Browsing by Author "Powers, John Paul"
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Item Open Access Effects of repetitive transcranial magnetic stimulation on resting-state connectivity: A systematic review.(NeuroImage, 2020-05) Beynel, Lysianne; Powers, John Paul; Appelbaum, Lawrence GregoryThe brain is organized into networks that reorganize dynamically in response to cognitive demands and exogenous stimuli. In recent years, repetitive transcranial magnetic stimulation (rTMS) has gained increasing use as a noninvasive means to modulate cortical physiology, with effects both proximal to the stimulation site and in distal areas that are intrinsically connected to the proximal target. In light of these network-level neuromodulatory effects, there has been a rapid growth in studies attempting to leverage information about network connectivity to improve neuromodulatory control and intervention outcomes. However, the mechanisms-of-action of rTMS on network-level effects remain poorly understood and is based primarily on heuristics from proximal stimulation findings. To help bridge this gap, the current paper presents a systematic review of 33 rTMS studies with baseline and post-rTMS measures of fMRI resting-state functional connectivity (RSFC). Literature synthesis revealed variability across studies in stimulation parameters, studied populations, and connectivity analysis methodology. Despite this variability, it is observed that active rTMS induces significant changes on RSFC, but the prevalent low-frequency-inhibition/high-frequency-facilitation heuristic endorsed for proximal rTMS effects does not fully describe distal connectivity findings. This review also points towards other important considerations, including that the majority of rTMS-induced changes were found outside the stimulated functional network, suggesting that rTMS effects tend to spread across networks. Future studies may therefore wish to adopt conventions and systematic frameworks, such as the Yeo functional connectivity parcellation atlas adopted here, to better characterize network-level effect that contribute to the efficacy of these rapidly developing noninvasive interventions.Item Open Access Emotion Regulation Through Distancing: Developing a Novel Neurocognitive Model(2019) Powers, John PaulDistancing is a type of emotion regulation that involves simulating a new perspective to alter the psychological distance and emotional impact of a stimulus. The effectiveness and versatility of distancing make it a promising skill for clinical applications. However, the specific neurocognitive mechanisms of this emotion regulation tactic are poorly defined relative to the broader strategy of reappraisal. More focused investigation of these mechanisms would promote further understanding of the processes underlying distancing and potentially improve its applications. Therefore, I first synthesized literature on the component processes of distancing to propose a preliminary neurocognitive model. I tested the neural architecture of this model through a meta-analysis of fMRI literature, and then further validated and refined it by comparing three forms of distancing in an fMRI study. Finally, I investigated self-projection and its relation to the left temporoparietal junction using transcranial magnetic stimulation. The results of this work supported the neural architecture of the proposed model and suggested subtle differences in the recruitment of parietal regions across forms of distancing. No conclusions could be drawn regarding the specific functional contribution of the left temporoparietal junction, but I found that distancing performance was facilitated by repeated use, reinforcing the utility of this tactic for applied contexts. This model contributes new insights into the neurocognitive mechanisms of distancing, informs the optimal use of this tactic, and provides a framework for future research and interventions.