Subliminal (latent) processing of pain and its evolution to conscious awareness

Abstract

By unconscious or covert processing of pain we refer to nascent interactions that affect the eventual deliverance of pain awareness. Thus, internal processes (viz., repeated nociceptive events, inflammatory kindling, re-organization of brain networks, genetic) or external processes (viz., environment, socioeconomic levels, modulation of epigenetic status) contribute to enhancing or inhibiting the presentation of pain awareness. Here we put forward the notion that for many patients, ongoing sub-conscious changes in brain function are significant players in the eventual manifestation of chronic pain. In this review, we provide clinical examples of nascent or what we term pre-pain processes and the neurobiological mechanisms of how these changes may contribute to pain, but also potential opportunities to define the process for early therapeutic interventions.

Delineating conditions and subtypes in chronic pain using neuroimaging

“…Despite this, evidence suggests that a relatively high level of accuracy can be obtained in relation to healthy populations (approximately 70%–90%). Comparing results from the above investigations with those shown to contribute towards subliminal pain processing (see Ref. 8), it is interesting to note that only cortical structures are observed.…”

“…1) that report both cortical and subcortical structures as being active, as well as prior findings that implicate subcortical structures in pain processing. 8 Reasons for this may include low variability in subcortical volumes, inconsistent labeling of subcortical structures, and a lower relative contribution to pain symptoms in comparison with cortical structures. The precise nature of this will be the subject of future research.…”

“…It has been previously argued by our group that pain processing continues, even if it does not reach conscious awareness. 8 To this point, analysis of neuroimaging data would provide invaluable knowledge that could not be addressed using existing phenotypic evaluation criteria. However, the delineation of brain regions implicated in specific pain cohorts has received a paucity of attention because the pain-neuroimaging field first validates the ability to distinguish regions that are implicated in the elementary response to pain.…”

“…The concept of overlapping pain conditions and associated pain symptom reporting adds further complexity to the clinical diagnosis, which may be informed by brain imaging of pain-relevant brain networks that occur on a subliminal level. 8 For example, the insula is a region implicated in pain salience in patients with migraine whose structural morphology and functional activity are clinically related. 7 As well, subcortical brain structures including the amygdala, brainstem, and cerebellum are involved in the processing of emotional elements of a painful stimulus such as fear of pain condition.…”

Commentary on Higgins et al. (2020): How are chronic pain, psychological distress and opioid dependence related?

“…They argue that ‘… the emotional limbic brain plays a critical role in bridging nociception and pain perception, as well as in the transition from acute to chronic pain, leading to the generalization of the functional continuity between pain and negative moods’. Nociception turns into conscious acute pain when necessary to protect against further injury and to promote healing . Similarly, acute pain turns into chronic pain when threats to bodily and personal integrity have not resolved.…”