This is hidden brain.
I'm Shankar Vedantam in Anthony Dorr's wonderful novel, all the light we cannot see, a radio host poses a question to an audience of children.
The brain is locked in total darkness.
He says 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?
It's not just about light, of course.
The world inside our heads is full of sound, movement, and sensation.
It is suffused with feelings and emotion.
Imagine for a moment that your brain was a person locked inside your head.
How does this person create a world so rich, so varied, and so beautiful when she is permanently trapped within the cage of your skull?
Most of us have a ready answer.
The brain has many messengers that bring it information signals stream in from our eyes and ears and skin.
The brain takes in all these signals.
And like a film editor splicing together a movie, assembles our perceptions of the world.
But in recent years, some scientists have come to believe that this is not what actually happens.
The light we see and the sounds we hear are not really comprised of signals from the outside world.
Instead, they are mostly creations of the mind itself.
When I first heard this idea, it made little sense to me.