Abstract
The default mode network (DMN) refers to regional brain activity that is greater during rest periods than during attention-demanding tasks; many studies have reported DMN alterations in patient populations. It has also been shown that the DMN is suppressed by scanner background noise (SBN), which is the noise produced by functional magnetic resonance imaging (fMRI). However, it is unclear whether different approaches to “rest” in the noisy MR environment can alter the DMN and constitute a confound in studies investigating the DMN in particular patient populations (e.g., individuals with schizophrenia, Alzheimer's disease). We examined 27 healthy adult volunteers who completed an fMRI experiment with three different instructions for rest: (1) relax and be still, (2) attend to SBN, or (3) ignore SBN. Region of interest analyses were performed to determine the influence of rest period instructions on core regions of the DMN and DMN regions previously reported to be altered in patients with or at risk for Alzheimer's disease or schizophrenia. The dorsal medial prefrontal cortex (dmPFC) exhibited greater activity when specific resting instructions were given (i.e., attend to or ignore SBN) compared to when non-specific resting instructions were given. Condition-related differences in connectivity were also observed between regions of the dmPFC and inferior parietal/posterior superior temporal cortex. We conclude that rest period instructions and SBN levels should be carefully considered for fMRI studies on the DMN, especially studies on clinical populations and groups that may have different approaches to rest, such as first-time research participants and children.
Highlights
Functional neuroimaging studies have identified a network of brain regions associated with the absence of a specific task or action that supports ongoing, internal modes of cognition (Raichle and Snyder, 2007; Buckner et al, 2008)
Typical default mode network (DMN) regions of interest (ROI) analyses determined that activation only in dorsal medial prefrontal cortex (dmPFC) was influenced by instructions regarding scanner background noise (SBN) during rest periods (Figure 3)
Weighted parameter estimates were significantly greater in dmPFC when participants were instructed to attend to SBN compared to the baseline phase ([attend > baseline], t(16) = 4.19, p < 0.001)
Summary
Functional neuroimaging studies have identified a network of brain regions associated with the absence of a specific task or action that supports ongoing, internal modes of cognition (Raichle and Snyder, 2007; Buckner et al, 2008). Studies using positron emission tomography (PET; Shulman et al, 1997; Raichle et al, 2001) and functional magnetic resonance imaging (fMRI; Binder et al, 1999; Greicius et al, 2003) have found greater activity in the DMN during rest conditions as compared to active task conditions. These findings do not depend on a particular cognitive task; the DMN has been found to deactivate during visual tasks (e.g., Shulman et al, 1997; Mazoyer et al, 2001), auditory tasks (e.g., Mazoyer et al, 2001), language tasks (e.g., Mazoyer et al, 2001), and working memory tasks (e.g., Fransson, 2006)
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