[ELI5] Why aren’t brain transplants possible?


If there is a brain dead patient and a person with multiple failing organs, why is it not possible to transfer the brain to from patient to patient? I understand there are many ethical reasons to give somebody another’s body, but if both had given consent then would it be possible and if not why?

In: 15

The brain is connected to the rest of the body via a bunch of nerves. Each one of these nerves goes to a specific part of your body. It’s also not the same for everybody.

So imagine you have a big data cable with 1000 wires inside of it. You cut it and try to connect it to a different cable with 1100 wires. None of these wires are labeled or color coded. None of them lead to the same place. Trying to get them to match up and make it work is basically impossible.

If we had the ability to do this, we would first use it to help people who have accidents or birth defects where they end up paralyzed. Those damaged or severed connectors in their body we aren’t able to reconnect, let alone an entire nervous system

To piggyback on the other comment, if you had technology sufficient enough to properly contact all of those neural pathways, then you have technology sufficient enough to just reverse brain death.

Dude, there was a huge documentary about this back in the late 80’s if I recall…

“the man with two brains” it was called. Absolutely worth the watch.

Something that hasn’t been mentioned yet about the scale of reconnection is that even if we could conceivably plug a new brain into an existing nervous system “correctly” it would also have to be done incredibly fast. For example we can keep organs like lungs, kidneys and livers alive for between 9-12 hours outside a body. One of the most complex transplants currently performed is the lungs which can take up to 12 hours to transplant. So with a brain you’re looking at a longer procedure and more tissue death

There are three major problems (and probably more less major but still difficult ones).

1. As others have mentioned we do not have the capability yet of reattaching the nerves that connect the brain to the rest of the body. We can’t even reconnect the nerves in on person to their own same set of nerves, say by a spinal cord injury.

2. In order to do a transplant you need to keep the organ alive once it’s removed from the original body. There is a very limited amount of time to do this and for the brain it would be even harder because it has some very strict requirements in terms of blood and oxygen before it shuts down.

3. Our bodies are designed to fight foreign biological things inside us. The more foreign it is, the more they fight. When transplanting organs you try and find someone who mat he’s various important aspects about you as much as possible. The closer you can get (usually a close family member) the less chance the body will reject the organ. Even then you have to take medication for the rest of your life to weaken your immune system to keep rejection from happening. The brain is a super complex organ meaning it’s going to be a LOT harder to fight rejection AND you are very unlikely to find a patient who is a close enough match to serve as the donor body.

Perhaps someday we will be able to address all of these problems, but it’s more likely we’ll be able to replace or repair the persons own damaged body rather than transplanting their brain.