Sustained attention that is effortful during challenging cognitive tasks has been associated with robust activity in brain areas involved with cognitive control, collectively referred to as the dorsal attention network (DAN). In contrast, the periods of optimal sustained attention have been associated with relatively less DAN activity than periods of struggle. Optimal sustained attention may be less dependent on DAN function and more dependent on brain networks related to task automation such as the default mode network (DMN). Alternatively, optimal sustained attention may be recruiting DAN function efficiently, thus resulting in less overall activity. These two hypotheses were examined by temporarily disrupting DAN activity by applying repetitive transcranial magnetic stimulation (rTMS) to the frontal eye fields (FEF) in the DAN and then measuring sustained attention to a cognitive task. Subjects randomly received real or sham rTMS to the left or right FEF and then performed a modified go/no-go sustained attention task referred to as the gradCPT. For subjects receiving real rTMS to the right FEF, response accuracy decreased and reaction time variability increased on the gradCPT during periods of optimal sustained attention. The findings suggest that optimal sustained attention to cognitive tasks is supported by the refined, economical recruitment of right hemisphere DAN function
