MIT were showing on Horizon how they can activate areas of a mouse brain using light beams. That’s fine if you have optical fibres going into the brain. I have always considered that being able to stimulate and read and individual cells in the brain is the main key to immortality – it allows you to make a copy outside and migrate you thoughts and memories across until that becomes your main mind platform, then your brain doesn’t matter. Combining the ideas, if you have some sort of photo active cell as per the MIT group, and you can create the light using addressing of photorealism near those cells, then injecting addressable photo-diodes that can be IP addressed should allow you to interact with brain cells without needing optical fibres. You’d just need a radio link.
We can’t reasonably expect to inject one photo-diode for each brain cell, but we could make all the brain cells photo-sensitive using viruses to carry the genes, or electro-sensitive. Doesn’t matter which. Once every cell is sensitised, we can impose local structure using self organisation techniques and use that as mapping for signalling. Again this could use viruses to introduce the genes needed. This will allow each cell to be mapped relative to each of its neighbours and a full map of the brain made, with the ability to have two-way comms with each individual cell. Once we have that, the brain can signal two way to an external replica, in which the processing can be far faster, the storage far more secure and long-lived, emotional control far superior, and the sensing better. As you migrate your mind gradually onto the superior platform, your brain matters less and less, till one day when it dies, you will barely notice any drop in your mental function.