The study investigates the neural mechanisms underlying mind-wandering, a ubiquitous phenomenon where the mind drifts from external tasks to internal thoughts. Using thought sampling and brain imaging, the researchers found that mind-wandering is associated with activity in a default network of cortical regions that are active during rest. Individuals' reports of mind-wandering were correlated with activity in this network. The default network, which remains active during passive sensory processing and attenuates during tasks with high central executive demand, was identified as a key region involved in mind-wandering. The study also showed that individuals who report frequent mind-wandering exhibit greater recruitment of the default network during tasks associated with high incidence of stimulus-independent thought (SIT). Additionally, the magnitude of BOLD signal increases in these regions during mind-wandering was positively correlated with individuals' self-reported daydreaming propensities. These findings suggest that the default network plays a crucial role in generating SIT and that mind-wandering may serve various cognitive functions, such as maintaining optimal arousal or facilitating mental time travel.The study investigates the neural mechanisms underlying mind-wandering, a ubiquitous phenomenon where the mind drifts from external tasks to internal thoughts. Using thought sampling and brain imaging, the researchers found that mind-wandering is associated with activity in a default network of cortical regions that are active during rest. Individuals' reports of mind-wandering were correlated with activity in this network. The default network, which remains active during passive sensory processing and attenuates during tasks with high central executive demand, was identified as a key region involved in mind-wandering. The study also showed that individuals who report frequent mind-wandering exhibit greater recruitment of the default network during tasks associated with high incidence of stimulus-independent thought (SIT). Additionally, the magnitude of BOLD signal increases in these regions during mind-wandering was positively correlated with individuals' self-reported daydreaming propensities. These findings suggest that the default network plays a crucial role in generating SIT and that mind-wandering may serve various cognitive functions, such as maintaining optimal arousal or facilitating mental time travel.