We used to think this was not possible. When I was an undergraduate we were taught that you were born with all your braincells, and that if you damage a braincell then that’s it. We now know that’s not true. There can be some regrowth. You can get recovery in the brain by rewiring, you can get some new braincells growing, and there’s a lot of interest now in how we can promote that.
There would be a great number of difficulties if you were to try and transplant actual braincells, simply because of what they are: a neuron is a great hairy thing, a really unusual-looking cell, with this cell nucleus and then these long axons, or nerve fibres, that connect across the brain: these can be really long, like quite a few centimetres. To transplant it, it might have to be somehow threaded right through the brain, which obviously presents significant logistical problems as a structure.
So instead, the main interest right now comes from stem cell research: a stem cell can come from anywhere in your body – a stem cell is a stem cell is a stem cell – and you have to tell it what it’s going to be, you have to signal “you’re in a liver”, “you’re in the skin”, “you’re in the hypothalamus” and it will grow accordingly. This is mainly a clinical interest, it’s actual treatments that are being researched, so people are treating things like Parkinson’s Disease with stem cells, and in fact a colleague of mine is being treated for spinal problems with stem cells at the moment.
“Hypothetically, if you're introducing a chunk of someone else’s brain into yours then you'd carry over their knowledge with it.”
The point there is that you’re not putting in a neuron – you’re not “transplanting a brain cell” – you’re putting in a stem cell that’s going to become a neuron. So it’s not coming over with any baggage from any baggage from any previous owners, because it was never a neuron in someone’s brain, it was a stem cell from somewhere else. You’re certainly not importing information with the brain cell.
If you were bringing in brain cells from somewhere else – and I’m speaking completely hypothetically here – it’s highly unlikely one neuron would make a difference, because information is never stored in just one. But if you were introducing a chunk of someone else’s brain into your brain – and again, this is totally hypothetical, because this is not being done, and we don’t know how it would be done – then yes, you can imagine that you would actually carry over knowledge with it.
There isn’t anything else storing information like that in the body except for brain tissue, so that’s where it’s located: we certainly know that if you lose an area of the brain, you can lose a chunk of information, so we can only assume that if you moved that chunk, the information could be transferred along with the tissue. How we’d actually do this, how it would be connected, how it would talk to the new brain, how the brain would know what this new piece was: all that is unknown – certainly there’d have to be a process of learning to access anything that was there – but in theory you could access things that the donor brain had learned.