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Global signal modulation of single-trial fMRI response variability: effect on positive vs negative BOLD response relationship

Mayhew, Stephen D.; Mullinger, Karen J.; Ostwald, D.; Porcaro, C.; Bowtell, Richard W.; Bagshaw, Andrew P.; Francis, Susan T.

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Authors

Stephen D. Mayhew

Karen J. Mullinger

D. Ostwald

C. Porcaro

Richard W. Bowtell

Andrew P. Bagshaw

Susan T. Francis



Abstract

In functional magnetic resonance imaging (fMRI), the relationship between positive BOLD responses (PBRs) and negative BOLD responses (NBRs) to stimulation is potentially informative about the balance of excitatory and inhibitory brain responses in sensory cortex. In this study, we performed three separate experiments delivering visual, motor or somatosensory stimulation unilaterally, to one side of the sensory field, to induce PBR and NBR in opposite brain hemispheres. We then assessed the relationship between the evoked amplitudes of contralateral PBR and ipsilateral NBR at the level of both single-trial and average responses. We measure single-trial PBR and NBR peak amplitudes from individual time-courses, and show that they were positively correlated in all experiments. In contrast, in the average response across trials the absolute magnitudes of both PBR and NBR increased with increasing stimulus intensity, resulting in a negative correlation between mean response amplitudes. Subsequent analysis showed that the amplitude of single-trial PBR was positively correlated with the BOLD response across all grey-matter voxels and was not specifically related to the ipsilateral sensory cortical response. We demonstrate that the global component of this single-trial response modulation could be fully explained by voxel-wise vascular reactivity, the BOLD signal standard deviation measured in a separate resting-state scan (resting state fluctuation amplitude, RSFA). However, bilateral positive correlation between PBR and NBR regions remained. We further report that modulations in the global brain fMRI signal cannot fully account for this positive PBR-NBR coupling and conclude that the local sensory network response reflects a combination of superimposed vascular and neuronal signals. More detailed quantification of physiological and noise contributions to the BOLD signal is required to fully understand the trial-by-trial PBR and NBR relationship compared with that of average responses.

Journal Article Type Article
Acceptance Date Feb 29, 2016
Online Publication Date Mar 5, 2016
Publication Date Jun 1, 2016
Deposit Date Jun 23, 2016
Publicly Available Date Jun 23, 2016
Journal NeuroImage
Print ISSN 1053-8119
Electronic ISSN 1095-9572
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 133
DOI https://doi.org/10.1016/j.neuroimage.2016.02.077
Keywords Negative BOLD Response, Deactivation, Global Signal, RSFA
Public URL https://nottingham-repository.worktribe.com/output/787238
Publisher URL http://www.sciencedirect.com/science/article/pii/S1053811916001956

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