Brain networks are decoupled from external stimuli during internal cognition

Our cognition can be directed to external stimuli or to internal information. While there are many different forms of internal cognition (mind-wandering, recall, imagery etc.), their essential feature is independence from the immediate sensory input. This is thought to be reflected in the decoupling of brain networks from the external stimuli, but a quantitative investigation of this remains outstanding. Here we present a conceptual and analysis framework that links stimulus responses to connectivity between brain networks. This allows us to quantify the coupling of brain networks to the external stimuli. We tested this framework by presenting subjects with an audiovisual stimulus and instructing them to either attend to the stimulus (external task) or engage in mental imagery, recall or arithmetic (internal tasks) while measuring the evoked brain activity using functional MRI. We found that stimulus responses were generally attenuated for the internal tasks, though they increased in a subset of tasks and brain networks. However, using our new measure of coupling, we showed that brain networks became increasingly decoupled from the stimulus, even in the subset of tasks and brain networks in which stimulus responses increased. These results quantitatively demonstrate that during internal cognition brain networks are decoupled from external stimuli, opening the door for a fundamental and quantitative understanding of internal cognition.