The threat of pain elicits a defensive parasympathetic response, characterised by heart rate deceleration, but also increased sympathetic arousal. Subjective appraisal and prediction of stimulus intensity is pivotal to the ability to enact adaptive behaviour and psychological response, usually mediated by changes in physiological arousal. It is of particular interest to understand how explicit pain cues influence arousal and subjective anxiety during the anticipation of pain. The objective of this study was to evaluate the influence of expectancies and stimulus intensity on self-reported and electrophysiological responses to repeated, painful thermal stimuli in humans. Thirty-two healthy individuals participated (50% female, aged 22 years, SD = 3.35). They were randomised to receive written instructions containing either a detailed (“Hint” group) or sparse (“No Hint” group) description of the relationship between the colour of a visual cue (pink, orange, purple, or aqua) and the intensity of the following thermal stimuli (32°C, 42°C, or 45°C). Cues were presented for 4s, followed by a 4s stimulus application on the lateral and medial cutaneous nerves of the dominant forearm using Medoc Pathway system (Ramat Yishay, Israel). Ratings of anticipatory anxiety, pain intensity and pain unpleasantness (0 to 10; least to most anxious, painful, unpleasant), cardiovascular reactivity (heart rate; beats per minute) and the galvanic skin response (GSR) were recorded during the cued anticipation period for one block of 24 stimuli. The effects of instruction group and cue on subjective anxiety and electrophysiological responses were assessed with separate repeated-measures ANOVAs. A significant interaction effect between the instruction group and visual cue was found for self-reported anxiety. The “Hint” group reported higher anxiety (High = 4.17±3.24, Low = 2.25±1.91, No = 0.93±1.24, Unknown = 3.02±2.55) compared to the “No Hint” group (High = 1.30±1.57, Low = 1.05±1.41, No = 1.41±1.81, Unknown = 1.42±2.06) (F(2.134,30) = 12.402, p < .001). On the contrary, there was a significant interaction between group and visual cue for average GSR recording, with the “No Hint” group displaying greater levels of physiological arousal than the “Hint” group; (F(2.136,30) = 3.271, p = .041). There were no significant differences or interactions between group and cue regarding cardiovascular reactivity, or pain intensity/unpleasantness ratings of the stimuli. We found that although explicitly anticipating painful events induced increased subjective anxiety, being unaware of the relationship between cues and stimulus intensity induced greater physiological arousal. These findings emphasise the role of cuing and anticipatory anxiety in preparation for a potentially painful stimulus, suggesting that anxiety in clinical settings may be lowered with reduced priming of the patient.
Tracy, L.M., Gibson, S.J., Georgiou-Karistianis, N., & Giummarra, M.J. (2015). Impact of explicit cuing on anxiety and arousal during the anticipation of thermal pain. Anaesthesia and Intensive Care. 43(3): 380-411.