"To determine whether there is a colour preference to migraine-type photophobia, we assessed the effects of white and four different colours of light on: (i) proportion of migraine patients who reported changes in headache intensity; (ii) magnitude of change in pain rating; (iii) number of patients who report change in sensory perception other than headache intensity; and (iv) spread of headache from its original site...
At the highest intensity (100 cd·m −2 ), nearly 80% of the patients demonstrated an intensification of headache; this was true for all colours except the green, which affected half that proportion of patients. Unexpectedly, exposure to green light reduced pain intensity in ∼20% of the patients...
To explain the psychophysical findings, we sought to determine whether electrical signal generated by the retina in response to green light differed from those generated by the other colours... Collectively, these ERGs suggest that activation of cone-mediated (but not rod) retinal pathways can play a role in the weak ‘photophobic’ effects of green and strong ‘photophobic’ effects of white, blue and red."
There is a weird point in here about excluding red light from the thalamus-stimulation experiments, so I'm not in love with the conclusions they gathered there and I didn't pull that part.
I wonder why green light would be treated differently by the brain - or, put another way, why other wavelengths of light might be translated into pain signals.
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