I have 96 channel EEG data.
When I compute channel-based magnitude-squared coherence between C3-C4, I get coherence values around 0.3.
When I compute source-based magnitude-squared coherence between precentral L and precentral R, I get coherence values around 0.04.
Why is the source-based coherence so much lower than channel-based? Is it because the source-based coherence is an average of coherence values between all individual vertices, as opposed to combined signals for channels?
When I compute source-based imaginary coherence between precentral L and precentral R, I get coherence values around 0.003.
Is imaginary coherence so much lower than magnitude-squared coherence, because it eliminates the effects of the volume conduction?