Abstract
The mechanisms causing cognitive problems in chronic pain patients are not well understood. We used the Stroop color word task (SCWT) to investigate distraction-induced analgesia, cognitive performance, and cerebral activation patterns in 29 fibromyalgia (FM) patients (mean age 49.8 years, range 25–64 years) and 31 healthy controls (HC) (mean age 46.3 years, range 20–63 years). In the first study, SCWT was used to investigate distraction-induced analgesia in FM patients. Two versions of the task were applied, one with only congruent color-word images and one with incongruent images. Pressure pain thresholds were assessed using a pressure algometer before, during, and following SCWT. In the second study, reaction times (RTs) were assessed and functional magnetic resonance imaging (fMRI) was used to investigate cerebral activation patterns in FM patients and HC during the SCWT. An event-related task mixing incongruent and congruent images was used. In study one, we found reduced pressure pain sensitivity during SCWT in both groups alike and no statistically significant differences were seen between the incongruent and congruent conditions. The study two revealed longer RTs during the incongruent compared to the congruent condition in both groups. FM patients had longer RTs than HC in both conditions. Furthermore, we found a significant interaction between group and congruency; that is, the group differences in RTs were more pronounced during the incongruent condition. This was reflected in a reduced activation of the caudate nucleus, lingual gyrus, temporal areas, and the hippocampus in FM patients compared to HC. In conclusion, we found normal pain inhibition during SWTC in FM patients. The cognitive difficulties seen in FM patients, reflected in longer RTs, were related to reduced activation of the caudate nucleus and hippocampus during incongruent SCWT, which most likely affected the mechanisms of cognitive learning in FM patients.
Highlights
Fibromyalgia (FM) is a chronic pain syndrome, many FM patients suffer from disturbed sleep, fatigue, mood disorders and cognitive impairment
Patients and 292 kPa in healthy controls (p,0.0001) at baseline and the absolute Pressure pain thresholds (PPTs) was lower in FM patients compared to controls at all times during incongruent as well as congruent Stroop Color Word Test (SCWT) (p,0.0001)
The normalized PPTs were higher at all times during incongruent SCWT compared to baseline in both groups (p,0.0001) and at 10 minutes following the SCWT in both groups (p = 0.001)
Summary
Fibromyalgia (FM) is a chronic pain syndrome, many FM patients suffer from disturbed sleep, fatigue, mood disorders and cognitive impairment. The poor performance of FM patients was not related to disturbances in mood or sleep [6,7,8], but has been reported to correlate with high pain intensity [6] and high pain sensitivity [8]. Pain intensity has been shown to influence cognitive task performance in chronic pain patients using a Stroop paradigm [9]. The authors hypothesized that overlapping networks are responsible for executive functioning tasks and pain processing, and that resources taken up by pain processing in FM patients would explain the inability to activate these networks during cognitive tasks [10]
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