Pain catastrophizing is associated with dental pain in a stressful context

Abstract

Pain is associated with anxiety in a dental setting. It has remained unclear how cognitive-affective factors modulate pain and anxiety in a stressful context, such as receiving dental procedures. We hypothesized that both the situational factor (unpredictability about painful stimuli) and the trait factor (pain catastrophizing, i.e., the tendency to interpret pain in negative orientation) account for dental pain. Fifteen healthy participants were recruited to perform an associative learning task. They were asked to learn the pairing between visual cues and the intensity of incoming painful stimuli delivered at the right upper central incisor. Brain activation associated with pain was recorded by functional magnetic resonance imaging (fMRI). The participants reported increased anxiety and pain in the stressful context, where stimuli intensity was not predicted by the preceding cue. The score of the Pain Catastrophizing Scale was positively correlated with the increased pain modulated by unpredictability. Brain activation at the right posterior hippocampus, a region critically related to associative learning of aversive stimuli and context, was correlated with the individual catastrophizing level. Our findings suggest that both the situational factor (unpredictability) and the trait factor (catastrophizing) influence dental pain, highlighting the role of cognitive-affective factors in pain control of dental patients.

Figure 1.

Experimental design and scanning protocol. (A) Experimental design. Each trial consisted of an anticipatory phase followed by a pain phase and ended with a rest phase. The anticipatory phase was initiated by 1 of 2 types of visual cues, which differed in predictability of the pain intensity of the impending stimulus and thus induced different levels of anticipatory anxiety. The high-predictability cue (P) was always followed by a single low-intensity painful stimulus (LI). The low-predictability cue (UnP) was followed by either a low-intensity (as above) or high-intensity (HI) painful stimulus. Overall, each of the cue-intensity events (LI-P, LI-UnP, and HI-UnP) was presented in equal numbers (20 trials) throughout the experiment. Participants were instructed that 2 types of cues would be displayed during functional scanning, and that attention should be paid to the cue-intensity association. Two sessions were performed, with 30 event-cycles per session and a five-minute rest between 2 sessions. Two fixed sequences were generated in which stimuli were randomly presented. The order of sequences with respect to sessions was counterbalanced across participants. (B) Scanning protocol. The visual cue was displayed throughout the anticipatory phase (mean duration = 8 sec) and pain phase (mean duration = 10.5 sec), with a 10-msec electrical pulpal stimulus. After the stimulus was delivered, the visual cue was replaced by a visual-analog scale (VAS) for the following rest phase (mean duration = 12 sec). In this phase, participants were required to rate the pain intensity of the stimulus just received via an online response box. The discrete 11-point pain intensity scale with verbal anchors used for psychophysical calibration and stimulus evaluation during functional scanning ranged from 0 (no pain) to 10 (intolerable pain). After scanning, participants rated pain-related anxiety based on a 0- to 5-point scale, in which ‘0’ represented ‘no anxiety about the impending pain’ and ‘5’ represented ‘extreme anxiety about the impending pain’.

Figure 2.

Summary of main results. (A) Behavioral results. The score of the Pain Catastrophizing Scale predicted the exacerbated pain modulated by increased unpredictability) (left panel) but not that modulated by increased nociceptive intensity (right panel). (B) ROI analysis. The posterior (red) and anterior (green) hippocampus each occupied 1/3 of the hippocampus ROI (see Appendix for ROI definition), and ROI analysis was performed for the anterior and posterior hippocampus (left panel). The PCS score was positively correlated with brain activation in the contrast image in the posterior hippocampus (framed with a red border), but not the anterior hippocampus (N.S.), of the right hemisphere (right panel). (C) Whole-brain analysis. Brain regions with activation positively correlated with PCS were found at the right hippocampus in the contrast (LI-UnP > LI-P), consistent with the finding from the above ROI analysis. The color bar indicates the Z score from a voxel-wise comparison of brain activation between the 2 conditions.

Figure 3.

A proposed cognitive-affective model regarding exacerbated pain in a stressful context. Increased unpredictability, a situational factor, evokes both heightened pain-related anxiety (A) and increased pain (B), resulting in a stressful context (shaded by gray). The individual variation in the degree of magnified pain is predicted by the trait factor, pain catastrophizing (C). Note that the change of anxiety per se does not predict the change of pain. Participants with higher pain catastrophizing showed increased hippocampal activation, which is associated with memory and learning of aversive stimuli (D). The current model highlights that both the stressful context (modulated by unpredictability) and the catastrophizing trait are critical to pain experience in a stressful dental setting.