171 Psychopathological and neurobiological overlap between anorexia nervosa and self-injurious behavior automatically negatively reinforced by the reduction of negative affect and potentially positively reinforced by an increase in positive affect (in case of dietary restriction this could be an increase in positive mood, control and accomplishment) and are thus maintained by reinforcement and habituation. Both NSSI and EDs symptoms have been reported by patients as forms of self-punishment. In conclusion, there seem to be psychopathological links between NSSI and AN in emotion dysregulation, (maladaptive) coping behavior, and reinforcement or reward (56). AN and NSSI: neurobiological overlap The neurobiological evidence on AN and NSSI summarized above, suggests that processes related to reward are essential in their overlap. As described above, NSSI induces opioid related reward to compensate for lower levels of endogenous opioids (39, 42). If reduced sensitivity of endorphin receptors and/or low levels of endogenous opioids are typical for patients engaging in NSSI, NSSI and also anorectic/eating disordered behavior in these patients might be a way to self-stimulate the endogenous opioid system. The endogenous opioid system and the reward system are closely linked, since opioid modulates DA pathways resulting in an increased DA release in for example the striatum. Furthermore, opioids are thought to be involved in the emotional value of reward, but also in modulating appetite and energy metabolism (17). One class of opioids, beta-endorphin, is released during stress as well as during positive experiences and causes an euphoric rush and a reduced pain perception. NSSI, but also other impulsive behaviors like binge-eating, results in a release of beta-endorphin and its rewarding rush (39, 42, 45). Interestingly, as a consequence of malnutrition, beta-endorphin levels are reduced in AN-patients (17). NSSI, but possibly also the self-destructive eating disorder related behavior itself, in these patients could therefore be a way to self-stimulate and mobilize the last reserves of the endogenous opioid system (42). From this perspective, the state of malnutrition in AN-patients stimulates the engagement in self-destructive or other radical behavior. Besides NSSI, also bingeeating, food restriction and excessive exercising are ways to gain such an endorphin rush and thus to stimulate the reward system (39, 42, 57). In this way, self-destructive behavior is providing a short-term rewarding relief of the typical negative emotional state in AN-patients. Thereby, endogenous opioid dysfunctioning seems an important explanation for the neurobiological association between NSSI and AN. Moreover, distilling the evidence summarized above on the neurobiology of AN and NSSI, both are linked to reward-related processes like DA dysregulation, serotonergic functioning and abnormal activation in the cortico-striatal neurocircuit.
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