Local build-up of sleep pressure could trigger mind wandering: Evidence from sleep, circadian and mind wandering research

Mind wandering (MW), or having thoughts unrelated to the task at hand, is a very pervasive phenomenon. Although research on MW has exponentially grown during the last decade and a half, the mechanisms behind this omnipresent phenomenon remain largely unknown. In this review, we will discuss some factors that have been shown to contribute to the occurrence of MW: the quality of sleep, the time of day when the task is performed, the chronotype of the individual and the duration of the task. The intriguing commonality between these specific factors is that they all suggest a relation between MW and sleep pressure. In line with recent work relating MW to local sleep-like activity, we here will argue that one of the mechanisms underlying the pervasiveness of MW might be the local build-up of homeostatic sleep pressure that inevitably occurs during task performance in the brain areas related to the task. Mind wandering could then occur not only to serve a biological purpose, e.g. brain protection, but also a functional one, e.g. off-line learning, that can be beneficial for behavioral performance.