[FieldTrip] PAC analysis with ft_crossfrequencyanalysis

Elisa Tatti Elisatatti at msn.com
Thu Apr 7 15:59:08 CEST 2022

Dear Fieldtrip community,
I am writing because I am trying to compute for the first time the theta-beta phase-amplitude coupling using Fieldtrip.
After getting the Fourier spectrum with ft_freqanalysis, I computed the modulation index  (Tort et al., 2010) implemented in ft_crossfrequencyanalysis.

I still have a lot of doubts about this analysis and I really hope someone could be so kind to help me.
Here are some questions:

  1.   What is the minimum epoch length required to compute PAC (is 1s enough to compute the phase of 4 Hz)?
  3.  Is this computation suitable for tasks with a strong event-related synchronization? I read that ERPs should be subtracted from this analysis to avoid confounding effects but here I have reaching movements.
  5.  When computing PAC with Fieldtrip, I get the same value for the entire frequency band of the phase (i.e. same number from 4 to 8 Hz). This is despite the resulting MI matrix being N.channel*N.freqphase*N.freqAmplitude.
  6.  Since I would like to explore which theta frequency phase is mostly coupled with the higher frequency power, I would like to know why I get the same values and how to fix this as I could not find any configuration about averaging frequencies (e.g. cfg.averageoverfreq = 'yes'/'no').
  8.  If I manage to compute a meaningful MI, how do I statistically test whether it is significant?
  9.  Last but not least, is there a physiological or computational explanation for the impossibility of computing PAC on different electrodes?

Thank you very much for taking the time to read my questions. I really hope to get some answers from you.

Best wishes.


Elisa Tatti, Ph.D.

Post Doctoral Research Fellow

CUNY, School of Medicine

160 Convent ave


New York City, NY

Tel. +1 3472043952

 pronouns: she/her/hers

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