All the light we can not see

The brain is locked in total darkness, of course, children, says the voice. It floats in a clear liquid inside the skull, never in the light. And yet the world it constructs in the mind is full of light. It brims with color and movement. So how, children, does the brain, which lives without a spark of light, build for us a world full of light? 

– All The Light We Cannot See, Anthony Doerr