[FieldTrip] PAC analysis with ft_crossfrequencyanalysis

[Elisa Tatti]

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)?
  2.
  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.
  4.
  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').
  7.
  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



Elisa Tatti, Ph.D.

Post Doctoral Research Fellow

CUNY, School of Medicine

160 Convent ave

10031

New York City, NY



Tel. +1 3472043952


 pronouns: she/her/hers



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