Abstract
FMRI BOLD responses to changes in neural activity are influenced by the reactivity of the vasculature. By complementing a task-related BOLD acquisition with a vascular reactivity measure obtained through breath-holding or hypercapnia, this unwanted variance can be statistically reduced in the BOLD responses of interest. Recently, it has been suggested that vascular reactivity can also be estimated using a resting state scan.This study aimed to compare three breath-hold based analysis approaches (block design, sine–cosine regressor and CO2 regressor) and a resting state approach (CO2 regressor) to measure vascular reactivity. We tested BOLD variance explained by the model and repeatability of the measures. Fifteen healthy participants underwent a breath-hold task and a resting state scan with end-tidal CO2 being recorded during both. Vascular reactivity was defined as CO2-related BOLD percent signal change/mmHg change in CO2.Maps and regional vascular reactivity estimates showed high repeatability when the breath-hold task was used. Repeatability and variance explained by the CO2 trace regressor were lower for the resting state data based approach, which resulted in highly variable measures of vascular reactivity.We conclude that breath-hold based vascular reactivity estimations are more repeatable than resting-based estimates, and that there are limitations with replacing breath-hold scans by resting state scans for vascular reactivity assessment.
Highlights
The blood-oxygenation-level-dependent (BOLD) signal that is acquired during functional magnetic resonance imaging is commonly used as a measure of neural activity in the brain
Pairwise comparisons revealed that the BHBlock design explained the BOLD time course significantly worse than the to differ between regions, the median model fit was extracted on a regional basis as well
We compared vascular reactivity maps obtained during the breath-hold scan to the maps obtained during the resting scan to see whether resting state scans could be potential replacements for breath-holds when it comes to estimating vascular reactivity
Summary
The blood-oxygenation-level-dependent (BOLD) signal that is acquired during functional magnetic resonance imaging (fMRI) is commonly used as a measure of neural activity in the brain. The nature of the BOLD signal makes it susceptible to changes in neural activity and depends in part on the reactivity of the cerebro-vascular system (for a review see Logothetis and Wandell, 2004). The BOLD signal following an increase in CO2 in a region can explain up to 50% of variance between participants in task-related BOLD responses in that region (Kannurpatti et al, 2012; Liu et al, 2013) This confound can cause problems for studies investigating task-dependent BOLD signals, in particular if group differences in vascular reactivity exist, for example, in the case when comparing older and younger participants (Handwerker et al, 2007; Riecker et al, 2003; Thomason et al, 2005)
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