Abstract
BackgroundThere is growing interest in the nature of slow variations of the blood oxygen level-dependent (BOLD) signal observed in functional MRI resting-state studies. In humans, these slow BOLD variations are thought to reflect an underlying or intrinsic form of brain functional connectivity in discrete neuroanatomical systems. While these ‘resting-state networks’ may be relatively enduring phenomena, other evidence suggest that dynamic changes in their functional connectivity may also emerge depending on the brain state of subjects during scanning.Methodology/Principal FindingsIn this study, we examined healthy subjects (n = 24) with a mood induction paradigm during two continuous fMRI recordings to assess the effects of a change in self-generated mood state (neutral to sad) on the functional connectivity of these resting-state networks (n = 24). Using independent component analysis, we identified five networks that were common to both experimental states, each showing dominant signal fluctuations in the very low frequency domain (∼0.04 Hz). Between the two states, we observed apparent increases and decreases in the overall functional connectivity of these networks. Primary findings included increased connectivity strength of a paralimbic network involving the dorsal anterior cingulate and anterior insula cortices with subjects' increasing sadness and decreased functional connectivity of the ‘default mode network’.Conclusions/SignificanceThese findings support recent studies that suggest the functional connectivity of certain resting-state networks may, in part, reflect a dynamic image of the current brain state. In our study, this was linked to changes in subjective mood.
Highlights
The success of functional magnetic resonance imaging as a non-invasive brain mapping technique has relied on its ability to detect local changes in evoked neural activity that are expressed indirectly in the blood oxygen level-dependent (BOLD) response [1]
This was first suggested in functional magnetic resonance imaging (fMRI) studies of primary sensory cortices, where it was shown that these regions could be distinguished on the basis of their spontaneously correlated activity patterns under resting-state conditions [8,9,10,11,12]. These findings have since been extended to other higher cortical systems comprising putative language, attention and memoryrelated regions [6,13,14,15,16,17] and have been recently identified in studies using independent component analysis (ICA); a data-driven technique that has shown value in isolating these networks from common artifacts in the fMRI time-series [18,19,20,21,22]. These findings indicate that many of the brain systems that are routinely implicated in task-related fMRI experiments can be defined on the basis of their ongoing spontaneous activities, or as distinct ‘resting-state networks’ (RSNs)
There is growing interest in spontaneous fluctuations of the fMRI-BOLD signal and its potential to encode an intrinsic form of brain functional connectivity in discrete brain systems
Summary
The success of functional magnetic resonance imaging (fMRI) as a non-invasive brain mapping technique has relied on its ability to detect local changes in evoked neural activity that are expressed indirectly in the blood oxygen level-dependent (BOLD) response [1]. A recent departure from this approach has been to examine the socalled ‘resting-state’ dimension of fMRI and the appearance of slow synchronous variations of the BOLD signal (,0.04 Hz) that occur prominently in the absence of external stimulation or tasks [3] Current interest in these slow fluctuations in fMRI studies centers on the belief that they may represent some underlying or intrinsic form of brain functional connectivity in discrete neuroanatomical systems [4,5,6,7]. While these ‘resting-state networks’ may be relatively enduring phenomena, other evidence suggest that dynamic changes in their functional connectivity may emerge depending on the brain state of subjects during scanning
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
