Psychology ETDs

Publication Date

Summer 8-1-2023


Those over the age of 65 occupy a growing proportion of the population. With this growth, cognitive issues that accompany aging are increasingly coming to the forefront, yet despite this focus, ways to ameliorate cognitive issues in older adults are lacking. Transcranial direct current stimulation (tDCS) offers one possibility for improving cognitive function in older adults, but tDCS application is hindered by individual factors that manifest as heterogeneity in outcomes across the literature. This is especially the case in older adults, where changes in anatomy and functionality provide a potential complication for tDCS application. Presented here are three studies seeking to explicate some of that heterogeneity. In Study 1, the behavioral effects of tDCS in older adults are delineated, specifically whether those with and without Mild Cognitive Impairment experience different effects. In healthy older adults, there was a main effect of active tDCS on task performance where accuracy was increased across all blocks. In those with MCI, an interaction between active tDCS and task block was observed, such that improvement in the task did not occur until after 20 minutes. In Study 2, finite element modeling of tDCS current flow was performed in order to understand how changes in white matter, grey matter, and cerebrospinal fluid impact the current introduced by tDCS. Among those who received active tDCS, significant relationships existed between white matter and cerebrospinal fluid ratios and task performance, with higher white matter and lower cerebrospinal fluid ratios predicting better performance in the active tDCS group. Lastly, higher electric field magnitude underneath the electrode was predictive of better task performance in the active stimulation group. In Study 3, differences in resting state functional connectivity at baseline were used to predict benefit following active tDCS. Consistent with findings of dedifferentiation in older adults, where functional connectivity patterns in older adults are less segregated than those in younger adults, stronger intraconnectivity in the front-parietal control network was predictive of better task performance in those who received active tDCS. Together, these results highlight how brain differences in older adults can affect tDCS application, and how understanding these differences can ensure that the potential benefits of tDCS in older adults are maximized.

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First Committee Member (Chair)

Dr. Vincent Clark

Second Committee Member

Dr. Jeremy Hogeveen

Third Committee Member

Dr. Davin Quinn

Fourth Committee Member

Dr. Sephira Ryman

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