Date of Award
2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Psychology
First Advisor
Travis Todd
Abstract
During traumatic experiences, stimuli in the environment can become associated with the aversive event. Later, these stimuli can be used to retrieve the memories. Although forming fear memories is adaptive, in some cases retrieval of fear can be maladaptive, such as in fear-related disorders. Unwanted responses to memory retrieval cues can be reduced via extinction or counterconditioning. In extinction, the cue associated with the fearful memory is presented several times in the absence of the aversive outcome, resulting in a decrease of responding to the cue over time. This is the mechanism behind exposure therapy in humans. In counterconditioning, the cue is presented without the fearful outcome and is instead paired with the presentation of a positively valanced event, such as relaxation for humans. Although extinction and counterconditioning reduce responding, this reduction is not permanent. Indeed, responding is apt to return outside the context where extinction / counterconditioning occurred. This return of responding, known as “renewal”, is often considered a barrier to otherwise effective treatment (i.e., therapy) in humans. Many aspects of the renewal effect are still unknown. The experiments in the following dissertation aim to investigate multiple variables thought to impact renewal of conditioned fear responding including 1) sex and cycling ovarian hormones, 2) method of response reduction prior to renewal, and 3) role of the ventral hippocampus in renewal following counterconditioning. Experiments 1a and 1b aimed to test the impact of sex and cycling ovarian hormones on the renewal of conditioned fear following extinction. We report no statistical difference in ability to renew or magnitude of renewal effect in males, intact females, and ovariectomized females. Experiments 2a and 2b expanded this conclusion by repeating the experiments with counterconditioning and again found no difference in renewal effect between males, intact females, and ovariectomized females. These results are discussed with respect to the role of cycling ovarian hormones in renewal and the influence of context on behavior during either extinction or counterconditioning. Experiment 3 examined potential differences in extinction and counterconditioning as methods of response reduction and the subsequent renewal effect. Interest in using counterconditioning as a more effective form of response reduction has grown, though results are varied. A direct comparison of fear renewal following extinction and aversive-to-appetitive counterconditioning revealed that while counterconditioning reduced fear at a faster rate than extinction, the renewal effect was not statistically different. The results of this experiment suggest no difference in the efficacy of counterconditioning and extinction in preventing the renewal effect. Results are discussed in relation to conflicting literature and explores methodological differences that may contribute to different renewal outcomes based on method of response reduction. Experiment 4 examined VH involvement in fear renewal following counterconditioning and in contextual fear expression. Inhibitory DREADDs were used to reversibly inactivate the VH at renewal test following counterconditioning. The VH was also inactivated prior to a test session of contextual fear retrieval. Results showed no impact of VH inactivation on fear renewal but impaired expression of contextual fear. The results are discussed with respect to the VH in contextual information processing, including a discussion of conflicting findings in the literature.
Language
en
Number of Pages
148 p.
Recommended Citation
Moriarty, Samantha Kelly, "Renewal of fear in a third context: Impact of sex, response reduction method, and the ventral hippocampus" (2025). Graduate College Dissertations and Theses. 2111.
https://scholarworks.uvm.edu/graddis/2111