You Are Two
Your brain is two brains. Two hemispheres, each doing half the work of being you. Half your vision goes to each, and half your movement directed by each. Right controls left, and left controls right. Your two brains coordinate through a wire of nerves, but this wire can be cut, and was, for a time, used as an epilepsy treatment. After the cut, people seemed the same, though their brain was split in twain.
Except, some post-split patients described that while selecting their morning outfit with the right hand, the left might come along to disagree. Actually, the left hand might quite often disagree, which these split-brain patients found frustrating. What's happening? To investigate, remember, the right brain sees and controls one half, while the left brain controls and sees the other. But only the left brain can speak.
"Hello." Because that's where the speech center is located. The right brain, without this, is mute. In normal brains, this doesn't matter because each half communicates across the wire with the other. But, split-brains can't, and thus, you can show just the right brain a word, ask the person: "What did you see?" and you'll hear: "Nothing." Because the left speaking brain saw nothing.
Meanwhile, the right brain will use its hand to pick the object out of a pile hidden from the left brain. This is deeply creepy. Ask, "Why are you holding the object?" and the speaking left brain will make up a plausible sounding, but totally wrong, reason. "I always wanted to learn how to solve one of these." The left brain isn't lying; it's just doing what brains do: creating a story that explains its past actions to its current self, a behavior that does rather cast doubt onto the notion of free will (but that's a story for another time).
Creating reasons for why it does things is just something left brains do. It happens in normal, healthy humans all the time, and if you think about it closely, you know you've done this. Back to experiments. Give the right brain an object, ask the person "What's in your hand?" and they won't be able to say. "I'm not holding anything." And when asked to draw, a split-brain can draw two separate objects simultaneously, with each hand, in a way unsplit-brains find challenging.
These experiments on split-brain patients are deeply unsettling because they really point in the direction of a mute separate... intelligence... Something... Living in the skull. You can even ask questions of a split-brain and get disagreement on the answer. So, if your brain is split, who is the 'you' in this situation? From the outside, it's tempting to think of the part of the brain that's speaking as the person, but something is hearing and answering questions.
And, though the right brain can't speak, it does understand faces, which the left brain can't. If this is you, you don't know who your friends and family are in a crowd. This act of cutting exposes two minds in one head, and the talking mind doesn't know there's someone else in the house. The left brain can describe the situation it's in, but nonetheless will constantly be surprised by the right brain's actions and explain them away.
There's a question to be asked here: Why, after separation, does the right brain not totally freak out, but instead play along helpfully, answering questions, and listening to the left brain's dumb stories about what's happening. - It's the best pony... I don't know. - Speculation time...
But, one answer is the cutting doesn't make the right brain a separate... intelligence... consciousness... person? But rather it has always been. In normal people, perhaps the right brain rose up as a companion without a choice. Feeling at first somewhat equal partners, but then, as speech develops that it can't participate in, that increasingly becomes the central point of life, it resigns to mutely coordinate with the left brain.
At this moment, in your normal head, there are two of you watching this video: one having a 'mind = blown' moment, and the other mentally rolling its eye at the obviousness of it all. In split-brains, the right doesn't freak out because not a whole lot has really changed. You might not agree, and maybe arguing right now at why it can't be possible, exactly as we would expect talking left brain to do.
Speculation aside, split-brain patients show, at the very least, that in the mind, there is a separate... something that can hear and understand and respond, given the right circumstances. Your brain isn't entirely yours. Who is you? You is two.
[soft music] [Grey's voice morphing into Kurzgesagt's voice] But we can go deeper. You are many. [Kurzgesagt's voice] The pile of meat that's your body is made up of trillions of tiny individuals that have a life of their own. [Kurzgesagt's voice] So, at which point do the many become one? [Kurzgesagt's voice] What makes lots of tiny things you? [Kurzgesagt's voice] Click here to go to our channel and watch the next part.
[Grey's voice] Seriously. If you haven't checked out Kurzgesagt, then you don't know what you're missing. Kurgaset? Kurtzgaset? I never know.