New Developments in the Understanding and Management of Persistent Pain

Herta Flor PhD

Disclosures

Curr Opin Psychiatry. 2012;25(2):109-113. 

In This Article

Learning Processes in Chronic Pain

Implicit learning processes involve sensitization, operant and respondent conditioning, as well as priming and social learning. Sensitization refers to a nonassociative learning process wherein the repeated or extended application of a stimulus leads to an increased response that can be described on the physiological level, usually referred to as 'central sensitization', or the psychological level, usually referred to as 'perceptual sensitization'. Its counterpart is the process of habituation, wherein repeated stimulation leads to a reduction of the response to the stimulus, which can also be described on the physiological or behavioral level.

In a number of chronic pain syndromes, perceptual sensitization has been observed, which is also accompanied by enhanced activation in the central nervous system. For example, in patients with fibromyalgia syndrome or patients with chronic back pain, enhanced perception of tonic painful stimuli or repetitive painful stimulation has been observed.[3•]

Operant conditioning is another mainly implicit learning mechanism that can lead to chronicity. The operant view proposes that acute 'pain behavior' such as limping may come under the control of external contingencies of reinforcement and thus develop into a chronic pain problem. Pain behavior may be directly positively reinforced, maintained by the escape from noxious stimulation or deficient reinforcement of 'well behavior' (e.g. activity, working). The pain behavior originally elicited by somatic factors may thus come to occur, totally or in part, in response to reinforcing environmental events. Not only observable pain behaviors but also verbal expressions of pain and physiological variables may come under the control of the contingencies of reinforcement. Becker et al.[4••] showed that increases or decreases of pain perception can serve as implicit reinforcers and that this operant conditioning of sensitization or habituation is differentially altered in patients with fibromyalgia with or without irritable bowel syndrome.

As the experience of pain is a very important biological stimulus, it is immediately evident that respondent (Pavlovian) conditioning might play an important role when pain is repeatedly experienced, as is the case in the transition from acute to chronic pain. In the typical classical conditioning paradigm, a previously neutral variable (later the conditioned stimulus), when paired with a biologically significant stimulus (unconditioned stimulus), comes to elicit a conditioned response that resembles the response to the unconditioned stimulus, the unconditioned response. For example, if a certain movement has been associated with pain, just thinking about the movement may already elicit fear and muscle tension (previously elicited by pain) and may then motivate avoidance behaviors. Once an acute pain problem exists, fear of motor activities that the patient expects to result in pain may develop and motivate avoidance of activity. Nonoccurrence of pain is a powerful reinforcer for reduction of activity and thus the original respondent conditioning may be followed by an operant learning process, whereby the nociceptive stimuli and the associated responses need no longer be present for the avoidance behavior to occur. In acute pain states it may be useful to reduce movement, and consequently avoid pain, to accelerate the healing process. Pain related to sustained muscle contractions might, however, also be conceptualized as a unconditioned stimulus in the case wherein no acute injury was present and sympathetic activation and tension increases might be viewed as unconditioned responses that might elicit more pain, and conditioning might proceed in the same fashion as outlined above. Thus, although the original association between pain and pain-related stimuli results in anxiety regarding these stimuli, with time the expectation of pain related to activity may lead to avoidance of adaptive behaviors even if the nociceptive stimuli and the related sympathetic activation are no longer present. Fear of pain and activity may become conditioned to an expanding number of situations. Avoided activities may involve simple motor behaviors, but also work, leisure and sexual activity. In addition to the avoidance learning, pain may be exacerbated and maintained in these encounters with potentially pain-increasing situations due to the anxiety-related sympathetic activation and muscle tension increases that may occur in anticipation of pain and also as a consequence of pain. Thus, psychological factors may directly affect nociceptive stimulation and need not be viewed as only reactions to pain. Aversive emotional conditioning with painful stimuli as unconditioned stimulus has been shown to be exaggerated in chronic back pain patients, as well as patients with tension type headache,[5••,6] and leads to increased muscle tension responses. Meulders et al.[7••] showed that movement can be a conditioned stimulus that can be associatedwith pain and itself elicit fear ofmovement, an aversivemotivational state and avoidance of movement. Social learning or modeling related to viewing pain in others may be an additional important learning process that can also play a role in chronicity. Although empathy for pain is a prerequisite for social learning, social learning goes beyond emotional involvement in others' pain, especially when the pain of another person is experienced as if it were one's own pain.[8•] This might itself be an important stimulus for pain chronicity.

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