Resting state of human brain measured by fMRI experiment is governed more dominantly by essential mode as a global signal rather than default mode network

• Resting-state fMRI BOLD signal of the human brain is a superposition of EM and DM. • EM (essential mode) is asymmetric and the most dominant mode for individuals. • DM (DMN-like mode) is the second dominant mode that holds the default mode network. • Both EM and DM are activated with low-frequency oscillations in the below 0.2 Hz. • The changes in active regions of the brain during motor-task are reflected in EM. Resting-state of the human brain has been described by a combination of various basis modes including the default mode network (DMN) identified by fMRI BOLD signals in human brains. Whether DMN is the most dominant representation of the resting-state has been under question. Here, we investigated the unexplored yet fundamental nature of the resting-state. In the absence of global signal regression for the analysis of brain-wide spatial activity pattern, the fMRI BOLD spatiotemporal signals during the rest were completely decomposed into time-invariant spatial-expression basis modes (SEBMs) and their time-evolution basis modes (TEBMs). Contrary to our conventional concept above, similarity clustering analysis of the SEBMs from 166 human brains revealed that the most dominant SEBM cluster is an asymmetric mode where the distribution of the sign of the components is skewed in one direction, for which we call essential mode (EM), whereas the second dominant SEBM cluster resembles the spatial pattern of DMN. Having removed the strong 1/f noise in the power spectrum of TEBMs, the genuine oscillatory behavior embedded in TEBMs of EM and DMN-like mode was uncovered around the low-frequency range below 0.2 Hz.