PT  - JOURNAL ARTICLE
AU  - Björn Horing
AU  - Christian Sprenger
AU  - Christian Büchel
TI  - The parietal operculum preferentially encodes heat pain and not salience
AID  - 10.1101/581504
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 581504
4099  - http://biorxiv.org/content/early/2019/03/18/581504.short
4100  - http://biorxiv.org/content/early/2019/03/18/581504.full
AB  - Substantial controversy exists as to which part of brain activity is genuinely attributable to pain-related percepts, and which activity is due to general aspects of sensory stimulation, such as its salience. The challenge posed by this question rests largely in the fact that pain is per se highly salient, a characteristic which therefore has to be matched by potential control conditions. Here, we used a unique combination of functional magnetic resonance imaging, behavioral and autonomic measures to address this longstanding debate in pain research.Subjects rated perceived intensity in a sequence alternating between heat and sound stimuli. Neuronal activity was monitored using fMRI. Either modality was presented in six different intensities, three of which lay above the pain threshold (for heat) or the unpleasantness threshold (for sound). We performed our analysis on 26 volunteers in which psychophysiological responses (as per skin conductance responses) did not differ between the two stimulus modalities. Having thus ascertained a comparable amount of stimulus salience, we analyzed pain-related stimulus response functions, and contrasted them with those of the salience-matched acoustic control condition. Furthermore, analysis of fMRI data was performed on the brain surface to circumvent blurring issues stemming from the close proximity of several regions of interest located in heavily folded cortical areas. We focused our analyses on insular and periinsular regions which are strongly involved in processing of painful stimuli. We employed an axiomatic approach to determine areas showing higher activation in painful compared to non-painful heat, and at the same time showing a steeper stimulus response function for painful heat as compared to unpleasant acoustic stimuli. Intriguingly, an area in the posterior parietal operculum emerged whose response showed a pain preference, and where we can unequivocally exclude salience as explanation.This result has important implications for the interpretation of functional imaging findings in pain research, as it clearly demonstrates that there are areas whose pain-related activity is not due to general stimulus characteristics such as salience. Conversely, several areas did not conform to the formulated axioms to rule out general factors as explanations.