Heightened sensitivity to reward and punishment in anorexia nervosa

Anorexia Nervosa (AN) is a severe, often persistent mental illness with the highest mortality rate among all the psychiatric disorders (1). AN is characterized by intense fear of gaining weight, food restriction and weight loss, body image distortion, and amenorrhea (2). Central to AN is the ego-syntonic nature of weight loss, as well as the high rate of treatment resistance and drop out (3). The underlying pathophysiology of AN is unknown. AN is frequently associated with co-morbid anxiety disorders that often predate the emergence of eating disorder (ED) pathology (4). Individuals with AN are consistently characterized as highly perfectionistic and controlling (5) and show temperament traits such as high harm avoidance (HA; shy, fearful, worrying behavior, tendency to avoid perceived punishment), and lower novelty seeking (NS; the desire to explore and approach potential rewards) (4, 6-9). These characteristics raise the question whether such behaviors in AN are primary or adaptive in order to tolerate and handle the ups and downs of failures and accomplishments in daily life. While speculative, AN individuals may have heightened emotional or physiological sensitivity to experiences that are associated with reward or punishment, and that the eating disorder and associated behaviors may in some way serve to mitigate these responses by the sense of control received. We hypothesized that individuals with AN might be overly sensitive to the saliency of punishing or rewarding stimuli, and they may act to minimize exposure to such cues. Reinforcement Sensitivity Theory (RST) (10) provides a framework that explores how differences in brain systems responsive to punishment and reward are reflected in individual personality (11-12). In the original theory, personality dimensions such as anxiety and impulsivity were thought to be controlled by two underlying neural systems: the behavioral activation system, specifically responsive to rewarding stimuli resulting in approach behavior, and the behavioral inhibition system, responsive to aversive stimuli, or punishment, leading to inhibition of behavior (11-12). Conditioned and unconditioned stimuli activate the behavior activation and inhibition system. In the most recent revision of RST, the original behavioral inhibition system has been further divided into the fight-flight-freeze system (FFFS) and the behavioral inhibition-anxiety system. RST suggests that the FFFS responds to all potentially aversive stimuli, replacing the role of the original behavioral inhibition concept, whereas the revised behavioral inhibition-anxiety system, instead, resolves approach versus avoidance of a stimulus when there is a conflict and activation of both the FFFS and behavior activation system (11, 13). Based on this revised model, personality characteristics related to impulsivity, anxiety, and fear are independently mediated by the behavioral activation system, behavioral inhibition-anxiety, and FFFS systems respectively (11). Under the RST framework, individuals with altered sensitivities in these three systems may have an increased risk for psychological illness and distress (11), and research has shown that individuals with elevated FFFS are prone to phobia and panic, people with elevations of the behavioral activation system are prone to addictive behavior, and those with a heightened behavioral inhibition system activity in general may have an increased risk of anxiety disorders (13). Two self-report measures exist that were designed specifically to assess reinforcement sensitivity: The Behavioral Inhibition Scale/Behavioral Activation Scale (BIS/BAS) (14) and the Sensitivity to Punishment/Sensitivity to Reward Questionnaire (SPSRQ) (15). Although the BIS/BAS has been applied the most frequently in behavioral, psychophysiological and neuro-imaging studies, some have criticized the scale’s approach towards measuring “generalized sensitivity to reward and punishment, while Gray’s theory deals with sensitivity to specific cues” (15-17). In response to that criticism, the SPSRQ was developed to test behavior inhibition and activation systems employing questions related to very specific cues and situations. Just recently, the use of the SPSRQ has been validated for the use in eating disorder populations (18) supporting the assessment of reward sensitivity in AN using this questionnaire. While aiming to test the behavioral inhibition and behavioral activation systems, the two questionnaires differ with respect to questionnaire design and item presentation. Although there is clinical evidence of altered reward and punishment sensitivity in individuals with eating disorders, only a handful of studies have investigated the role of reinforcement sensitivity in ED populations using these measures. One group, using the BIS/BAS and SPSRQ, (18) reported that women with AN and bulimia nervosa (BN) have similar levels of behavioral inhibition reactivity; however, purging-type AN (AN-P) and BN had significantly higher levels of behavioral activation compared to restricting-type AN (AN-R), suggesting that BN and AN-P are more prone to act impulsively and approach potentially rewarding activities. That study did not include a control group, however. Another study, using only the BIS/BAS, reported higher levels of behavioral inhibition in AN-R than AN-P or controls, and lower levels of fun seeking (an aspect of behavioral activation related to the willingness to seek out potential rewards) and total behavioral activation (19). Two studies in female high school and college students using the BIS/BAS showed that heightened sensitivity to both punishment as well as reward predicted dysfunctional eating as assessed by the Eating Disorder Inventory, which suggested a possible link between Reinforcement Sensitivity and maladaptive eating behavior (20-21). The present study is the first to compare the SPSRQ between clinically diagnosed AN participants and healthy control women (CW). In addition, study participants completed the BIS/BAS questionnaire and measures of eating disorder symptomatology. Based on our clinical observations, and in line with the work by Loxton and Dawe, we hypothesized that AN would report increased sensitivity to both punishment and reward, as well as higher levels of behavioral inhibition and behavioral activation compared to controls (20-21). Such findings could suggest the presence of a biologic vulnerability underlying the ego syntonic, over-controlling, anxious and avoidant behavior often observed in AN.