Date of Award

5-2025

Document Type

Thesis

Degree Name

Master of Arts (MA)

College/School

College of Humanities and Social Sciences

Department/Program

Psychology

Thesis Sponsor/Dissertation Chair/Project Chair

Alexandra M. Gaynor

Committee Member

Michael Bixter

Committee Member

Erica Nahin

Abstract

High-definition transcranial direct current stimulation (HD-tDCS) directly modulates brain activity, allowing the study of brain-behavior relationships in cognitive processes. However, cognitive effects of tDCS vary widely, partly due to individual differences in baseline brain activity. Estrogen levels, which fluctuate during the menstrual cycle, are known to affect cortical excitability and impact neural response to tDCS, but no research to date has examined the potential moderating role of endogenous estrogen in tDCS effects on cognition. In this study, N = 16 healthy female adults completed four sessions of a working memory (WM) task while receiving tDCS (two active sessions, two sham) over the left dorsolateral prefrontal cortex during high and low estrogen phases of their menstrual cycles. Since tDCS effects on cognition may vary due to endogenous estrogen levels, and high estrogen has been associated with higher cortical excitability, we hypothesized that tDCS effects on WM performance would be greater during high estrogen phases compared to low estrogen phases. Results showed that estrogen levels did interact with tDCS effects to influence WM performance; however, direction of effects were mixed and also varied by WM load. These results have important implications for the development of future tDCS interventions for female populations and suggest that females may benefit from having stimulation sessions aligned with specific menstrual cycle phases.

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