Cognition in the Chronic Pain Experience: Preclinical Insights

Abstract

Acutely, pain is protective. It promotes escape from, and future avoidance of, noxious stimuli through strong and often lifetime associative memories. However, with persistent acute pain or when pain becomes chronic, these memories can promote negative emotions and poor decisions often associated with deleterious behaviors. In this review, we discuss how preclinical studies can provide insights into the relationship between cognition and chronic pain. We also discuss the concept of pain as a cognitive disorder and new strategies for treating chronic pain that emphasize inhibiting the formation of pain memories or promoting 'forgetting' of established pain memories.

Keywords: chronic pain; extinction; memory; pain theories.

Figure 1:. Progression of Theories of Pain.

(A) In the ‘Treatise on Man’ Descartes proposed the first pain pathway [119]. In this, sensory stimuli activate hollow tubules, opening a gate in the brain, allowing the animal spirits to enter the tubules and activate the muscles to move them away from danger. (B) The ‘Tripartite Model’ of Melzack and Casey in the 1960s [1] includes the sensory/discriminative, motivational/affective and cognitive/evaluative dimensions of pain. This epiphany in the understanding of pain, led to a resurgence in interest in the motivational/affective experience, something that had long been neglected after the initial definition of pain as the antithesis of pleasure by ancient Greek philosophers. (C) Craig proposed pain as a “homeostatic emotion”, maintaining the integrity of the body [120]. Acutely in response to pain, autonomic processes protect homeostasis but higher-order motivated behaviors, such as resting injured areas, are also needed to promote healing and aid full restoration of homeostasis. (D) These ideas were expanded further by Fields in the motivation-decision model of pain [19]. In this a subconscious decision is made on what to attend to, based on a cost-benefit analysis. ‘ON’ and ‘OFF’ cells in the rostral ventral medulla (RVM) have been shown to mediate pain according to whether it is to be acted on or not.

Figure 2:

Example studies of cognitive impairments in chronic pain patients.