Hope you are fine under this long-lasting pandemic.
I encountered some problems about phase-based connectivity, specifically dWPLI. Although I have gone through related teachings in your ANTS book and videos on Udemy, I still could not confirm some points when back to my data. Here are problems:
(1) How to understand negative values of dWPLI? Before baseline correction, I found that raw dWPLI values calculated from my data involved negative values. Because I focus on prestimulus session, I am not going to conduct baseline correction. Then are there any meanings for those negative values? How to deal with them?
(2) If I analyzed dWPLI, do I need to consider the confound of volume conduction? In my data, I found that in the subject level, when the dWPLI was low, the power in that time-frequency window was also low. It seemed to have a positive correlation. According to descriptions in Chapter 25.10 in ANTS book, that positive correlation may imply volume conduction. However, according to what you said in the 171st video on Udemy, phase lag index has no confounder of volume conduction. Back to my case, I first filtered data using surface Laplacian and then used insensitive measure, i.e. dWPLI. So even though there were positive correlations between dWPLI and power, I suppose it very probably reflected the true connectivity. Am I correct?
(3) How to interpret the results of phase-based connectivity? There were many reviews or studies related to it now. As a beginner, I still could not grasp the “boundary” of its interpretation. In other words, how to avoid over-interpretation or what is the safe area in which phase-based connectivity could be interpreted?
Looking forward to your reply.