The nature of the mind and consciousness is a puzzle which many people have looked at. Today the physicalist philosophy of mind seems to be dominant, but there are many dissenting voices. In this article I present and argument which suggests that there may be more to our minds than just a computer program. I have to say that I don't take this argument particularly seriously myself, but I feel that it's an interesting addition to the debate about just what our minds are made of.

To be a warm blooded creature is expensive in terms of energy. You can't just lumber around and eat when you feel like it - you need some way of making sure you get enough food to maintain your body temperature. Animals have evolved different ways of dealing with this. Sheep have a complex multi-chambered stomach so that they can eat relatively indigestible food such as grass. Primates (such as us) have taken a different option - they have bigger brains so that they can do better in finding highly nutritious food. But the the thing is that any new organs are also going to require energy. For instance, although our brains comprise about 2% of our body mass, they use about 20% of the energy we obtain from our food. (Don't believe your science teachers when they say that thinking doesn't count as work in the physical sense).

A lot of work has been done to see if there is a minimum energy requirement for a computational task. The answer seems to be that there isn't - as long as the computer can be made to operate in a reversible manner. Such a computer would need to operate using minimal amounts of energy and it would need to be very well isolated from its environment(note that we are not talking about quantum computation here though). So far we have not got anywhere near being able to do this, or even approach the optimum for a non-reversible computer which is about 3×10^-21Joules per logical operation at room temperature. A typical computer processor uses about 3×10^-8J per operation, while the brain does much better, taking 3×10^-15J per synapse operation.

So what advantage does a neuronic brain have that a DNA brain does not? Well one possible answer is consciousness. It might be that to be conscious isn't just about running a certain program, that something extra is required, and that that something might be present in neurons but not in DNA. This point of view isn't dualism as such - that would imply a separate world of consciousness. Rather it says that consciousness might be related to the physical makeup of our brains, and cannot be simulated by a computer. Several people have put forward similar ideas, such as John Searle. A similar view (but one which Searle disagrees with) is that of Roger Penrose, who has given an account of how consciousness may be due to quantum effects in the microtubules in our brains.

But, you may ask, isn't the evolutionary function of the brain a computational one? Well maybe not. Consider the example given by Donald Griffin of the caddis fly larva which builds itself a protective case. If part of this is damaged then it repairs the damaged part. Now identifying the part that needs repairing may seem like a trivial task to us, but its the sort of thing that it's difficult to write a computer program to do. You would need to monitor various inputs and have a decision procedure which then activated the right behaviour to mend the damaged part. It would seem much easier if the insect has such a thing as consciousness, so that it would know that there was a problem and do what was necessary to fix it. Of course many people would say that this consciousness is just another program running in the background, but I say that it might not be. One day we'll be able to tell whether or not such behaviour is adequately explained by the computational properties of the brain, but we certainly haven't reached that point yet - the often made claim that 'the physical world is causally closed' isn't really based on evidence.