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Lookup NU author(s): Dr Camillo Porcaro
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
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 PBRwas 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. (C) 2016 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license.
Author(s): Mayhew SD, Mullinger KJ, Ostwald D, Porcaro C, Bowtell R, Bagshaw AP, Francis ST
Publication type: Article
Publication status: Published
Print publication date: 01/06/2016
Online publication date: 05/03/2016
Acceptance date: 29/02/2016
Date deposited: 11/07/2016
ISSN (print): 1053-8119
ISSN (electronic): 1095-9572
Publisher: Academic Press
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