Default(y) Mode Network: Important regions of DMN do not survive alterations in flip angles

Abstract

AbstractThe default mode network (DMN) is thought to capture intrinsic activity of the brain and has been instrumental in understanding the dynamics of the brain. However, the DMN has not been without critics; both conceptual and empirical. The empirical criticisms caution against physiological noise as a source for the reported connectivity in the DMN. Smaller flip angles (FAs) have been modelled and shown to reduce physiological noise in BOLD signal recordings. A previous functional MRI (fMRI) study with flickering checkerboard stimuli, manipulated FAs to show that activity in the posterior-cingulate cortex (PCC) and precuneus is prone to physiological noise. This raises questions about studies that show activations in these areas (PCC and precuneus) with a fixed FA and the role of these areas in brain networks like DMN. Given the prominent role of PCC and precuneus in DMN, we studied the effect of FAs on the resting-state functional connectivity involving these areas in DMN. We used four FAs and recorded resting-state activity in a 3-T scanner. The results show PCC and precuneus BOLD functional connectivity is inconsistent. We lend support to previous empirical criticisms of DMN, linking its activity to physiological noise. Our results add to concerns about PCC and precuneus related BOLD activity and their putative role in DMN. Alongside previous studies we advocate using smaller flip angles as an empirical tool to investigate physiological noise in fMRI studies.