Investigating Heterogeneous Associations in Fear Responses Among PTSD Patients Using Quantile Regression Restricted; Files Only

Mar, Hanna (2017)

Permanent URL: https://etd.library.emory.edu/concern/etds/rx913q57p?locale=en
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Abstract

Post traumatic stress disorder (PTSD) is a heterogeneous disorder with characteristics

including a heightened fear response or a reduced ability to inhibit fear in safe

situations. The mechanisms that lead to this response are not fully understood. Fear

Potentiated Startle (FPS) is a tool often used to study fear response by exposing patients

to visual cues that are associated with safety and danger, and measuring their

startle responses (Jovanovic et al., 2005). This thesis will use quantile regression to

conduct a secondary analysis of fear responses to better understand the heterogeneous

associations between potential covariates and heightened startle response. Study participants

were recruited at a large hospital in Atlanta, GA, and were predominately

from a low-income, urban area. Participants were asked to complete questionnaires to

assess past trauma and current PTSD symptoms before undergoing fear potentiated

startle experiments. Startle response measurements were recorded in response to the

safety and danger cues during fear acquisition, and for early, mid, and late fear extinction.

Gender and reexperiencing symptoms were found to influence the distribution of startle

response to the safety cue at higher quantiles, but not at the lower or middle quantiles.

At the 75th quantile females experienced a 27.31 (p = 0.004) point increase in startle

response compared to males, and a one point increase in reexperiencing symptoms

was associated with a 2.39 (p = 0.049) point increase in startle response to the safety

cue. The effect of childhood trauma on the 75th quantile of the safety cue was also

signicant (p = 0.036). No covariates were found to be signicantly different from

zero at lower or middle quantiles of the startle response to the danger cue. At the

75th quantile, gender was associated with a 30.53 (p = 0.003) point increase in startle

response to the danger cue. A one point increase in reexperiencing symptom severity

was associated with a 4.27 (p = 0.003) point increase in startle response to the danger

cue, while a one point increase in hyperarousal symptom severity was associated

with and 3.03 (p = 0.028) point decrease in startle response to the danger cue. These

results demonstrate that gender and reexperiencing symptoms play an important role

in influencing the startle response to the safety and danger cues for patients with high

startle responses. Subjects with high startle responses to the danger cue may also be

differentiated by hyperarousal symptom severity. Future studies on subjects who have

high startle responses may help to further understand the heterogeneity of PTSD.

Table of Contents

1 Introduction 1

2 Methods 3 2.1 Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 Clinical Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2.1 Traumatic Events Inventory (TEI) . . . . . . . . . . . . . . . . 4 2.2.2 PTSD Symptom Scale (PSS) . . . . . . . . . . . . . . . . . . . . 4 2.3 Fear Potentiated Startle . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.4 Quantile Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.5 Statistical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.5.1 Univariate Quantile Regression . . . . . . . . . . . . . . . . . . 9 2.5.2 Multivariate Quantile Regression . . . . . . . . . . . . . . . . . 9 2.5.3 Model Fitting and Variable Selection Process . . . . . . . . . . 9 3 Results 10 3.1 Univariate Quantile Regression . . . . . . . . . . . . . . . . . . . . . . . 11 3.2 Multivariate Quantile Regression . . . . . . . . . . . . . . . . . . . . . . 12 3.2.1 Safety Cue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2.2 Danger Cue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4 Discussion 14 5 Conclusion 17 References 18 Tables 22 Figures 30 Appendix 37

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