Dissertations, Theses, and Capstone Projects

Date of Degree

9-2017

Document Type

Dissertation

Degree Name

Ph.D.

Program

Psychology

Advisor

Elizabeth F. Chua

Committee Members

Hanah Chapman

Natalie Kacinik

Laura Rabin

Deborah Walder

Subject Categories

Biological Psychology | Cognitive Psychology

Keywords

VLPFC, Emotion, Memory, TMS, tDCS, Attention

Abstract

Emotional stimuli can have both beneficial and detrimental effects on memory, such that emotional stimuli can be distracting from current neutral working memory goals, while also leading to enhanced episodic memory for the distracting emotional stimuli. Recent evidence suggests that the ventrolateral prefrontal cortex (VLPFC) has multiple roles in the enhancing effects of emotion on memory through top-down/controlled processes, including 1) coping with negative distraction and 2) elaborative encoding of negative information. Additionally, previous research has alluded to hemispheric differences in the VLPFC (Chapter 1). However, previous research has been correlational, with no strong laterality tests of the VLPFC. Two experiments tested the roles of the left and right VLPFC in working memory and/or episodic memory tasks two using non-invasive brain stimulation techniques; transcranial direct current stimulation (tDCS) was used to increase cortical excitability of the VLFPC in Experiment 1 and transcranial magnetic stimulation (TMS) was used to inhibit the VLPFC in Experiment 2. Experiment 1 (Chapter 2) used tDCS to test whether the VLPFC is involved in working memory and episodic memory, and whether there are hemispheric differences. Results showed that the tDCS over left VLPFC led to improved working memory tasks with both neutral and negative distractors, and also indicated that there might be a greater demand on the VLPFC with negative distraction. The right VLPFC played a role in linking together working memory and episodic memory performance. Experiment 2 (Chapter 3) used TMS to test whether the involvement of the VLPFC in “emotional enhancement of episodic memory effect” was: 1) dependent on the available attentional resources, and 2) dependent on valence and/or arousal. Inhibiting the right VLPFC led to a reduced emotional enhancement of episodic memory effect for both “negative arousing” and “negative nonarousing” words. In contrast, inhibiting the left VLPFC under full attention reduced the emotional enhancement of episodic memory effect for “negative nonarousing” words only, suggesting that the role of the left VLPFC is dependent upon stimulus type and controlled processing. Together, these results point to a role for the VLPFC in: 1) working memory for both negative and neutral information, and 2) enhanced episodic memory for emotional stimuli, which is likely related its role in controlled processing. Additionally, our results show hemispheric differences, and suggest that the left VLPFC is important for controlled processing, whereas the right VLPFC is important for controlled and automatic processing.

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