For example, a seven-year-old autistic child Nadia had exceptional artistic skills. She was quite retarded mentally, could barely talk, yet she could produce the most amazing drawings of horses and roosters and other animals. A horse drawn by Nadia would almost leap out at you from the canvas. Contrast this with the lifeless, two-dimensional, tadpole-like sketches drawn by most normal eight or nine-year-olds - or even normal adults.

So we have another paradox. How can this retarded child produce a drawing that is so incredibly beautiful? The answer, I maintain, is the principle of isolation.

In Nadia perhaps many or even most of her brain modules are damaged because of her autism, but there is a spared island of cortical tissue in the right parietal. So her brain spontaneously allocates all her attentional resources to the one module that's still functioning, her right parietal. Now it turns out that the right parietal is the part of your brain that's concerned with your sense of artistic proportion. We know this because when it's damaged in stroke, for example, in an adult, you lose your artistic sense. You produce drawings that are often excessively detailed but lack the vital essence of the picture you're trying to depict. You lose your sense of artistic proportion. Conversely, since everything else is damaged in Nadia's brain she allocates all her attention to this brain module - so she has a hyper-functioning art module in her brain. Hence the beautiful renderings of horses and roosters.

Another example, equally striking. Dr Miller, University of California, has studied patients who start developing rapidly progressing dementia in middle age, a form of dementia called the fronto-temporal dementia, affecting frontal lobes and temporal lobes, but sparing the parietal lobe. And guess what happens. These patients suddenly start producing the most amazingly beautiful paintings and drawings - not all of them but some of them - even though they had never had any artistic talent before the onset of their dementia. Again, it's the isolation principle at work. With all other modules in the brain not working the patient develops a hyper-functioning right parietal. There are even reports from Alan Snyder in Australia that you can temporarily paralyze parts of the brain in normal volunteers - all of us less gifted people here. Imagine just zapping bits of your brain and unleashing hidden talents. If that happens, it will truly be a brave new world.

We don't have time to talk about all my other laws in detail. But I'll just mention the last law on my list - and in many ways the most important, yet the most elusive: Visual Metaphor. You all know what a metaphor is in literature as when you say it's the East and Juliet is the sun. But you can do the same thing in visual art - both in Western art and in Indian art. For example, when you look at the Chola bronze of the dancing Shiva or Nataraja with multiple arms you are not meant to take the multiple arms literally or call it a multi-armed monstrosity like the Victorian art critic, Sir George Birdwood, did. Funnily enough he didn't think that angels sprouting wings were monstrosities - although I can tell you as a medical man you can have multiple arms, but wings on scapulae are anatomically impossible!

The multiple arms are meant to symbolize multiple divine attributes of God and the ring of fire that Nataraja dances in - indeed his dance itself - is a metaphor of the dance of the Cosmos and of the cyclical nature of creation and destruction, an idea championed by the late Fred Hoyle. Most great works or art - be it Western or Indian - are pregnant with metaphor and have many layers of meaning.

Everyone knows that metaphors are important yet we have no idea why. Why not just say: "Juliet is radiant and warm" instead of saying: "Juliet is the sun"? What is the neural basis for metaphor? We don't know but I'll have a stab at this question next week in my Oxford lecture on synesthesia.

With that I conclude my lecture on Neuro-aesthetics. Have we understood the neural basis of art? Of course not. We have barely scratched the surface. But I hope the "laws of art" I've discussed might give you some hints about the general form of a future theory of art.

The solution to the problem of aesthetics, I believe, lies in a more thorough understanding of the connections between the 30 visual centres in your brain and the emotional limbic structures. And once we have achieved a clear understanding of these connections, we will be closer to bridging the huge gulf that separates C.P. Snow's two cultures - science on the one hand and Arts, philosophy and humanities on the other.

We could be at the dawning of a new age where specialisation becomes old-fashioned and a new 21st century version of the Renaissance man is born.

In the 19th century, the Victorian scientist Francis Galton, who was a cousin of Charles Darwin, noticed something very peculiar. He found that certain people in the normal population who were otherwise perfectly normal had a certain peculiarity and that is every time they heard a specific tone, they would experience a specific colour. For example, C sharp might be red, F sharp might be blue, another tone might be indigo. And this curious mingling of the senses was called synesthesia. Some of these people also see colours when they see numbers. Every time they see a black and white number like the number five printed on a white page, or a white five on a black page for that matter, they would see it tinged red so five might be red, six would be green, seven would be indigo, eight would be yellow and so on and so forth. Galton also pointed out this condition runs in families and more recently Simon Baron Cohen in Cambridge has confirmed this, that it does indeed run in families.

Now I think it's fair to say that even though people have known about synesthesia for over a hundred years, it's been by and large recorded as a curiosity by mainstream neuroscience and psychology but what I'd like to do today in fact is suggest that anomalies can be extremely important in science. If you know which anomaly to pick, you can completely change the direction of your research and generate what you would call scientific revolutions. But first let's look at the most common explanations that have been proposed to account for synesthesia and in fact there are four of these. The first explanation is the most obvious and that is that they're just crazy! Now the second explanation is maybe they're just acid junkies or pot heads, they've just been on drugs. Now this is not an entirely inappropriate criticism because synesthesia is more common among people who use LSD but to me that makes it more interesting, not less interesting. Why should some chemicals cause synesthesia, if indeed they do?

The third idea is that maybe these people are just remembering childhood memories. For example maybe they were playing with refrigerator magnets and five was red and six was blue and seven was green, and for some reason they're stuck with these memories but this never made much sense to me because why would it then run in families? You'd have to say they're passing the same magnets down, or the propensity to play with magnets runs in families or something like that. Anyway it didn't make much sense but it's something you have to bear in mind. The fourth explanation is more subtle and it invokes sensory metaphors. If you look at our ordinary language, it's replete with synesthetic metaphors, cross-sensory metaphors such as for example if you said cheddar cheese is sharp. Well cheese isn't sharp, you can take a piece of cheese and rub it on your skin, it's actually soft. So why do you say it's sharp? Well you say oh no no, what I mean is it tastes sharp, it's a metaphor. But this is circular - why do you use a tactile adjective, touch you know sharp, for a taste sensation?