2014) and other drowsiness (Allen et al., 2012). Finally, the intermittent occurrence of mass excursions is similar to other ex- perimental results that suggest that the emergence of critical dynamics, canoni- cal resting-state networks, and even BOLD activity is not a continuous process, but is driven by instantaneous events at the level of functional connections or in the activity profiles of brain regions, themselves (Tagliazucchi et al., 2012a; Liu and Duyn, 2013; Allan et al., 2015; Karahano˘ glu and Van De Ville, 2015). Presently, however, the precise neurobiological relevance of the high- versus low-modularity states remains unclear. An intriguing lead in this regard is the apparent importance of somatosensory and visual networks, which participate disproportionately often in excursions and are, hence, more temporally vari- able than expected. Interestingly, functional connections between these systems have also been reported as being highly variable across scan sessions (Laumann et al., 2015). Future work is needed to determine if mass excursions are driven by dynamic events involving these networks or another subset of connections. red It should be noted that modularity scores, Q , are in general, biased by a network’s total connection weight. The modularity function used here has a particular bias wherein networks with strong, positive connection weights will tend to have higher modularity scores. In this light, one might anticipate our observation that episodes of high modularity tend to coincide with periods when dynamic connections are unexpectedly strong. Nonetheless, having many positive connections does not, by itself, guarantee a large Q ; for that to occur, these positive connections also must be distributed in such a way that they cluster into communities. Our results are in line with earlier work by (Thompson and Fransson, 2015) and Zalesky and Breakspear (2015), indicating that a great deal of what we 24 Possible improvements