Influence of emotionally loaded visual and gustatory stimuli on pain perception.

Background/aims Previous studies have focused on the effect of negative emotions generated by music, pictures or odours on pain perception. This study tested whether emotionally loaded visual and gustatory stimuli could influence experimental tonic jaw muscle pain in healthy subjects. Methods 32 healthy subjects (16 men, 16 women; 18-39 years old) participated. In two sessions experimental jaw muscle pain was evoked by injection of 0.2 ml hypertonic saline into the masseter muscle. In the first session with each injection an emotion (positive, negative or neutral) was generated by visual stimuli (pictures taken from International Affective Picture System). In the second session, emotions were generated by gustatory stimuli (75% sucrose = sweet, 0.1% quinine = bitter, or tasteless gelatine). The participants continuously rated pain intensity (electronic visual analogue scale - VAS) as well as mood and unpleasantness/pleasantness of the conditioning stimuli (visual/ gustatory). Results and conclusion Hypertonic saline evoked moderate levels of pain in all subjects (mean peak VAS = 5.2 ± 2.4). During conditioning with negatively loaded pictures VAS pain scores were increased (19.3%) compared with neutral (p = 0.03) and positive emotions (p = 0.001). There was a linear relation between negative emotions and VAS pain scores (r = 0.40, p = 0.02). Although there was a tendency, no significant effect was observed during positive pictures in comparison with neutrals (p = 0.1). Surprisingly no effect on VAS pain scores was observed during neither negative (p = 0.1) nor positive (p = 0.2) gustatory stimuli. This may be due to failure of the gustatory stimuli to generate a change in emotions. These results suggest that not all conditioning stimuli are potent modifiers of emotions, which seem to be a prerequisite for effects on pain perception.