Counterirritation by pain inhibits the responsiveness to aversive loud tones: the role of state anxiety and state fear triggered in the NPU paradigm.

Aim of the study: The application of a noxious stimulus reduces the perception and responsiveness to other pain stimuli. This inhibition can be experimentally assessed with a method called 'counterirritation'. The question arises if counterirritation acts also on the perception and responsiveness to aversive but non-nociceptive stimuli (e.g., loud tones). Since aversive stimulation is often associated with state anxiety or state fear, we investigated in addition the modulatory effects of these emotions on counterirritation.

Material and methods: 51 subjects participated in our study. We presented tones with aversive loudness (105 dB), first alone then during counterirritation (immersion of the hand in a hot water bath of 46 °C) to assess inhibition of loudness perception and responsiveness. Influences of state anxiety and state fear on counterirritation were investigated by using the Neutral-Predictable(fear)- Unpredictable(anxiety) Paradigm (NPU), which is based on classical conditioning. Loudness ratings (perception of the aversive tones) and startle reflex (defensive reaction to aversive tones) were assessed.

Results: Counterirritation reduced startle reflex amplitudes, but not the loudness ratings. Although state anxiety and state fear were successfully induced, counterirritation remained unaffected.

Conclusions: Our study showed that pain inhibits the responsiveness to aversive stimuli (loud tones). Thus, the postulate that 'pain inhibits pain' might be better changed to 'pain inhibits aversiveness'. Consequently, our findings may also question the assumption of a clear pain specificity in inhibitory action as assumed by theoretical approaches like 'conditioned pain modulation' (CPM). Furthermore, counterirritation appeared one more time resistant to the influence of negative emotions.