The Impact of the Threat Probability NPU Paradigm on Fear and Anxiety: a Startle, SCR and HR NPU study

Abstract

The defensive response system is a crucial part of mammalian physiology, responsible for recognizing, reacting, and coping with imminent or potential dangers. The defensive system is closely connected with many of our physiological systems, orchestrating a plethora of responses, but the key emotional responses to potential dangers are fear and anxiety. Numerous other studies have explored the defensive response system, leading to the rise of paradigms, like the no threat, predictable threat, unpredictable threat design. A study by Bradford et al., 2014 explored the manipulation of fear and anxiety defensive states through probability of threat, however, there were potential confounding variables. This study seeks to correct those confounds and validate the results of their study. 49 (2 excluded, n=47) participants between the ages of 18-35 were recruited. During the study, each participant’s startle and skin conductance responses, heart rate variability, and EEG measures were recorded to verify the physiological state elicited by the procedure. The 30-minute experiment exposed participants to trials of one out of three conditions. Startles and shocks were administered depending on the condition. Repeated measure ANOVAs were utilized to process the startle, skin conductance, and heart rate responses. The analyses found a significant increase in startle and skin conductance responses during predictable (certain) trials, and a significant decrease in heart rate during all conditions, specifically between the predictable and no-threat condition. Startle and heart rate results were contrary to the initial hypothesis, and skin conductance results supported the initial hypothesis. Factors like difference in the duration and level of threat most likely were the cause of these results. Our study demonstrates the importance of designing defensive response studies while accounting for difference in duration and level of threat and the benefits of collecting a variety of physiological responses to determine specific defensive states.