Abstract
A growing number of brain imaging studies show functional connectivity (FC) between regions during emotional and cognitive tasks in humans. However, emotions are accompanied by changes in physiological parameters such as heart rate and respiration. These changes may affect blood oxygen level-dependent signals, as well as connectivity between brain areas. This study aimed to clarify the effects of physiological noise on the connectivity between areas related to the default mode network using resting-state functional magnetic resonance imaging (rs-fMRI). Healthy adult volunteers (age range: 19–51 years, mean age: 26.9 ± 9.1 years, 8 males and 8 females) underwent rs-fMRI for 10 min using a clinical 3T scanner (MAGNETOM Trio A Tim System, Siemens) with simultaneously recorded respiration and cardiac output. Physiological noise signals were subsequently removed from the acquired fMRI data using the DRIFTER toolbox. Image processing and analysis of the FC between areas related to the default mode network were performed using DPARSF. Network-Based Statistic (NBS) analysis of the functional connectome of the DMN and DMN-related area was used to perform three groups of comparison: without physiological noise correction, with cardiac noise correction, and with cardiac and respiratory noise correction. NBS analysis identified 36 networks with significant differences in three conditions in FC matrices. Post hoc comparison showed no differences between the three conditions, indicating that all three had the same networks. Among the 36 networks, strength of FC of 8 networks was modified under physiological noise correction. Connectivity between left and right anterior medial frontal regions increased strength of connectivity. These areas are located on the medial cerebral hemisphere, close to the sagittal sinus and arteries in the cerebral hemispheres, suggesting that medial frontal areas may be sensitive to cardiac rhythm close to arteries. The other networks observed temporal regions and showed a decrease in their connectivity strength by removing physiological noise, indicating that physiological noise, especially respiration, may be sensitive to BOLD signal in the temporal regions during resting state. Temporal lobe was highly correlated with anxiety-related respiration changes (Masaoka and Homma, 2000), speech processing, and respiratory sensation. These factors may affect the rs-fMRI signaling sensitivity.
Highlights
Neuroimaging studies in humans have identified key areas for various emotions, as well as functional connectivity (FC) between brain regions (Maddock et al, 2003; Greicius et al, 2007; Zhi et al, 2018)
Prior to investigating the influence of pulse rate (PR) or respiratory rate (RR) on the eight FC, we evaluated the temporal changes in 600-s blood oxygen leveldependent (BOLD) signals from both sides of the superior medial frontal gyri, both sides of the anterior cingulate gyri, left median cingulate gyri, left inferior parietal gyrus, left supramarginal gyrus, right supramarginal gyrus, left angular, right precuneus, left middle temporal gyrus_temporal pole, left inferior temporal gyrus, and right inferior temporal gyrus that were nodes with significantly differences (Supplementary Figure S3)
This study aimed to clarify the effects of physiological noise on the default mode network (DMN) and DMN-related network, and the effect of physiological noise correction on the strength of their FC
Summary
Neuroimaging studies in humans have identified key areas for various emotions, as well as functional connectivity (FC) between brain regions (Maddock et al, 2003; Greicius et al, 2007; Zhi et al, 2018). Functional neuroimaging studies have focused on how negative emotions are inhibited, for example, when participants perform mindfulness tasks concentrating on breathing cycles (Tang et al, 2015). Strengthening of the FC between the DMN areas has been shown to improve mindfulness or/and selfcognitive skills (Brewer et al, 2011; Hasenkamp and Barsalou, 2012), and these effects might be associated with changes in the physiological state. These neuroimaging studies present evidence for the benefits of these tasks in our daily life, how these physiological changes affect blood oxygen leveldependent (BOLD) signals and brain region connectivity is unknown.
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