The location and time variation of this bioluminescence is very interesting. It does seem to match the location and temporal phase of nasal NO production.

http://www.jiaci.org/issu...

NO is frequently detected by chemiluminescence from reaction with O3. Is there enough O3 in ambient air to produce a small number of photons by this mechanism?

Low temperature does reduce nasal NO production. Lower NO (as from NOS inhibition) increases cortisol production (probably by differential regulation of cytochrome P450 enzymes), so an inverse correlation is not unexpected.

There is considerable NO/NOx chemistry going on in the mouth. Salivary glands concentrate nitrate ~10x over plasma levels and commensal bacteria on the tongue reduce it to nitrite. It is interesting that the two high metabolic rate tissues in the field of view (heart and brain) did not seem to be specific sources of light.

There seems to be a variation in background light emission that might be consistent with a volume source of photons from exhaled NO. That background also seems to vary in phase with the direct photoemission from the subject. (but images F and G seem to look suspiciously identical, perhaps a mislabeling?)

This is very interesting work which will <i>shed light</i> ;) on free radical reactions occurring in vivo. I look forward to seeing more results.