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Keywords:

  • behavioural approach system activity;
  • fibromyalgia;
  • personality;
  • somatic symptoms

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Author Contributions
  8. References

The first objective was to investigate the behavioural activity in the systems of Gray's theory; these are the Behavioural Inhibition System (BIS) and Behavioural Approach System (BAS), in fibromyalgia (FM) patients. The second aim was to assess in FM patients whether there is an association between BIS or BAS with self-reported somatic symptoms. Twenty FM patients and 20 healthy controls completed questionnaire measures of BIS and BAS activity (Sensitivity to Punishment and Sensitivity to Reward Questionnaire), self-reported somatic symptoms (Somatic Symptoms Scale Revised), positive and negative affect (Positive and Negative Affect Schedule) and health status (EuroQoL Visual Analogue Scale). The results showed that FM patients had lower Sensitivity to Reward (SR) scores than controls. The SR score correlated with different somatic symptoms groups. The partial correlation (controlling for other variables measured) showed that the SR score correlated specifically with musculoskeletal symptoms. Furthermore, in regression analysis, SR score significantly predicted musculoskeletal symptoms, after controlling for other variables measured in this study. Our findings suggest that FM patients show BAS hypoactivity. This BAS activity in FM is similar to patients with depression, where a lower BAS functioning has also been found. The BAS activity predicts the musculoskeletal self-reported symptoms in FM better than other measures included in this study. Although this is a preliminary study, it suggests the importance of BAS activity in FM.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Author Contributions
  8. References

Fibromyalgia (FM) is a chronic, debilitating and psychophysiologic disorder that afflicts predominantly middle-aged women, and etiology of which remains unknown. The American College of Rheumatology (ACR) criteria define fibromyalgia as a chronic disorder characterized by the presence of widespread pain accompanied by tenderness upon palpation at a minimum of 11 of 18 predefined tender points throughout the musculoskeletal system.[1] Recent studies suggest the importance of personality factors in FM. Some studies found characteristic traits in FM. Zautra et al.[2] found lower levels of extroversion and positive affect in FM patients. Glazer et al.[3] found a level of high harm avoidance traits in FM. Patients with FM in general have a sociotropic personality style similar to patients with major depressive disorder.[4] Others indicate an association between personality traits and cognitive performance of FM patients.[5] In addition, it appears that there are personality traits, such as harm avoidance, that are hereditary and that may contribute to the development of FM.[3]

The biological personality theory of Gray posits two main brain systems that regulate behavior in response to environmental stimuli.[6] The Behavioural Inhibition System (BIS) serves to alert the person to the possibility of danger or punishment, thereby enhancing avoidance behavior, whereas the Behavioural Approach System (BAS) is sensitive to signals of reward and is involved in approach behaviour. This personality theory appears to be associated with pain and somatic symptoms in the general population.[6] In the study conducted by Muris et al.[7] BIS and BAS activity were significantly related with the level of pain catastrophizing (the tendency to focus on pain and negatively evaluate one's ability to deal with pain) in adolescents. We have found differential associations between BIS, BAS and different self-reported somatic symptoms in university students.[8]

Although in FM the pain and somatic symptoms appear related to psychological states,[9] and recent studies suggest that one of the possible lines of research in FM should focus on the interrelationships between somatic symptoms and personality,[10] this possible relationship has not received much empirical attention. Specifically, the activity of BIS and BAS and its relationship with somatic symptoms has not been studied in FM. The first aim of the present study was to investigate the activity in the systems of Gray's model (BIS and BAS) in FM patients. The second aim was to assess whether there is an association between BIS or BAS with self-reported somatic symptoms in FM patients.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Author Contributions
  8. References

Participants

Forty women participated in the study. Twenty were patients with FM according to the ACR criteria,[1] aged between 44 and 61 years. In this group 17.6% were literate, 64.7% had primary education and 17.6% had secondary education. These participants were recruited from the Fibromyalgia Associations of Southern Spain. The control group was comprised of 20 healthy females, aged between 47 and 65 years; 20% of this group was literate and 80% had primary education. The participants of both groups did not suffer from other severe somatic or psychiatric diseases (such as cancer, psychotic disorders, etc.). All participants gave their informed consent for their participation (according to the Declaration of Helsinki).

Measures

To pursue the proposed objectives (and to control for the other relevant measures) the following tests were used:

The Sensitivity to Punishment and Sensitivity to Reward Questionnaire (SPSRQ)[11] comprised 48 yes/no items, divided in two scales. The Sensitivity to Punishment scale (SP) evaluates individual differences in BIS functioning, and the Sensitivity to Reward scale (SR) evaluates individual differences in BAS functioning.

The Somatic Symptoms Scale Revised (SSS-R)[12] comprises 90 items related to incidences in the last year of certain categories of somatic self-reported symptoms. It is divided into different subscales of symptoms (immunological symptoms, coronary symptoms, respiratory symptoms, stomach symptoms, neurosensorial symptoms, musculoskeletal symptoms, skin allergy symptoms and urinary symptoms) and a total score (sum of all subscales). Each item was rated on a five-point scale (0–4).

The Positive and Negative Affect Schedule (PANAS)[13] consists of two 10-item mood scales and provides measures of positive affect (PA) and negative affect (NA). Each item assesses, on a five-point scale (from 1: ‘very slightly or not at all’, to 5: ‘very much’), the intensity with which the emotion is felt.

The EuroQoL Visual Analogue Scale (EQ-VAS)[14] test is a quantitative measure of health status (HS). Each participant assessed his or her self-rated health on a vertical, visual analogue scale with 100 points with the endpoints being labelled: ‘Best imaginable health state’ (100) and ‘Worst imaginable health state’ (0).

Data analyses

To compare both groups for demographic factors and NA, PA, SP, SR and HS, we used t-tests for independent samples: Levene's test was used to assess the equality of variances. Previously, using the Kolmogorov–Smirnov test, we found that all measures followed a normal distribution. The analysis was completed with Cohen's d. In the FM group, we first used a Pearson correlation between somatic symptoms groups, SR and SP. Later, partial correlation analyses between somatic symptoms, SR and SP (controlling for age, years of study, PA, NA and HS) were conducted. Lastly, according to the correlations obtained, a multiple linear regression analysis (stepwise) was used. The statistical package spss 17 (SPSS Inc., Chicago, IL, USA) was used for the analyses.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Author Contributions
  8. References

Table 1 presents demographic data and scores in NA, PA, SR, SP and EQ-VAS of both groups. The two groups, patients and controls, were matched for age and for years of education. Patients with FM had higher NA scores than controls. PA was higher in controls than patients. Controls had higher SR scores than FM patients. In the HS, controls had higher scores than FM patients.

Table 1. Demographic data and differences between groups on different tests
 

FM

Mean (SD)

HC

Mean (SD)

t-scoreCohen's d
  1. *< 0.05; **< 0.01. FM, fibromyalgia; HC, healthy controls; PA, positive affect; NA, negative affect; SP, sensitivity to punishment; SR, sensitivity to reward; EQ-VAS, EuroQoL Visual Analogue Scale.

Age (years)52.59 (4.62)55.11 (5.88)−1.20−0.47
Years of study9.82 (2.76)9.00 (2.10)0.810.33
PA22.53 (8.82)30.30 (5.10)−2.53*−1.07
NA30.18 (10.23)20.30 (6.65)2.72*1.14
SP17.29 (5.96)13.70 (4.52)1.640.67
SR4.35 (1.65)7.10 (3.87)−2.58*−0.92
EQ-VAS36.00 (20.14)73.00 (15.91)−4.91**−2.03

Relationship between SR and somatic symptoms in FM group

In the FM group, significant correlations between the SR and different somatic symptoms groups were found. The significant correlations between SR and somatic symptoms are detailed in Table 2. Controlling for age, years of education, PA, NA and HS, only the SR/musculoskeletal symptoms correlation remained significant (see Table 2).

Table 2. Significant correlations between sensitivity to reward (SR) and somatic symptoms groups in FM patients
 ISRSSSMESSASUSTS
  1. *< 0.05; **< 0.01. IS, immunological symptoms; MES, musculoskeletal symptoms; ns, non-significant; RS, respiratory symptoms; SAS, skin allergy symptoms; SS, stomach symptoms; TS, total score of symptoms; US, urinary symptoms; PA, positive affect; NA, negative affect; HS, health status.

Bilateral pearson's correlations
SR−0.50*−0.51*−0.58*−0.67**−0.51*−0.57*−0.60*
Partial correlations (controlling for age, years of study, PA, NA and HS)
SRnsnsns−0.72*nsnsns

All variables were entered into a multiple linear regression analysis to determine which contributed independently to the prediction of musculoskeletal symptoms. In this analysis, with musculoskeletal symptoms as a dependant variable, only SR was entered as a predictor in the first step, giving an adjusted r2 of 0.423 (F(1, 18) = 12.01, = 0.004). The remaining variables were excluded. In the FM group, SR predicted 42.3% of the variance in musculoskeletal symptoms.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Author Contributions
  8. References

Patients with FM displayed a differential activity in the BAS of Gray's model compared with the control group. In this sample, the participants in the control group scored higher than FM patients in SR. The FM group was less sensitive to signals of reward than the control group. These results reflect the fact that the FM group displays BAS hypoactivity. BAS activity has been related to the development of positive affects and with impulsivity.[15, 16] In FM patients, BAS hypoactivity would reflect a poorer response to environmental incentives, resulting in a lesser number of exploratory and approach behaviors, and in a lesser tendency to present positive affective states (for example curiosity, desire, hope, euphoria or excitation). From a clinical perspective, the effect size obtained in SR between both groups could indicate that the BAS hypoactivity shown by FM patients is a clinically significant deficit.[17] Also, the large d statistic value for SR measures suggests that the small sample size does not affect the significance of the obtained results.[17] The results obtained indicate that FM patients present a level of BAS activity similar to patients with unipolar depression, where a lower level of BAS functioning compared to controls has been found.[18, 19] This is supported by the results obtained from the FM group in PA and NA levels, and offers new findings that show similarities between depression and FM in personality.

In relation to the second objective, we found that only BAS activity is related to self-reported somatic symptoms in FM. Controlling for different variables, the results obtained indicated that an increased perception of musculoskeletal symptoms is associated with reduced BAS activity. The finding of SR as a significant unique predictor of musculoskeletal symptoms confirmed that BAS activity is linked with these symptoms. The activity of this system predicts the self-reported musculoskeletal symptoms levels in FM patients better than other psychological measures included in this study. This relationship could be partially explained by the neural basis of BAS activity. This activity, dependent on structures, is involved in pleasure, movement and sensory-motor control (structures such as dopaminergic fibres which rise from the substantia nigra and ventral tegmental areas and innervate the basal ganglia, talamic nucleus and the motor cortex, sensory-motor and prefrontal cortex)[15, 20] that are important in musculoskeletal functioning.

There are several limitations to the current study. The first is the small number of participants. The relatively small sample size warrants a cautious interpretation of these results and also justifies the statistical tests used. Second, this study only investigates BIS–BAS activity in women; it would need to include men, since gender is an important variable in the study of these neurobehavioral motivational systems.[11] Future research should overcome these two limitations and could also explore BAS activity in different groups of patients and in relatives of FM patients. The inclusion of others clinical groups (chronic pain or chronic fatigue syndrome, affective disorders, etc.) could allow more to be known about the activity of this system in FM patients. Furthermore, the measurement of BAS could be a candidate variable for study in relatives of FM patients, since in some recent studies which used psychobiological models of personality have found similar personality traits in FM patients and their relatives.[3]

In conclusion, our findings document significant BAS hypoactivity in FM patients and suggest that the activity of this psychobiological system is associated with, and can predict, the musculoskeletal symptoms level. Lastly, although this is a preliminary study, it is new and suggests the importance of BAS activity in FM; further, it opens a new field in FM research.

Author Contributions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Author Contributions
  8. References

J. A. Becerra-Garcia and M. J. Robles: contribution to conception and design, execution, analysis and interpretation of data; reading and approval of the final version.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Author Contributions
  8. References
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