Think of the brain as an extremely sophisticated analog computer. Fundamentally, it is composed of discrete units that function as processing nodes and that communicate with electrical impulses. All of this occurs at a subtler level than what we are used to with our simple technology so we are poorly equipped to analyze or even describe such constructs. However, it seems that once we attain sufficiently advanced technology we will be able to emulate and recreate this, in exactitude, in any substrate that supports analog computation.
( Of course with some limitations of design due to the speed of light and so on. The major caveat is assuming the nature is entirely physical and within 3+1 space-time, otherwise it would makes things vastly more complicated! In fact intractably complicated in 3+1 space-time ! )
The trouble with current efforts is that we try to impose a viewpoint derived from digital computation, i.e. from binary logic coupled with digital electrical circuits, on to what is clearly not running on a series of 1’s and 0’s. This defaulting of viewpoints is understandable and natural to almost everyone who was first exposed to computing machines after the introduction of von Neumann architecture, the predominant paradigm since the 1940’s, which is to say everyone younger than 90.
There is however no fundamental reason why computers made of silicon have to run on digital logic. Just as carbon based brains clearly support viable analog computation but are not fundamentally prohibited from digital signals. And there is no reason whatsoever that we need to remain constrained to digital computation in our future constructs.
We certainly weren’t in the several billion years preceding von Neumann’s, admittedly quite genius, design. In fact he even proposed an alternative that closely resembles what we would understand today as a relatively modern computer based on analog circuits!
And since we are on that topic, we don’t even necessarily need silicon based computers in the future. Other computational futures are perfectly possible! And carbon based computation works perfectly fine! (Though not as efficient in some tasks) Perhaps some future maverick will simply start making general purpose computers out of brains!
From the latest research reports it appears that one of the simplest brains, that of the zebra fish, has been fully simulated, albeit on a digital computer. Once the building blocks are understood, it is only a few more steps to simulating the evolution of the brain. Of course there are many millions of generations of evolution separating humans from the zebra fish, but that is a difference in proportion, not in kind. Even a network of intermediate brains, like that of squids, could be very useful and is theoretically possible.
( Caveat: Unless you believe in the idea(s) that only humans have souls, or some other intangible ‘essence’, that is not found in any other organism. In which case an even more sophisticated future maverick might propose working backwards from a human brain, with some obvious moral/ethical/spiritual/etc. concerns that need solving. )
In any case, the future is wide open to more advanced forms of computation than we can even dream of presently. Although I do not believe a return to analog computation is predestined, all signs point to us, or our descendants, emulating the brain to overcome some of the limits of our current paradigm that the most advanced research has already discovered. If realized, the consequences for all subsequent societies and derivative technologies will be profound.