Investigating Heterogeneous Associations in Fear Responses Among PTSD Patients Using Quantile Regression Público
Mar, Hanna (2017)
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 37About this Master's Thesis
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