Thermosensation as a novel method to probe interoception and its relationship with other interoceptive modalities

Interoception includes signals originating both from inside the body and from its surface, the skin. Here, we focused on the perception of temperature, a crucial modality for the maintenance of homeostasis. We used a classic (static) thermal detection task and developed a new dynamic thermal matching task, in which participants have to match a previously perceived moving thermal stimulus on the skin to a range of colder or warmer stimuli, presented in increasing or decreasing order. We investigated both hairy (forearm) and non-hairy (palm) skin, in keeping with previous tactile studies targeting the potential involvement of C-tactile fibres, which are part of an afferent homeostatic system found mainly on hairy skin. We also aimed at investigating the relationship between performance on the two thermal tasks and on three other tasks in different interoceptive sub-modalities: cardiac perception, affective touch, and pain detection. We found a significantly more accurate perception of dynamic temperature on hairy compared to non-hairy skin overall, particularly when the temperature was decreasing. Static perception of cooling was also superior on hairy skin and was related to dynamic temperature and pain only on non-hairy skin. Thus, our results suggest that hairy skin may have higher thermosensitivity than non-hairy skin and that dynamic thermosensation might offer a promising avenue to investigate thermosensation as a skin-based interoceptive submodality. Critically, we did not find any other significant relationship in performance among the four interoceptive modalities examined, which indicates independent processing and that interoception might be best quantified using a battery of tests.