These 11-year-old conjoined twins, Krista and Tatiana Hogan, are joined at the head, and, not only that, share part of their brains. As The Walrus reports (in a somewhat hyperventilating article), they each have a brain, but there’s a neural bridge between the thalamus of each brain (the part of the brain that relays sensory signals and is important in consciousness). This apparently makes them share each other’s sensations, so that what one sees or tastes is at least partly shared with the other. When one body is tickled, the other twin laughs. There’s even a shared mental connection—some sharing of thoughts, and we can’t conceive of what that’s like. Nobody else in the world, nor any pair of twins, has this kind of cerebral connection.
They weren’t expected to survive, and even if they did they were expected to be in a vegetative state. They’ve defied those expectations, but aren’t in fantastic health: one has heart problems because she pumps blood to her twin’s brain, and they also have epilepsy and slowed intellectual development. Still, they’re doing pretty well given the situation.
Here’s a 45-minute CBC documentary made when the twins were seven: an absolutely fascinating look at a neurological anomaly, but also at the resilience of two girls in the face of an inoperable condition. They’ll be head to head for life. (If one of them dies, the other will follow shortly). It’s also a one-off opportunity to study the transfer of experience, but of course if you were the parent, or the girls, would you want them probed and examined by a bunch of scientists?
As The Walrus says, this raises questions about what “self” means, but that’s a bit of an exaggeration. The real question is “how is one’s sense of being a ‘self’ modified when your brain is connected to another brain?”
This is a great documentary, and if you have a spare 45 minutes, I recommend that you watch it. Seriously. Some might think they’d be grossed out by this, but give it a try. I was heartened and fascinated, and there’s a fair bit of science in there, too.