Does Pain Necessarily Have an Affective Component? Negative Evidence from Blink Reflex Experiments

Abstract

The experience of pain can be described using two dimensions – sensory and affective-motivational – of which the affective-motivational component is strongly modulated by context and the cognitive appraisal of pain. In pain research, the sensory component is commonly represented by ratings of pain intensity, while the affective component is represented by ratings of pain unpleasantness. However, there is evidence to suggest that test subjects tend to judge pain intensity different from unpleasantness whenever separate scales for both dimensions are presented concurrently. This study used a startle reflex as an objective measure of affective response to stimuli of varying intensities to determine whether the affective component can be abolished when predictable stimulation paradigms are applied.BACKGROUND: Experimental pain research has shown that the affective component of pain is influenced strongly by situational characteristics; affective pain processing appears to be particularly pronounced in situations that provoke a feeling of uncertainty and uncontrollability.OBJECTIVES: To determine whether the affective component of pain can be completely abolished if a ‘safe’, particularly predictable stimulation paradigm is applied.METHOD: Forty healthy volunteers recruited at the University of Bamberg (Bamberg, Germany) were assessed in two experiments. Tonic contact heat stimuli staged in three intensities (warmth, heat and pain) relative to the individual pain threshold was applied; these were predictable with regard to intensity and course, and the subjects had easy access to control. The startle reflex was assessed as an objective measure of affective response. In addition, the subjects provided unpleasantness ratings. To compare these results to a gold standard for affective response, affective pictures taken from the International Affective Picture System were presented during temperature stimulation in the second experiment.RESULTS: Both experiments showed no potentiation of the startle reflex under painful heat stimulation compared with the two nonpainful stimulus intensities (heat and warmth), although the painful stimulation was clearly rated as more unpleasant.CONCLUSIONS: Results suggest that it is possible to develop a ‘safe’ noxious stimulus, which is rated as clearly unpleasant, but lacks physiological indication of negative affect. This divergence might be explained by subjective ratings being influenced by the instructions. The possibility of reducing the pain affect by suggesting ‘safety’ may be of therapeutic interest.