Dual-use neural pathways: Warm thyme

My father has always described the taste of certain soups as "warm" -- it is, to him, the absolute best adjective he can come up with. Now we know why.

Certain herbs, when applied to the tongue or the skin, elicit a neural response that is the same as if the temperature had been raised. The neural pathways evoked by thyme, oregano, and cloves are (at least for some people) the same as those used in a thermal response. The soup really is "warm"!

I have tried this experiment with thyme flavor myself, and can sort of perceive the temperature effect, but it is not distinct enough to be certain. Probably I feel it because I know I am looking for it. Perhaps only some people have these dual-use pathways, or perhaps some people are more able to perceive the two effects.

I looked for a reference, but the clearest version seems to have been publised in Nature, to which I don't have online access. Here is an abstract that may be relevant:

Nat Neurosci. 2006 Apr 16; : 16617338

Oregano, thyme and clove-derived flavors and skin sensitizers activate specific TRP channels.

Haoxing Xu , Markus Delling , Janice C Jun , David E Clapham

Carvacrol, eugenol and thymol are major components of plants such as oregano, savory, clove and thyme. When applied to the tongue, these flavors elicit a warm sensation. They are also known to be skin sensitizers and allergens. The transient receptor potential channel (TRPV3) is a warm-sensitive Ca(2+)-permeable cation channel highly expressed in the skin, tongue and nose. Here we show that TRPV3 is strongly activated and sensitized by carvacrol, thymol and eugenol. Tongue and skin epithelial cells respond to carvacrol and eugenol with an increase in intracellular Ca(2+) levels. We also show that this TRPV3 activity is strongly potentiated by phospholipase C-linked, G protein-coupled receptor stimulation. In addition, carvacrol activates and rapidly desensitizes TRPA1, which may explain the pungency of oregano. Our results support a role for temperature-sensitive TRP channels in chemesthesis in oral and nasal epithelium and suggest that TRPV3 may be a molecular target of plant-derived skin sensitizers.