A novel method to selectively elicit cold sensations without touch

Background: Thermal and tactile stimuli are transduced by different receptor classes. However, mechano- and thermo-sensitive afferents interact at spinal and supraspinal levels. Yet, most studies on responses to cooling stimuli are confounded by mechanical contact, making these interactions difficult to isolate. Methods for precise control of non-mechanical thermal stimulations remain challenging, particularly in the cold range. New method: We developed a non-tactile, focal, temperature-controlled, multi-purpose cooling stimulator. This method controls the exposure of a target skin region to a dry-ice source. Using a thermal camera to monitor skin temperature, and adjusting the source-skin distance accordingly, we could deliver non-tactile cooling stimuli with customisable profiles, for studying different aspects of cold sensation. Results: To validate our method, we measured absolute and relative thresholds for cold sensation without mechanical contact in 13 human volunteer participants, using the method of limits. We found that the absolute cold detection threshold was 32.71 oC ± 0.88 oC. This corresponded to a threshold relative to each participant's baseline skin temperature of - 1.08 oC ± 0.37 oC. Comparisons with existing method: Our method allows cooling stimulation without the confound of mechanical contact, in a controllable and focal manner. Conclusions: We report a non-contact cooling stimulator and accompanying control system. We used this to measure cold thresholds in the absence of confounding touch. Our method enables more targeted studies of both cold sensory pathways, and of cold-touch interactions.