What do we mean when we talk about "the brain"?
Easy, right? It's this:
Certainly, this is the image that comes to my mind.
But this is not an image of a brain. It's an image of a dead brain.
In a living brain, all kinds of interesting things are happening. Things we literally can't begin to imagine. Because these are hard to visualize, they can't enter the mental picture.
To picture the living brain as just a yellowy lump is like picturing Wikipedia as a disc. It's accurate as far as it goes, but it misses the whole point. You could download Wikipedia onto a BluRay disc, and then you could describe that disc as "Wikipedia" and you wouldn't be wrong, but Wikipedia is much more than a silver circle.
It doesn't help much that we know that there's more to the living brain than a yellowy lump. Yes, most of us know that the living brain is somehow responsible for thought, feeling, perception, and consciousness.
But we have no idea of how it does so, we don't have any feel for this relationship. We agree with the idea that brain = mind, but that's just an abstract equation. Just as most of us know that e=mc2, but only physicists understand it.
All this leads to philosophical problems. Wittgenstein wrote:
Look at a stone and imagine it having sensations. - One says to oneself: How could one so much as get the idea of ascribing a sensation to a thing? One might as well ascribe it to a number! - And now look at a wriggling fly and at once these difficulties vanish and pain seems able to get a foothold here.
What he meant is that we only feel that we can ascribe pain (or any "internal" mental state or event) to something which is behaving "externally".
Now in most cases, that's fine. Most inanimate objects really don't have mental states. But brains do. The brain, we feel, is inanimate; it's just a yellowy lump. By itself the brain is like Wittgenstein's stone - it seems.
So, we feel, the brain itself can't really have mental states, only walking, talking, behaving people can, like wriggling flies. Except we know on an abstract level that brains do have mental states; so we tie ourselves into philosophical knots about "brains" and "persons", asking whether a person is more or less or the same as a brain, and so on.
The whole problem could be removed, I think, if instead of a yellowy lump, we could picture the living brain in all its active complexity; if we could talk about "the brain", not as an inanimate object, but as the most animate thing in the world.
In the brain there are hundreds of billions of cells, and each one is a hive of movement - not visible to the naked eye or even to a microscope, but the movement of ions and neurotransmitters and ultimately information.
I think many philosophical puzzles would lose their edge if we could somehow get a feel for all that; if we could replace the accurate, but misleading, yellowy lump picture of "the brain" with one that captures the complexity and dynamism of the thing: a city, a hive of insects, a vast machine.