Spontaneous default network activity reflects behavioral variability independent of mind-wandering

The brain's default mode network (DMN) is comprised of regions that are highly active during wakeful rest. In the past 15 y, the DMN has been a target of investigation in thousands of basic and clinical neuroscience studies, yet the fundamental role of this network remains debated and unknown. Some studies suggest that DMN activity increases with self-reported mind-wandering away from the present sensory environment, a state in which task performance tends to be highly unstable. However, we show that DMN activity increases with stable, rather than variable, behavior, independent from increases with mind-wandering. Our work urges reinterpretation of the significance of DMN activity fluctuations in daily life and DMN disruption in disease.