Reduced selective learning in patients with fibromyalgia vs healthy controls.

Impaired selective fear learning has been advanced as a core mechanism involved in excessive spreading of protective responses such as pain-related fear and avoidance leading to disability in chronic pain conditions. Using the litmus test for selective learning effects, the blocking procedure, we tested the hypothesis that patients with fibromyalgia (FM) show less selective threat learning than healthy controls (HCs). We introduce a novel selective learning task based around a clinical diary scenario. On a trial-by-trial basis, participants rated whether they expected certain situations (A, B, Z, and X) in the diary of a fictive FM patient would trigger pain in that patient. The procedure did not involve any experimental pain induction because the verbal outcomes "pain" or "no pain" were used. During the elemental acquisition phase, one situation was followed by "pain" (A+, eg, "Kim slept badly, and reports pain"), whereas another situation was followed by "no pain" (Z-, eg, "Kim was stressed, and reports no pain"). During the compound acquisition phase, another situation (X), referred to as the blocked stimulus, was presented in compound with a previously pain-eliciting situation and also paired with "pain" (AX+, eg, Kim slept badly" and "Kim has vacuumed," and reports pain). Simultaneously, a novel situation was introduced and also followed by "pain" (B+). Within-group comparisons showed blocking (ie, significant difference between B and X) in the HCs, but not in the patients with FM. This study is the first in directly assessing differences in selective learning between patients with FM and HCs using a blocking procedure.