Painful cold-heat segmental pulse stimulation provokes the thermal pain illusion

Abstract

Purpose/Aim

The thermal grill illusion is a paradoxical pain sensation induced by simultaneous exposure to spatially separated, non-painful, cold, and warm stimuli. This study aimed to determine whether paradoxical sensations are also evoked by simultaneous exposure to painful cold-heat stimuli and whether the mechanism involves modulation by segmental and extra-segmental spatial integration.

Materials and Methods

Sensory perceptions were triggered by simultaneous application of painful cold-heat pulse stimuli using a developed bedside tool equipped with quantitative thermal stimulator devices. Four conditions were investigated: (1) one device placed on the forearm (condition 1, control); (2) two devices placed on the forearm (condition 2, ipsilateral segmental integration); (3) two devices placed on the forearm and ipsilateral thigh (condition 3, extra-segmental integration); and (4) two devices placed bilaterally on the forearms (condition 4, contralateral segmental integration). The evoked perceptions of paradoxical heat sensation and the loss of cold or heat sensation were evaluated.

Results

The aforementioned phenomena were experienced by 11(35.4%), 3(9.7%), 3(9.7%), and 0(0.0%) subjects for conditions 1–4, respectively. Fisher's exact test revealed significant differences (p=.001) among the four conditions. However, Bonferroni post hoc analysis revealed significant differences only between conditions 1 and 4 (p=.005).

Conclusions

Simultaneous painful cold–heat pulse stimulation can induce paradoxical sensations similar to those shown for non-painful thermal (cold and heat) stimuli. They were predominantly evoked by ipsilateral integration. Paradoxical sensations have diagnostic value, and quantifying them using a simple bedside tool may be useful in the clinical setting.

Keywords:

• Painful thermal pulse stimulation
• paradoxical sensation
• thermal pain illusion

Acknowledgments

We thank the participants for their consent and cooperation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author (Yuka Oono) upon reasonable request.

Additional information

Funding

This work was supported by JSPS KAKENHI under grant numbers JP15K20975 and JP15K20972. The Center for Neuroplasticity and Pain (CNAP) is supported by the Danish National Research Foundation (DNRF121).