The default mode network is most commonly shown to be active when a person is not focused on the outside world and the brain is at wakeful rest, such as during daydreaming and mind-wandering. But it is also active when the individual is thinking about others, thinking about themselves, remembering the past, and planning for the future. wikipedia 
See Brain Networks
Some have argued the brain areas in the default mode network only show up together because of the vascular coupling of large arteries and veins in the brain near these areas, not because these areas are actually functionally connected to each other.
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A newly published study gives some insight into what may be happening inside young children's brains in each of those situations. And, says lead author Dr. John Hutton, there is an apparent Goldilocks effect where some kinds of storytelling may be "too cold" for children, while others are "too hot." And, of course, some are "just right" to engage the default mode network. npr aaas