Persistent neuropathic pain influences persistence behavior in rats.

Persistent pain is a major health problem and is a primary reason that many people seek health care services.1,2 Persistent pain conditions are challenging to live with and are often associated with high levels of stress for the individual.3,4 These conditions are characterized by complex interactions between cognitive, emotional, and physiologic disturbances that bring about significant coping challenges for patients. Each of these disturbances requires that individuals exert effort toward regulating their behavior in multiple domains while enduring and subsequently managing the persistent pain condition.4 The successful management of persistent pain mediated by the trigeminal nerve is the goal of orofacial pain patients and clinicians alike. It is not surprising that persistent orofacial pain taxes personal resources and has been associated with self-regulatory deficits in patients. Self-regulation involves the capacity to exert control over cognition, emotions, and behaviors.5-7 It is defined as one's ability to alter his/her own responses by overriding one response in favor of a less common but more desired response.4,8 Self-regulation is also related to executive functioning, including the ability to make choices. Research in human populations indicates that performing an initial self-regulatory task may cause fatigue that results in poorer subsequent performance on executive tasks.9,10 Thus, self-regulatory fatigue and executive capacity covary inversely in a way that can lead to a potential downward spiral where repeated responses to demands leads to self-regulatory fatigue, which in turn reduces executive cognitive resources.4 This pattern increases the difficulty for an individual to meet further demands such as those associated with persistent intractable pain in structures mediated by the trigeminal nerve. Although self-regulation has been implicated as important in the management of persistent pain conditions, research outcomes show that persistent pain itself can interfere with the ability to self-regulate.11 In the one human study on pain and self-regulation found in the literature, patients with persistent pain conditions, ie, fibromyalgia and temporomandibular disorders, had less capacity to persist on a persistence task following an initial self-regulation task than persons without persistent pain.11 These findings suggest that the presence of persistent pain leaves one vulnerable to self-regulatory fatigue because of the significant demands required for coping with persistent pain. In the past, many researchers have argued that self-regulation occurs only in humans; however, a recent animal study has shown that it is possible to examine these effects in other species.12 In that study, dogs in a self-regulatory condition (ie, dogs commanded to sit and stay for a short period of time) performed worse on a persistence task (ie, attempting to retrieve food from a toy) than dogs that had not been required to self-regulate prior to exposure to the persistence task. These findings suggest that self-regulatory capacity may be a finite resource across species and is involved in guiding and directing a broad spectrum of behaviors. Although past research on self-regulation has been primarily conducted with human participants,13-15 it would be beneficial to study the effects of persistent pain on self-regulation in a rodent model. A rodent model of persistent pain allows for greater experimental control and fewer threats to internal validity. For example, in human populations with persistent pain, both physical and psychological comorbid conditions are common.16,17 Studying persistent pain conditions with animals in a controlled setting allows investigators to limit the variables affecting the relationship between persistent pain and self-regulation. Additionally, animal models allow for investigation of physiological pathways responsible for self-regulatory deficits as well as possible pharmacological treatments. The aims of the current study were to determine (1) whether self-regulation can be studied successfully in a rodent model and (2) whether persistent facial pain influences self-regulatory behavior. It was hypothesized that animals experiencing persistent neuropathic pain would perform more poorly on a persistence task that immediately followed an initial self-regulatory depletion task than naive animals that were not experiencing pain. Specifically, it was expected that as a result of increased fatigue following the self-regulation task, animals that underwent surgery to induce a chronic constriction injury of the infraorbital nerve (CCI-ION) would press a lever during the persistence task for a shorter period of time as well as a fewer number of times than naive animals.