Illusory cold desensitizes touch

Abstract

In Jack Londons To Build a Fire, the doomed protagonist notes that "the tremendous cold had already driven the life out of his fingers... dead fingers could neither touch nor clutch". Indeed, our hands are numbed when exposed to cold, a desensitization process traditionally attributed to biophysical and physiological effects on mechanoreceptor and afferent responses1. Yet, perception is not based solely on sensory inputs and often reflects prior beliefs and expectations2. Accordingly, the mere experience of coldness, given its association with tactile desensitization, conceivably modulates touch independent of physical effects. We dissociated the physical and subjective influences of cooling on touch by leveraging the Thermal Referral Illusion3-7, in which cooling of the index and ring fingers induces an illusory perception of coldness that is referred to the middle finger which did not experience local cooling. We found that both veridical and illusory cold elevated tactile detection thresholds. Threshold shifts scaled with subjective ratings of cold intensity which varied with thermal adaptation. Thermal referral induction did not result in changes to skin temperature, ruling out indirect physical effects on the tested finger. To account for cold effects on touch, we implemented a computational model incorporating both physical and subjective factors by simulating changes in tactile afferent spiking activity8 and modulation of decision computations, respectively. The model reproduced empirical cooling effects on afferent responses9 and recapitulated psychophysical detection patterns. Our results reveal that subjective thermal perception contributes to cold-induced attenuation of touch, highlighting how multimodal experiences and expectations shape somatosensation.