Mini-brains inside the brain

Naming brain regions is a vague and haphazard process. For example, ‘cortex’ just means ‘bit of brain’, and this can range from the neocortex, which is the entire outer layer of your brain, to the dorsolateral prefrontal cortex which is a coin sized bit near the front of your head. And the same ‘cortex’ can be called different things. So the orbitofrontal cortex is the same region as the ventromedial prefrontal cortex. This is true for heaps of brain regions. The basal ganglia is also called the striatum. And so on. And, to make matters worse, as I’ve said elswhere:

If you’re ever in the habit of reading neuroimaging papers and have time on your hands, look up the coordinates of any brain region. You’ll notice that the same region’s coordinates differ from paper to paper. Very annoying¹.

What I’m trying to emphasise here, if my article on the subject doesn’t convince you, is that talking about brain regions is usually silly. If we’re not talking about massive regions that are highly correlated with most things people do, we’re talking about small regions that are under no obligation to be the same region that someone else was talking about, even if they share the same name.

But some regions do really seem to do some stuff.

Maybe the most famous are the Broca’s and Wernicke’s area. Usually, these regions sit side-by-side at the outermost middle part on the dominant side of your brain. So if you’re right-handed, these’ll probably be on the left. Left-handed, and they’re more likely to be on the right. They do language: the Broca’s area seems to concentrate on language production, and the Wernicke’s area seems to be more interested in language comprehension. So you wouldn’t be surprised to learn that these live right underneath where the brain plans all its motor activity—movement. Language is a fundamentally a motor task (you move your mouth/hands), so put it where the rest of these things are put together.

This isn’t that interesting though. What’s interesting is the fact that most brain regions have a representative on both sides—one side of the brain for one side of the body. Your left hand has a region on the right side, and your right hand has a region on the left. But these areas almost always only appear on one side of peoples’ heads.

No one can give me a very good explanation for why this is. Usually it’s just ‘something something evolution’, but the something something doesn’t really make you sit up straight. The most compelling, to me, is the idea that maybe language production is so inherently central (i.e. it comes out of your mouth) that it doesn’t make sense to have a region on the opposite side of the head as well. The brain found a spot at the bottom of the part of the brain where you plan motor movements, started building your speech production abilities in, then realised it’d be overcomplicating things to duplicate this on the other side of the head as well.

But because it’s one of the very few truly one-sided brain regions, you can explore some interesting features of the brain. The wildest of these comes from some of the work Roger Sperry did with his ‘split-brain’ patients. Split-brain patients are patients who’ve had the corpus callosum severed. This structure is largely connective tissue, binding the two hemispheres of the brain together, allowing them to communicate with each other and coordinate the two halves of your body. If you’re epileptic, you suffer from what’s essentially an electrical fault—some part of your brain starts shorting out, and it causes you to seize. The more the electrical disruption spreads, the worse your seizure. If you have really bad seizures, they might spread over your entire brain. So, cut the brain in half, by severing the corpus callosum, and the electrical disruption can’t spread past the hemisphere it started in. A serious solution to a more serious problem.

The most famous of Sperry’s patients, ‘Joe’, had his corpus callosum split. And after the surgery, Sperry and his colleagues notices that Joe’s brain seemed to have developed some very strange kind of independence.

Remember that most regions of the brain are bi-lateral. You have a region of the brain on the right side that receives visual information from the left eye, and another region of the brain on the left side that receives visual information from the right eye. Because Joe was right-handed, his language areas lived on the left side of the brain.

They’d show Joe different things in different eyes. So, maybe they’d show him an apple at the right eye, which piped into the side of the brain where his language areas lived. They’d also show a bicycle to the left eye, which piped into the opposite side of the brain. Then they’d ask Joe what he saw, and Joe’d easily report the presence of an apple, but wouldn’t mention the bicycle. But ask him to look down and point to the card that matched what he saw with his left hand (controlled by the side opposite the language areas, which the bicycle-seeing eye fed into), and he’d point at the card with a bicycle on it.

Because his brain was split, it’s almost like there were two versions of him in there. One that could report out loud what he saw through the eye that fed the language side of the brain, and one that could only pick up or draw what he saw through the other eye.

And it gets weirder. Ask Joe to explain why he’d chosen a card with a bicycle on it, and he’d talk about how he used to cycle to the orchard to pick up apples as a kid, or something. Some rationalisation for what he chose based on what the language-sided eye saw, and not the thing his handed-eye saw.

Sam Harris, most famously, writes about this somewhere, using it to talk about how our perception of our self is an illusion. Here, we have two ‘entities’, two ‘consciousnesses’, made apparent by the severing of Joe’s brain. And we can only ‘speak’ to one of them. Of course, given we’re still struggling to explain consciousness, this feels like an awfully confident assertion.

But certainly it points to a much greater capacity for and complexity of agency than we usually consider. We aren’t just the ‘self’ perched behind the eyes, looking out and controlling things. There is a society of processes in our brain and body, all working together to get the job done. And the ‘self’ isn’t always able to tell you who’s pulling the strings. At least, it might try, but there’s no particular reason to believe that it knows what it’s talking about.

And as a final point, it’s worth noting that the Broca’s and Werneke’s areas aren’t the only language production regions. There’s an entire network responsible for the processing and production of language, and most of this lives on both sides of the brain. It’s just these two, the bits responsible for getting it out of the mouth, that live on the dominant side. This is why there’s no real weight to the myth that some people are ‘left-brained’ and analytical and some people are ‘right-brained’ and intuitive. Your analytical stuff lives all over your head, as does your emotional stuff, and if it was reliant on the location of your language regions, everyone would be analytically-brained because they appear on the dominant side for almost everyone. If you’re particularly analytical, or particularly intuitive, it has nothing to do with brain ‘sided-ness’. You don’t need to make up brain things to justify how you like to live your life.

Our language areas produce some of the most obvious of our behaviour, but that’s not quite the same thing as the most important. The strange isolation of these two language areas highlight that. The way you think is made up of a wonderously complicated network of processes, some you can speak to, but many more that you can’t. And that’s alright. We’re animals first, and even with a brain cut in half, we’re doing just fine.