Fear and pain: investigating the interaction between aversive states.

Pain and fear often co-occur and appear to interact, although the nature and direction of their relation is not clearly delineated. The present study investigates how exposure to the experience of one of these states subsequently affects responding to the other. Pressure stimulation and carbon dioxide-enriched air (CO2) were used to induce pain and fear, respectively, in 48 healthy individuals. The order in which the stimuli were introduced was manipulated, as was the CO2 level. Measures of overt behavior, physiological responding, and self-report were obtained; analyses of stimuli effects generally supported their ability to produce pain or fear. Results indicate that the stimulus rated as the most aversive, the higher level of CO2, led to the highest levels of distressed responding across dependent measures. This pattern was replicated for the stimuli found to be less aversive (i.e., pressure stimulation and low-level CO2, respectively). The authors conclude that fear and pain, in and of themselves, do not dictate the nature of their interaction; the most important factor is how aversive they are perceived to be in relation to one another.