynchronizations were consistently and appropriately represented by CSD measures when systematically compared to surface potentials (Tenke and Kayser, 2015).
