1 2 Evidence for the Default Network ’ s Role in Spontaneous Cognition 3 4 5

35 36 A set of brain regions known as the default network increases its activity when 37 focus on the external world is relaxed. During such moments, participants change their 38 focus of external attention and engage in spontaneous cognitive processes including 39 remembering the past and imagining the future. However, the functional contributions of 40 the default network to shifts in external attention versus internal mentation have been 41 difficult to disentangle because the two processes are correlated under typical 42 circumstances. To address this issue, the present study manipulated factors that promote 43 spontaneous cognition separately from those that change the scope of external attention. 44 Results revealed that the default network increased its activity when spontaneous 45 cognition was maximized but not when participants increased their attention to 46 unpredictable foveal or peripheral stimuli. To examine the nature of participants’ 47 spontaneous thoughts, a second experiment used self-report questionnaires to quantify 48 spontaneous thoughts during extended fixation epochs. Thoughts about one’s personal 49 past and future comprised a major focus of spontaneous cognition with considerable 50 variability. Activity correlations between the medial temporal lobe and distributed 51 cortical regions within the default network predicted a small, but significant, portion of 52 the observed variability. Collectively, these results suggest that during passive states, 53 activity within the default network reflects spontaneous, internally-directed cognitive 54 processes. 55 56