The partial correlation is not a good method to control for specific connectivity rather than volume conduction. Covariance within a set of voxels, even after adjusting for correlations to other voxels (i.e., partial correlation) may still be volume conduction. The way to deal with volume conduction is with phase delays because phase delay = 0 for volume conduction. If phase is significantly greater than zero, then it is not volume conduction. Other methods to control for volume conduction are the Laplacian that looks at the local voltage gradient near each electrode rather than a global volume conduction condition. The Laplacian = 0 there are no local gradients. Also, lagged coherence is another method where phase difference = 0 is not computed.