Humans, but not animals, perceive the thermal grill illusion as painful

Conditioned pain modulation dampens the thermal grill illusion

“…While the painfulness of the TGI has been questioned (Fruhstorfer et al., ; Bach et al., ), our results are in agreement with those of many others showing that interlacing warm and cool bars are capable of producing pain (Craig and Bushnell, ; Craig et al., ; Bouhassira et al., ; Leung et al., ; Defrin et al., ; Kern et al., ,b; Li et al., ; Boettger et al., , , ; Lindstedt et al., ,b). Three subjects (17%) did not, however, report any TGI pain during the Control run, confirming previous findings of some TGI‐insensitive individuals (Bouhassira et al., ; Kern et al., ,b; Boettger et al., ). Two of these subjects did report ‘burning’ and ‘stinging’ and the third reported ‘sharp’, suggesting that the TGI may still be unpleasant, if not painful, for these individuals.…”

“…Although many researchers have found that the TGI is painful to a majority of participants, others have debated the painfulness of the TGI and the involvement of the nociceptive system in generating the illusion (Fruhstorfer et al., ; Bach et al., ). Furthermore, a recent study reported that the TGI is not painful in cats (Boettger et al., ), calling into question the translatability of Craig and Bushnell's () physiological findings.…”