If a brain is exposed to an intermittent light are specific areas going to fire? If yes, which of them? Is there any experiment about this?
It is thought that there are no active optical receptors in the brain normally, its possible some effect might show up in the future, it would be minor at best.
Shining light into the brain is standard procedure in optogenetics experiments. A subpopulation of neurons is transformed to express an optical receptor to modulate genetic or signalling properties of the cell.
So the reason I say it would be small effect on a native brain is that these experiments do give good results and are run with controls which do not have the optical receptors added, which typically show no change in brain activity.
Image taken from the linked Wikipedia page and originally from Baratta et al..