Abstract Introduction Insomnia causes substantial health-care cost burden and is a risk factor for neurocognitive impairment. Increased DMN activity has been implicated in the hyperarousal theory of insomnia. In this pilot clinical trial, DMN was targeted via the left inferior parietal lobe using a brief 40 second cTBS Transcranial Magnetic Stimulation (rTMS). We hypothesized that neurocognitive improvements due to cTBS would be mediated by polysomnographic (PSG) parameters of slow wave sleep. Methods Twenty participants (12 female; age=26.9, SD=6.6 years) meeting criteria for insomnia completed a counterbalanced sham-controlled crossover design in which they served as their own controls on two separate nights of in-laboratory assessments. Sessions for both conditions included neurocognitive assessments at baseline, after stimulation (cTBS/sham) before bed, and the following morning. After stimulation, participants were allowed an 8-hour sleep opportunity from 2300 to 0700 monitored with PSG. The symbol coding and digit span subtests of the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) exam are the main assessments in the current investigation. Results Improvements in attention and processing speed were observed after a night of sleep following both active TMS (cTBS; B = 11.05, p < .001) and sham TMS conditions (B = 8.10, p = .002) the prior day. In the cTBS condition only, these improvements in attention were mediated by latency to slow wave sleep (N3), such that shorter latencies were related to greater improvements on a simple attention task (RBANS digit span; B = -0.75, p < .001). This effect of night to morning improvement in attention and processing speed was also found in the sham condition for the coding task (B = 60.81, p < .001), but not for digit span. No effects of slow wave sleep duration on RBANS coding or digit span were observed in either condition. Conclusion Improvements in simple attention performance in response to cTBS may be, in part, due to slow wave sleep parameters. Moreover, results suggest that simple attention may have been more sensitive to the effects of cTBS, whereas processing speed may have been a factor of lower slow wave sleep onset latency. Support (if any) DoD PRMRPD W81XWH2010173