The global signal in fMRI: Nuisance or Information?

The global signal is widely used as a regressor or normalization factor for removing the effects of global variations in the analysis of functional magnetic resonance imaging (fMRI) studies. However, there is considerable controversy over its use because of the potential bias that can be introduced...

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Bibliographic Details
Published in:NeuroImage (Orlando, Fla.) Fla.), 2017-04, Vol.150, p.213-229
Main Authors: Liu, Thomas T., Nalci, Alican, Falahpour, Maryam
Format: Article
Language:English
Subjects:
Brain Mapping - methods
Data processing
fMRI
Functional magnetic resonance imaging
General linear model
Global signal
Humans
Image Processing, Computer-Assisted - methods
Magnetic Resonance Imaging - methods
Motion
NMR
Noise
Nuclear magnetic resonance
Nuisance
Physiological noise
Physiology
Time series
Vigilance
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Summary:The global signal is widely used as a regressor or normalization factor for removing the effects of global variations in the analysis of functional magnetic resonance imaging (fMRI) studies. However, there is considerable controversy over its use because of the potential bias that can be introduced when it is applied to the analysis of both task-related and resting-state fMRI studies. In this paper we take a closer look at the global signal, examining in detail the various sources that can contribute to the signal. For the most part, the global signal has been treated as a nuisance term, but there is growing evidence that it may also contain valuable information. We also examine the various ways that the global signal has been used in the analysis of fMRI data, including global signal regression, global signal subtraction, and global signal normalization. Furthermore, we describe new ways for understanding the effects of global signal regression and its relation to the other approaches.
ISSN:1053-8119
1095-9572
DOI:10.1016/j.neuroimage.2017.02.036