Pain or nociception? Subjective experience mediates the effects of acute noxious heat on autonomic responses - corrected and republished

Abstract

Nociception reliably elicits an autonomic nervous system (ANS) response. Because pain and ANS circuitry interact on multiple spinal, subcortical, and cortical levels, it remains unclear whether autonomic responses are simply a reflexive product of noxious stimulation regardless of how stimulation is consciously perceived or whether the experience of pain mediates ANS responses to noxious stimulation. To test these alternative predictions, we examined the relative contribution of noxious stimulation and individual pain experience to ANS responses in healthy volunteers who underwent 1 or 2 pain assessment tasks. Participants received 8 seconds of thermal stimulation of varied temperatures and judged pain intensity on every trial. Skin conductance responses and pupil dilation responses to stimulation served as measures of the heat-evoked autonomic response. We used multilevel modelling to examine trial-by-trial relationships between heat, pain, and ANS response. Although both pain and noxious heat stimulation predicted skin conductance response and pupil dilation response in separate analyses, the individual pain experience statistically mediated effects of noxious heat on both outcomes. Furthermore, moderated mediation revealed that evidence for this process was stronger when stimulation was perceived as painful compared with when stimulation was perceived as nonpainful, although this difference emerged late, in the 4-second period after thermal stimulation. These findings suggest that pain appraisal regulates the heat-evoked autonomic response to noxious stimulation, documenting the flexibility of the autonomic pain response to adjust to perceived or actual changes in environmental affordances above and beyond nociceptive input.

Confidence in subjective pain is predicted by reaction time during decision making

“…We fit an initial linear regression between temperature and pain rating from the first 3 heat stimulations. The fit was iteratively updated and used to predict the remaining 21 temperatures consistent with prior work using this approach (e.g., [40][41][42][43] ). Although all temperatures were estimated to evoke pain, some trials (M within-subjects = 3.96 trials) were rated as non-painful.…”

“…We only measured fixations during a three-second looking period while participants viewed the pain scale prior to recording responses. It is possible that fixations would be more variable during the heat stimulation period itself; however, we did not display the pain rating scale during this period to allow for pupil dilation analyses in a larger study assessing physiological responses of pain 43 . Furthermore, it is possible that participants may have disengaged from the task and behaviors were diminished during the three-second looking period, as this period preceded mouse presentation used for pain ratings.…”

“…Participants received monetary compensation for their time and for receiving painful stimulation. Pain reports and heat-evoked physiological responses from this sample were included as a subset of a larger sample in a previous publication 43 that did not evaluate confidence. Summary statistics were conducted on the full sample.…”

Infrared Thermography for Estimating Supraclavicular Skin Temperature and BAT Activity in Humans: A Systematic Review

“…Whether shorter times induce similar BAT 18 F‐FDG uptakes is unknown; the one study that did use a 10‐minute cold exposure did not employ a nuclear technique to measure BAT activation. Furthermore, the cooling technique used (applying cold to the hands) could have activated BAT via a side pathway rather than through the classical cold pathway . More studies are needed to determine which protocol is the most appropriate for activating human BAT .…”

“…Certainly, the lack of any changes in IRT‐measured SST when employing 5‐minute cooling times may reflect that such short cold stimuli are insufficient to induce BAT activation (it should be noted that the majority of studies did not report the temperature of other zones as controls). However, extremely long cooling protocols might activate BAT via pain rather than cold pathways . Basically, different cooling protocols could induce different responses, and the contribution of the tissues in nonshivering and shivering thermogenesis could be dissimilar.…”