In one of his works, Adi Shankara asks a question way beyond his time-
'When you close your eyes and imagine things, how are those images formed? An image needs light. What is the source of light for imagination?'

It is highly likely the Buddhist Vijnanavadins had already examined this question. They were obsessed with the problem of mental images.
If this question can be properly answered, we may have a key to unravel the mind-brain enigma: One of the greatest mysteries of the universe.

Even real life things you see with your eyes are mere images projected in the occipital lobe. You are actually 'seeing' with the back of your head!
What about mental images? Is some 'light' involved? Are neurons producing it? How? What is the physical link of neuron & thought?

Most theories such as those of Penrose and Hameroff are largely discredited. The missing link between physics and neuroscience remains elusive. The question of 'light' maybe-just maybe- the chink in the fortress of the mind-brain enigma.