Task-related BOLD responses and resting-state functional connectivity during physiological clamping of end-tidal CO₂

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• 作者：C. Madjar^a ; ^{cecile.madjar@gmail.com} ; C.J. Gauthier^a ; ^b ; P. Bellec^a ; R.M. Birn^c ; J.C.W. Brooks^d ; R.D. Hoge^a ; ^b
• 关键词：End-tidal CO2 fluctuations ; Physiological noise ; Resting-state functional connectivity ; Task-related response ; Default-mode-network ; BOLD fMRI
• 刊名：NeuroImage
• 出版年：2012
• 期刊代码：83_10538119
• 类别：neu
• 出版时间：15 May, 2012
• 卷：61
• 期：1
• 页码：41-49
• 文件大小：1459 K

摘要

Carbon dioxide (CO₂), a potent vasodilator, is known to have a significant impact on the blood-oxygen level dependent (BOLD) signal. With the growing interest in studying synchronized BOLD fluctuations during the resting state, the extent to which the apparent synchrony is due to variations in the end-tidal pressure of CO₂ (PETCO₂) is an important consideration. CO₂-related fluctuations in BOLD signal may also represent a potential confound when studying task-related responses, especially if breathing depth and rate are affected by the task. While previous studies of the above issues have explored retrospective correction of BOLD fluctuations related to arterial PCO₂, here we demonstrate an alternative approach based on physiological clamping of the arterial CO₂ level to a near-constant value. We present data comparing resting-state functional connectivity within the default-mode-network (DMN), as well as task-related BOLD responses, acquired in two conditions in each subject: 1) while subject's PETCO₂ was allowed to vary spontaneously; and 2) while controlling subject's PETCO₂ within a narrow range. Strong task-related responses and areas of maximal signal correlation in the DMN were not significantly altered by suppressing fluctuations in PETCO₂. Controlling PETCO₂ did, however, improve the performance of retrospective physiological noise correction techniques, allowing detection of additional regions of task-related response and resting-state connectivity in highly vascularized regions such as occipital cortex. While these results serve to further rule out systemic physiological fluctuations as a significant source of apparent resting-state network connectivity, they also demonstrate that fluctuations in arterial CO₂ are one of the factors limiting sensitivity in task-based and resting-state fMRI, particularly in regions of high vascular density. This must be considered when comparing subject groups who might exhibit differences in respiratory physiology or breathing patterns.