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ALFF

RE: Adjusting the frequency band for ALFF in conn

Mar 7, 2017 07:03 AM
Alfonso Nieto-Castanon
McGovern Institute for Brain Research. MIT

RE: Adjusting the frequency band for ALFF in conn

Dear John,

Yes, exactly, the frequency of interest in ALFF and fALFF measures in CONN is typically defined just by the band-pass filter specified in the Denoising tab.

In addition, you can also use the frequency-decomposition framework in CONN if you wish for example to break down ALFF measures over a set of different frequencies of interest, and/or perform more complex frequency-specific analyses. For example, you could define two new conditions (e.g. "lowfreq" and "highfreq") in Setup.Conditions each covering two different segments of your frequency of interest (e.g. [.01 .05] and [.05 .10] respectively), and then simply select these two conditions when running the first-level ALFF analyses, and you will get two different ALFF measures for each subject covering the corresponding low/high frequencies. In this case (for conditions that have been defined using the 'frequency-decomposition' options in CONN) the effective frequency of interest of ALFF measures will be the intersection between each condition-specific frequency-window and the general frequency-window of interest specified in the Denoising step.

Hope this helps clarify
Alfonso

Originally posted by John Broulidakis:
Dear Alfonso and other conn toolbox experts,

Following the release of V17b I was delighted to see the addition of ALFF added to an already well stoked software package.

However, it is not clear to me from the release notes how you specify the frequency band of interest? Is this done simply by adjusting the frequency band of the bandpass filter?

Many thanks,

John

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