This has led some to suggest that regions involved in the default network are actually suppressed

by the active task. In other words, the appearance of increased activity in the passive task is really better conceived as a suppression of activity by the active task. In a thoughtful description of one such form of hypothesized suppression, Corbetta and colleagues14 proposed that “deactivation” of certain regions overlapping the default network may be party caused by high tonic activity associated with the locus coeruleus/noradrenergic system. The locus coeruleus is a small midbrain nucleus that modulates cortical Inhibitors,research,lifescience,medical and subcortical brain activity through diffuse excitatory monoaminergic (norepinephrine) projections. During task-focused Inhibitors,research,lifescience,medical states, a decrease in tonic activity of the locus coeruleus to moderate levels, combined with an increase in task-locked transient activity, may promote optimal engagement in the immediate task.15 During passive task states, the system is characterized by a high tonic baseline. Deactivation of certain regions within the default network may be linked to activity modulation of the locus coeruleus

as a mechanism of modulating the locus of attention. It has been difficult to rule out the possibility that certain networks are actively suppressed by focused, attentionally demanding tasks and XL184 supplier further that such suppression is the central Inhibitors,research,lifescience,medical cause of the observation of a “default network.” Adding a further complexity, studies of the monkey using intrinsic optical imaging of visual cortex suggest

that anticipatory arousal can modulate blood flow (the basis of positron emission tomography, [PET], and functional Inhibitors,research,lifescience,medical MRI [fMRI] measures) via neuronal mechanisms that are distinct from the transient activity modulations, which are the target of task-based neuroimaging studies.16 While it is unclear how such Inhibitors,research,lifescience,medical a physiological observation relates to the default network observed in the human imaging studies, the observation of a sustained anticipatory signal raises the possibility of a class of attentional effects that are insufficiently understood and that may be the source of the default network’s activity pattern during passive task states. Nonetheless, there is a favorably-alternative hypothesis that extends the ideas of Andreasen MTMR9 and colleagues.8 Internal mentation During passive moments, when demands to engage the external environment are relaxed, the mind wanders.17,18 Self-report data from neuroimaging tasks that activate the default network reveal that mind wandering and spontaneous thoughts occur frequently.8,19,20 When probed, the participants report that they are often thinking about future plans or about recent personal events. Rarely do they report attending to stimuli in the environment. Imagined events tend to be practical and free of fantasy-like qualities.