Functional connectivity in the resting brain: A network analysis of the default mode hypothesis
PET and fMRI studies have suggested that the resting brain has a default mode of internal (possibly conceptual) processing. The neural network underlying such a default mode has not been definitively demonstrated in the resting brain.
We analyzed the resting connectivity patterns of two nodes commonly implicated in this hypothetical network: the ventral anterior cingulate cortex (vACC) and the posterior cingulate cortex (PCC).
Fourteen adults (7 F/7 M, 18-25 years) were scanned on a 3T MRI scanner at rest and during a spatial 2-back working memory task (WM) and a checkerboard paradigm (passive viewing of a still versus flashing checkerboard).
vACC (blue arrow) showed significant resting state connectivity with: PCC, medial prefrontal cortex, orbitofrontal cortex, nucleus accumbens, and midbrain/hypothalamus.
PCC (red arrow) showed significant resting state connectivity with: vACC, inferior parietal cortex (bilaterally), medial prefrontal cortex, left dorsolateral prefrontal cortex, medial orbitofrontal cortex, left parahippocampal gyrus, and left inferolateral temporal cortex.
When the analyses were performed on the checkerboard data, the connectivity patterns for both vACC and PCC were nearly identical to those detected at rest.
The resting connectivity patterns for the vACC and the PCC link showed a number of commonly deactivated regions in a cohesive network. Replication of the connectivity patterns during a checkerboard paradigm confirmed that the network is not disrupted by low-level processing tasks. This network appeared to be tonically active during rest. These data provide the most direct evidence to date for a default mode neural network in the resting brain.
Greicius MD, Krasnow B, Reiss AL, Menon V. (2003). "Functional connectivity in the resting brain: A network analysis of the default mode hypothesis." Proc Natl Acad Sci U S A. Jan 7;100(1):253-8. Abstract - PDF