Abstract
Different pain types may be encoded in different brain circuits. Here, we examine similarities and differences in brain processing of visceral and somatic pain. We analyze data from seven fMRI studies (N = 165) and five types of pain and discomfort (esophageal, gastric, and rectal distension, cutaneous thermal stimulation, and vulvar pressure) to establish and validate generalizable pain representations. We first evaluate an established multivariate brain measure, the Neurologic Pain Signature (NPS), as a common nociceptive pain system across pain types. Then, we develop a multivariate classifier to distinguish visceral from somatic pain. The NPS responds robustly in 98% of participants across pain types, correlates with perceived intensity of visceral pain and discomfort, and shows specificity to pain when compared with cognitive and affective conditions from twelve additional studies (N = 180). Pre-defined signatures for non-pain negative affect do not respond to visceral pain. The visceral versus the somatic classifier reliably distinguishes somatic (thermal) from visceral (rectal) stimulation in both cross-validation and independent cohorts. Other pain types reflect mixtures of somatic and visceral patterns. These results validate the NPS as measuring a common core nociceptive pain system across pain types, and provide a new classifier for visceral versus somatic pain.
Highlights
Different pain types may be encoded in different brain circuits
Neurologic Pain Signature (NPS) expression in the four visceral pain/discomfort studies is shown in Fig. 1a, with the highest response in the esophageal pain study (Study 5)
Because the studies used to examine commonalities between somatic and visceral pain in the analyses reported above differ in terms of scanning hardware, pulse sequences, participant demographics, and experimental designs, we conducted a separate validation to evaluate whether the NPS can reliably discriminate individual brain responses to painful stimuli from nonpainful control manipulations across a sample of independent studies, with 6 studies manipulating pain and 12 control studies involving either manipulations of cognitive control or negative emotion
Summary
Different pain types may be encoded in different brain circuits. Here, we examine similarities and differences in brain processing of visceral and somatic pain. Pain is a primary force motivating human behavior, learning, and neuroplasticity It is defined primarily as an aversive experience[1] that arises from its signal value as an indicator of current or future bodily harm[2]. Despite the relevance of this knowledge gap, only a few studies in small samples of healthy controls have compared visceral and somatic pain directly using functional brain imaging. These studies have yielded mixed findings, including similarities as well as differential responses in somatosensory, cingulate, insular, and prefrontal cortices[10,11,12,13,14] and in subcortical regions, including hippocampus and dorsal pons[10]
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