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Browsing by Author "Thai, Michelle"

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    Interplay among Neural, Autonomic, and Neuroendocrine Systems in Rumination
    (2022-07) Thai, Michelle
    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.
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    Interplay Between Frontolimbic Resting State Connectivity And Hypothalamic-Pituitary-Adrenal Axis Functioning In Adolescents With And Without Depression
    (2019-03) Thai, Michelle
    Depression is associated with abnormalities in HPA-axis functioning and neural circuitry that underlie the stress response. Although positive associations have been found between cortisol levels and amygdala metabolism, activation, and volume, the associations between cortisol and resting state functional connectivity (RSFC) has not been examined. RSFC captures intrinsic connections between brain regions that may set the stage for the rallying of the HPA system. The association between frontolimbic RSFC in particular and HPA axis functioning is critical since stress system functioning involves activating to and recovering from threat, processes mediated by limbic and prefrontal activity respectively. The purpose of this study was to examine the association between cortisol and frontolimbic RSFC in healthy controls and adolescents with depression. Overall, healthy controls tended to show positive correlations between frontolimbic connectivity and cortisol levels in the context of the TSST whereas patients with depression showed an inverse relationship. Positive association between neural and HPA stress systems in healthy controls may suggest coordinated upregulation and downregulation of these two stress systems in response to stress. In contrast, in patients with depression, excessive recruitment of the mPFC by the amygdala may interfere with HPA system recruitment efficiency and successful rallying of HPA axis in response to social stress. These findings provide evidence that the intrinsic quality of this frontolimbic channel is related to HPA axis functioning, and patients with MDD show different patterns of associations compared to HC, which may interfere with adaptive stress functioning.