Normalization of coherence

I wonder if the following procedure of normalization of coherence is acceptable.

  1. Get coherence for each ROI pair for each time window for each subject in Brainstorm.
  2. Get coherences among all Desikan-Killiany scouts for the entire epoch time window for each subject in Brainstorm. Compute mean and SD of these coherences.
  3. Normalize the ROI coherence (#1) with the mean and SD (#2) for each subject.

This is to minimize inter-subject variations, inspired by the paper by Nicolo 2015 Brain:
“Between-subject variation in synchronization magnitude can be due to variations in signal-to-noise ratios of the recordings. To avoid this potential confound in our analyses of the association between variations in [coherence] and clinical improvement, we normalized [coherence] map. This was achieved by subtracting, for each subject, the mean [coherence] across all voxels of the subject and by dividing by the standard deviation, hence yielding z-scores.”

I'm not sure you should compare (or average) coherence values between two different pairs or ROIs...

@Sylvain @pantazis: Can you please comment on that?