Question about inter-regional tPAC

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#1

Hello!

I am analysing EEG data looking for theta-gamma tPAC. I already got my results for standard tPAC (coupling of phase and amplitude within the same electrode) and now I want to broad my project by looking for inter-regional tPAC. However, I got no results when using the same parameters I used for the initial tPAC analysis.

These are the parameters:

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This is what I got for standard tPAC with those parameters for one single trial:

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And this is what I am getting for inter-regional tPAC with those exact parameters from the screenshot: (black for every electrode, even for the electrode I am using as a seed for fp (FT7), where I already know from the previous screenshot that there's some coupling between phase of FT7 and amplitude of FT7)

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However, if I increase the lenght of the sliding time window to 0.7s or if I change the theta frequency range from 3-6 to 3-8, I got results. These are by applying both changes simultaneously:

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Given that I have different results for the coupling between phase and amplitude in one particular electrode by using the two methods, I wonder whether they're calculating tPAC differently or if there's another reason why this is happening. Because I am broadening my initial analysis I'd like to maintain the same parameters so I don't know if I can obtain some results by maintaining them.

Thank you so much in advance!

#2

Hi,

Sadly, the IR tPAC code was released a bit hastily at the time (a few years back) and indeed the code is different than the other tPAC functions. Also, fixes related to filtering that were very recently made in tPAC were not applied to IR tPAC. Given our limited resources and our view that IR PAC is not a technique with well demonstrated results, we were actually planning on removing this from Brainstorm shortly. This would happen at the same time we fix other issues related to averaging in tPAC.

You're welcome to advocate for keeping this functionality, e.g. by sharing publications that demonstrate its usefulness. This is a bit outside my expertise, but I'd be happy to discuss it again with the group.

Cheers,
Marc

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#3

In addition to Marc's note, I can also mention that the discrepancies you are reporting between the tPAC and irPAC outcomes are certainly due to recent fixes we have brought up to tPAC, which essentially consisted in updating the filter parameters used in the process. Please see this thread.
As Marc mentioned, we have not elected to update irPAC accordingly and are considering retiring the process from the Brainstorm toolkit.

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