The researchers also found that electrical activity in these neurons responded instantly to light but decayed slowly in the dark. “Patients tell us it takes between one and five seconds for the light to make their pain worse, but it can take between five minutes to an hour for the pain to get better or to go away,” Dr. Burstein noted. “If the neurons we studied have anything to do with it, their activation should explain some of the latencies.”
Tracing also showed that the RGCs’ axons made both axodendritic and axosomatic connections with the dura-sensitive/light-sensitive neurons.
Finally, the researchers mapped these neurons’ axonal projections and found that they terminated in multiple cortical regions, including the primary somatosensory cortex, the visual cortex, the retrosplenial agranular cortex, the parietal association cortex, and the primary and secondary motor cortexes.
The somatosensory cortex terminations were expected, but the visual cortex terminations were more surprising and may put the light-migraine association “in the larger framework of how, in migraine, there are changes in visual perception,” said Dr. Burstein.
He added that the retrosplenial agranular cortex plays a role in short-term memory and that the parietal association cortex plays a role in spatial positioning—two more functions that are affected by migraine.
—Jack Baney