The Pain Imaging Revolution: Advancing Pain Into the 21st Century

Abstract

The great advances in brain imaging techniques over the last few decades have determined a shift in our understanding of chronic pain conditions and opened the door for new opportunities to develop better diagnoses and perhaps better drug treatments. Neuroimaging has helped shape the concept of chronic pain from a disease affecting mainly the somatosensory system, to a condition in which emotional, cognitive and modulatory areas of the brain are affected, in addition to degenerative processes. All these contribute to the development and maintenance of pain symptoms and co-morbid features including alterations in anxiety, depression and cognitive processes. In this paper we review the current understanding of the brain changes in chronic pain and the developments made possible by the use of various brain imaging techniques. We also discuss the possible applications of brain imaging to developing a “pain phenotype” that could aid in diagnostic and treatment choices of chronic pain conditions.

Nociception and autonomic nervous system

“…In other words, nociceptive input would generate a conscious percept of pain through the activity it elicits in the network constituting the ''pain matrix'', and, hence, measuring the activity within this network would constitute a direct and objective measure of the actual experience of pain [22]. The pain matrix is subdivided into medial and lateral pain systems; this distinction, which is based on the projection sites from medial or lateral thalamic structures to the cortex, is probably an oversimplification of the networks involved but it is a useful means for grouping brain regions that appear to have similar roles in pain perception [12].…”

A multisensory investigation of the functional significance of the “pain matrix”

“…It is interesting to note that this possibility had already been put forward by a number of early studies (e.g., Bancaud et al, 1953;Carmon et al, 1976;Stowell, 1984) but has often been dismissed by recent studies, which have considered that because the stimulus elicits a sensation of pain, it is reasonable to assume that the elicited brain responses are at least partially pain-specific (e.g., Avenanti et al, 2005;Boly et al, 2008;Borsook et al, 2010;Brooks and Tracey, 2005;Ingvar and Hsieg, 1999;Jones, 1998;Ploghaus, 1999;Stern et al, 2006;Talbot et al, 1991;Whyte, 2008;Wiech et al, 2008).…”

“…However, pain was viewed as only one of many possible perceptual outputs of this "neuromatrix", which was thus not considered to be pain-specific (Melzack, 2005). Only in later studies the label "pain" was added to the term "neuromatrix", leading to the current concept of a "pain matrix" (e.g., Avenanti et al, 2005;Boly et al, 2008;Borsook et al, 2010;Brooks and Tracey, 2005;Ingvar, 1999;Jones, 1998;Ploghaus et al, 1999;Talbot et al, 1991;Whyte, 2008). This relabeling introduced a fundamental deviation from the original concept, as it implied that the pattern of brain responses elicited by nociceptive stimuli reflects a pain-specific network and, hence, that functional neuroimaging could be used to "delineate the functional anatomy of different aspects of pain" (Ingvar, 1999).…”

[18F]-fluorodeoxyglucose positron emission tomography of the cat brain: A feasibility study to investigate osteoarthritis-associated pain

“…The use of functional imaging of the CNS to assess pain in animals is a recent and growing field (Borsook and Becerra, 2011). The major advantages of these techniques are the possibility to collect objective measures of pain, to compare data across several species, to target specific central mechanisms, and to perform study designs with repeated data (Borsook et al, 2010;Borsook and Becerra, 2011;Davis and Moayedi, 2013).…”