The brain is not a computer, of course. But wait. Computers are devices that process information…and that’s certainly what the brain does, right?

As an alert reader pointed out in my post on Roger Penrose, the English mathematician and philosopher, the problem here lies in the definition of “computer” or “computer-like”.

In one sense, saying that the brain is a computer is saying exactly nothing. That’s since the word “computer” refers to any device that “computes”—processes information. That includes everything from adding machines to quantum computers . Penrose may think the brain operates on quantum principles—so fine, it may be a quantum computer, but that’s still a computer. The only possibility for negating the assertion that the brain is a computer in this extremely general sense is to hold that the brain does not even “process information”. Perhaps it is doing something with information other than processing it, or perhaps it is processing something other than information as we know it. A more likely possibility is that it might be processing information but, at the same time, doing additional, important things that cannot be interpreted as processing information—such as being conscious. In that case, we would have to say the brain is only partially “like a computer.”

We also have to be aware of hidden agendas in defining these words. For some people, saying “the brain is not (like) a computer” is a kind of code for a belief in the human “spirit”, the absolute uniqueness of our “minds”, or the ineffability of existence. These people are simply making an exclamation of a particular variety of faith.

Personally, I believe that even consciousness is a form of information processing, and thus that the brain is a computer in the tautological sense. (Not that I think it’s a quantum computer.)

In that case, in what sense of the word “computer” does the brain fail to qualify? The narrowest sense is that of von Neumann, a stored program computer , one that computes a problem sequentially and deterministically from beginning to end. Even if we include parallel processing within the von Neumann paradigm, our “neural computer” does not fit within that framework. Most basically, it seems clear our brains involve no equivalent of a “program” or “stored data” in the von Neumann sense.

A broader sense is that of the Turing machine. This is the model that Eric Baum believes the brain works under, although in his details he often seems to have a von Neumannian focus. A Turing machine executes algorithms, and serves as a model for all modern computer hardware and software architectures.

If we limit ourselves to considering the synaptic architecture of the brain, we can say that it has Turing-like aspects, and its processing can be described as being algorithmic in nature, but it’s very unlike any Turing machine you’ve ever seen, with tens of thousands of dendrites converging on individual neurons, and neuronal plasticity involved in a type of learning at the level of the architecture of the “machine” itself.

But in other important regards the brain is almost certainly not a Turing machine. First, neural functioning involves chemical and hormonal levels which are fundamentally analog in nature; such analog behavior could be simulated by a digital computer, but never reproduced exactly. Second, the brain appears to be strongly specialized to deal with intrinsic temporal flow and temporal patterns.

In summary, we can say that the brain is a semi-analog, parallel, self-modifying, temporally-specalized device for processing information. Whether or not that’s a “computer”, we’ll leave up to the reader.

This entry was posted on Wednesday, May 11th, 2005 at 18:38 and is filed under computing. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.