Fear-learning deficits in subjects with fibromyalgia syndrome?

Abstract

Background: Fibromyalgia syndrome (FMS) is frequently associated with psychiatric conditions, particularly anxiety. Deficits in contingency learning during fear conditioning have been hypothesized to increase anxiety and, consequently, pain sensation in susceptible individuals. The goal of this study was to examine the relationship between contingency learning and pain experience in subjects with FMS and rheumatoid arthritis (RA).

Methods: Fourteen female FMS subjects, 14 age-matched female RA subjects and 14 age-matched female healthy controls (HCs) were included in a fear-conditioning experiment. The conditioned stimulus (CS) consisted of visual signs, the unconditioned stimulus (US) of thermal stimuli. CS- predicted low-temperature exposure (US), while CS+ was followed by low or high temperature.

Results: In the FMS group, only 50% of the subjects were aware of the US-CS contingency, whereas 86% of the RA subjects and all of the HCs were aware of the contingency. CS+ induced more anxiety than CS- in RA subjects and HCs. As expected, low-temperature exposure was experienced as less painful after CS- than after CS+ in these subjects. FMS subjects did not show such adaptive conditioning. The effects of the type of CS on heart rate changes were significant in the HCs and the aware FMS subjects, but not in the unaware FMS subjects.

Conclusions: Contingency learning deficits represent a potentially promising and specific, but largely unstudied, psychopathological factor in FMS. Deficits in contingency learning may increase anxiety and, consequently, pain sensation. These findings have the potential to contribute to the development of novel therapeutic approaches for FMS.

Figure 1

Experimental paradigm and time course of the conditioning experiment. Experimental paradigm (top): Visual cues predicted exposure to painful heat stimulation. Painful stimulation was delivered at a low temperature (LT) or at a higher, more painful temperature (HT). One visual cue (here: triangle) was consistently followed by a LT. Another cue (here: square) was followed by LT or HT. LF: low fear/ pain signal (CS−); HF: high fear/pain signal (CS+ _low or CS+ _high). The conditioned stimuli were presented during a variable amount of time (8 to 15 s) in order to increase the unpredictability of the unconditioned stimuli. The duration of the exposure to heat stimulation was 6 s. Self-reported fear and pain ratings were assessed in the intertrial intervals of 30 s. CS, conditioned stimulus; US, unconditioned stimulus.

Figure 2

Learning curves. Self-reported fear ratings after each trial classified by diagnostic group and kind of CS stimulus. The panels illustrate adaptive differential conditioning by higher fear responses to CS+ than to CS− in healthy controls and rheumatoid arthritis subjects, but not in fibromyalgia subjects. Error bars indicate standard errors of means (SEM).

Figure 3

Behavioural results. The means of the self-reported fear and pain ratings after CS− /low-temperature stimulation, CS+ /low-temperature stimulation and CS+ /high-temperature stimulation classified by diagnostic group (14 fibromyalgia subjects, 14 healthy controls, 14 rheumatoid arthritis subjects). Error bars indicate standard errors of means (SEM).

Figure 4

Heart rate results. Heart rate changes during the conditioned stimuli CS+ and CS−. The panels illustrate the heart rate change waveforms for the CS+ and CS− trials. Because the present study used a range of CS–US intervals (8–15 s), only the initial 8 s were used to estimate heart rate responses to the CS. The time point 0 s represents the s before CS onset. Heart rate responses of aware (7) and unaware (7) FMS subjects were analysed separately.