help
help > RE: Correction for global signal
Aug 28, 2015 07:08 PM | Alfonso Nieto-Castanon - Boston University
RE: Correction for global signal
Hi Jeff,
That is a very interesting question. As far as I know (but I am not an expert on this topic so please take the following comments with a grain of salt) cerebral perfusion effects on the BOLD signal are, to a first-order approximation, modeled as additive (changes in the BOLD signal baseline) and/or multiplicative (changes in the BOLD signal scale or sensitivity to vascular and physiological sources) effects. For neither of these effects you would expect to need any additional correction in functional connectivity analyses, since: a) global additive differences between sessions in the BOLD signal are controlled by session-specific regressors and high-pass filtering steps -which remove the mean BOLD signal separately for each session- and by the mean-invariance property of the correlation measures -which also disregards mean BOLD signal levels-; and b) scaling/multiplicative differences between sessions in the BOLD signal are controlled by global signal scaling and the scaling-invariance property of the correlation measures -which disregard the actual scale/units of the BOLD signal- combined with the linear nature of all of the denoising steps -re-scaling the entire BOLD signal results in simply a re-scaled version of the denoised BOLD signal-. Of course other, more complex, effects may be at play beyond global BOLD signal baseline/scaling differences between the sessions, but I would behard-pressed to imagine an scenario where global signal regression would do a better job at correcting for these effects than aCompCor (but please let me know your thoughts or any additional details about possible perfusion-related differences that you may expect and I will be happy to comment specifically on how to best correct for those effects)
Best
Alfonso
Originally posted by Jeff Browndyke:
That is a very interesting question. As far as I know (but I am not an expert on this topic so please take the following comments with a grain of salt) cerebral perfusion effects on the BOLD signal are, to a first-order approximation, modeled as additive (changes in the BOLD signal baseline) and/or multiplicative (changes in the BOLD signal scale or sensitivity to vascular and physiological sources) effects. For neither of these effects you would expect to need any additional correction in functional connectivity analyses, since: a) global additive differences between sessions in the BOLD signal are controlled by session-specific regressors and high-pass filtering steps -which remove the mean BOLD signal separately for each session- and by the mean-invariance property of the correlation measures -which also disregards mean BOLD signal levels-; and b) scaling/multiplicative differences between sessions in the BOLD signal are controlled by global signal scaling and the scaling-invariance property of the correlation measures -which disregard the actual scale/units of the BOLD signal- combined with the linear nature of all of the denoising steps -re-scaling the entire BOLD signal results in simply a re-scaled version of the denoised BOLD signal-. Of course other, more complex, effects may be at play beyond global BOLD signal baseline/scaling differences between the sessions, but I would behard-pressed to imagine an scenario where global signal regression would do a better job at correcting for these effects than aCompCor (but please let me know your thoughts or any additional details about possible perfusion-related differences that you may expect and I will be happy to comment specifically on how to best correct for those effects)
Best
Alfonso
Originally posted by Jeff Browndyke:
Alfonso,
What if one were conducting a pre-/post- experiment in which global cerebral perfusion may be reasonably assumed to increase between baseline and follow-up? Would aCompCor still correct for this sort of global increase in components feeding the BOLD response?
Thanks,
Jeff
What if one were conducting a pre-/post- experiment in which global cerebral perfusion may be reasonably assumed to increase between baseline and follow-up? Would aCompCor still correct for this sort of global increase in components feeding the BOLD response?
Thanks,
Jeff
Threaded View
| Title | Author | Date |
|---|---|---|
| Natalia Yakunina | Jul 15, 2013 | |
| Alfonso Nieto-Castanon | Jul 18, 2013 | |
| Sascha Froelich | Sep 9, 2016 | |
| Nobody | Nov 20, 2020 | |
| Alfonso Nieto-Castanon | Sep 9, 2016 | |
| Ben R | Apr 8, 2020 | |
| Scott Burwell | Sep 9, 2016 | |
| Natalia Yakunina | Jul 23, 2013 | |
| Jeff Browndyke | Aug 29, 2015 | |
| Alfonso Nieto-Castanon | Aug 31, 2015 | |
| Jeff Browndyke | Aug 31, 2015 | |
| Jeff Browndyke | Aug 28, 2015 | |
| Alfonso Nieto-Castanon | Aug 28, 2015 | |
| Jeff Browndyke | Aug 29, 2015 | |