Thai, Michelle2022-09-262022-09-262022-07https://hdl.handle.net/11299/241704University of Minnesota Ph.D. dissertation. 2022. Major: Psychology. Advisor: Shmuel Lissek. 1 computer file (PDF); 174 pages.Rumination is a type of perseverative negative cognition that is associated with greater risk for depression and a worse prognosis. Current treatments for depression do not always adequately address symptoms of rumination. Novel, biologically-based treatments need to be developed. To develop such treatments, a thorough understanding of the mechanisms underlying rumination using multilevel approaches is necessary since processes like rumination implicate different neural and physiological systems which may constrain one another or have additive effects. This study took a multiple units of analysis approach to examine 1) neural connectivity and activation in the frontolimbic circuit and Default Mode Network (DMN), 2) heart rate variability (HRV), and 3) basal cortisol levels in the context of awakening in the context of a novel treatment for rumination incorporating mindful breathing training (MBT) and transcranial direct current stimulation (tDCS). This study explored 1) how rumination is related to these three systems and 2) how improvement in rumination relates to changes in these three systems. Overall, we find evidence that mindful breathing and tDCS can reduce rumination and depression as well as change these neurophysiological systems. Although these findings were not always clearly related to improvement in clinical symptoms, we find some evidence that tDCS and mindful breathing can increase HRV, decrease DMN and frontolimbic activation during a rumination induction task, increase frontolimbic RSFC, and increase positive mind wandering, which was generally associated with clinical improvement, generally more so or the tDCS group relative to sham. These results provide preliminary evidence that web-based mindfulness practices may have potential in reducing rumination and changing relevant neurophysiological systems.enBrain StimulationDepressionMindful BreathingMindfulnesstDCSTranscranial Direct Current StimulationThesis or Dissertation