Nociception
Pain has been in this wiki from the first ingest and has never had a page, for a revealing reason: it enters almost every source as an example — of a lamina I modality, of an insular function, of a channel that failed to correlate with the heart — and never as the thing being measured. Wilzok et al. (2023) is the first source here to put pinpricks on a forearm and treat the resulting reports as interoceptive data, which forces the question the wiki had been able to leave open.
The scope question
Two positions, both defended in print, with no adjudication.
Broad inclusion. Craig (2002) pulled pain inside interoception as part of the general widening that also brought in temperature, itch, hunger, thirst and air hunger — on the grounds that all of them arrive via the lamina I spinothalamocortical pathway to the insula, and all report on the physiological condition of the tissue. On this view a pinprick and a stomach cramp are the same kind of signal about different tissue. Wilzok et al. adopt it explicitly, arguing that all forms of nociception share “their shared objective of maintaining bodily homeostasis.”
Narrow inclusion. Ceunen, Vlaeyen & Van Diest (2016), On the origin of interoception, restrict interoception to visceral nociception, leaving cutaneous and musculoskeletal pain outside as somatosensation. Critchley & Garfinkel (2017) note the disagreement without settling it.
The wiki cannot resolve this and should not pretend to. What it can do is record where the choice bites.
Where the choice bites
It changes what Wilzok’s cross-modal correlation means. The r = 0.57 between respiroceptive and nociceptive discrepancy is a within-interoception finding on the broad view and a interoception-to-somatosensation finding on the narrow one. Those are different results with different consequences for is-interoception-domain-general, and the paper reports one number.
It changes the direction of the existing nulls. Ferentzi et al. (2018) and Crucianelli et al. (2022) both included nociceptive measures among the channels that failed to correlate with cardiac sensitivity. On the broad view those are interoceptive nulls that count against domain generality. On the narrow view they are partly nulls between interoception and something else — which is unsurprising and much weaker evidence. The same studies argue differently depending on a definition neither of them states. That is worth holding onto: the domain-generality debate has been quietly assuming the broad view in order to count its own evidence.
It changes what the lesion data say. Jones, Ward & Critchley (2010) report Starr’s two patients rating noxious stimuli as more intense with no insular activation — pain awareness surviving insula destruction entirely. If pain is interoceptive, that is a serious problem for the insula-as-interoceptive-cortex model. If pain is somatosensory, it is a fact about a different system and the model is untouched. The wiki has been treating it as the former.
What pain adds that no other channel offers
Three properties, and they are why nociception keeps being reached for as an experimental channel even by people unsure it qualifies.
- It is gradable with physical units. PinPricks come in calibrated millinewtons; thermal stimuli in degrees. Almost no interoceptive channel can be dosed this precisely — the gastric channel has no psychophysical instrument at all, and the cardiac channel’s stimulus is whatever the heart happens to be doing.
- It is unambiguously aversive, so it supports the perturbation logic sahib-khalsa argues for without pharmacology.
- It has a large independent literature on prediction. The pain field established decades ago that people overpredict intense pain and that underpredicted pain hurts more (Rachman & Arntz 1991; Arntz 1996) — a body of work on interoceptive expectation that the interoception literature largely does not cite. Wilzok et al.’s finding that the same asymmetry appears for inspiratory loading is a small bridge across that gap, and suggests the pain field’s prediction literature may be about aversive interoceptive states generally.
That third point is the most useful thing on this page. The wiki’s interoceptive-inference and predictive-coding pages theorize about biased priors on bodily states; the pain literature has been measuring one for thirty years.
Status
Open, and this page exists to stop the wiki drifting into an unexamined default. The working convention here is broad inclusion with the caveat flagged at the point of use — which is what the study and method pages do — rather than a silent commitment either way. See interoception-exteroception-boundary, where this is one instance of a general problem.