Amplitude envelope correlation: methods

Hi, I have read about AEC methods from this paper:

  • They describe 2 methods bellow, I wonder which one is used in Brainstorm?
  • During AEC computation continuous data is divided into epochs, what is the default length of the epoch in Brainstorm?
  • In order to remove linear dependencies from the signal and control for source leakage, did you apply orthogonalization in Brainstorm?
  1. AEC: The timecourses of bandpass filtered electrical activity at the
    seed and test voxels were Hilbert transformed to obtain the
    analytic signal. The absolute value of the analytic signal was then
    determined in order to give the envelope of oscillatory power in
    the frequency band of interest. This we term the Hilbert envelope
    and this technique has been used extensively in previous MEG
    studies (for a mathematical description see Brookes et al., 2004).
    The Hilbert envelopes for the seed and test voxels were divided
    into n time segments of equal length Δ. The Pearson correlation
    coefficient between seed and test Hilbert envelopes was computed
    within each segment. This gave n correlation values, one for each
    time segment. These were then averaged across segments yielding
    a single average value which we term Averaged Envelope
    Correlation (AEC).

  2. CAE: The timecourses of electrical activity at both the seed and test
    voxels were Hilbert transformed and the Hilbert envelopes computed.
    The Hilbert envelopes were divided into n time segments of
    equal length Δ and the average value of the envelope computed
    within each time window. This resulted in two new temporally
    averaged Hilbert envelope timecourses, each comprising n points
    (we term these the ‘averaged envelopes’). The Pearson correlation
    between these averaged envelopeswas then computed as ameasure
    of FC which we term Correlation of Average Envelopes (CAE).

At the moment there are two implementations in Brainstorm:

@hossein27en Can you please clarify the differences between these functions, and how they match the cited reference?

Thanks, I used older one.

@niko808080 @Francois

Please read this post for a brief comparison between two Envelope Correlation functions.