Now, however, we then found this is not true of all synesthetes. All synesthetes are not made equal. We then ran into other synesthetes where it's not merely a number that evokes colour but even days of the week evoke colours. Monday is red, Tuesday is indigo, Wednesday is blue, months of the year evoke colour, December is yellow, January is red, February is indigo. No wonder people thought they were crazy! But remember, if you're a clinician you know when somebody sounds crazy it usually means you're not smart enough to figure it out. He isn't crazy. What do calendars, what do days of the week, months of the year and numbers have in common? What they all have in common is the abstract idea of sequence or ordinality. So what I am claiming is that's represented in the angular gyrus, higher up in the TPO junction, temporal parietal occipital junction in the vicinity of the angular gyrus, and guess what? The next colour area in the sequence is higher up in the general vicinity of the TPO junction, not far from the angular gyrus so what I'm arguing is - in these people the cross-wiring is higher up in the angular gyrus. Then you get a higher synesthete, so if the faulty gene is selectively expressed in the fusiform gyrus, lower at an earlier stage in processing, you get a lower synesthete driven by the visual appearance. If it's expressed selectively higher up in the vicinity of the angular gyrus, you get a higher synesthete driven by the numerical concept rather than by the visual appearance.

OK next question - why did this gene survive?

One in two hundred people have this peculiarity of seeing coloured numbers and it's completely useless so why hasn't it vanished from the population and I'm going to suggest it's a bit like sickle cell anaemia - there's a hidden agenda. These genes are doing something else important. What? Well one of the odd facts about synesthesia which been known for a long time and again been ignored, is the fact that synesthesia is much more common among artists, poets, novelists, you know flaky types! So now why is it much more common? Well one view is that - in fact according to one study it's seven times more common among artists poets and novelists and the reason is what do artists, poets and novelists all have in common? Just think about it. What they all have in common is they're very good at metaphor, namely linking seemingly unrelated concepts in their brain, such as if you say "out out brief candle", so it's life, why do you call it a candle? Is it because life is like a long white thing? Obviously not. You don't take the metaphor literally, although schizophrenics do and we won't go into that. So why do you that? Well it's brief like a candle, it can be snuffed out like a candle, it illumines like a candle very briefly. Your brain makes all the right links and Shakespeare of course was a master of doing this. Now imagine one further assumption - if this gene is expressed more diffusely instead of being just expressed in the fusiform or in the angular, if it's expressed in the fusiform you get a lower synesthete, in the angular gyrus TPO junction you get a higher synesthete. If it's expressed everywhere you get greater hyperconnectivity throughout the brain making you more prone to metaphor, links seemingly unrelated things because after all concepts are also represented in brain maps. This may be seem counter-intuitive but after all a number, there's nothing more abstract than a number. You can have five pigs, five donkeys, five chairs - it's fiveness - and that's represented in a fairly small region namely the angular gyrus so it's possible that concepts are also represented in brain maps and these people have excess connections so they can make these associations much more fluidly and effortlessly than all of us less-gifted people.

Now, remember I said the third thing you have to do in science is show that this is not just some quirk. It has vast implications. Well what implications does synesthesia have? I'm going to show all of you that synesthesia is not just a quirk in some people's brain. All of you here are synesthetes, and I'm going to do an experiment. I want all of you to imagine in front of you, to visualise in front of you a bulbous amoeboid shape which looks a bit, has lots of curves on it, undulating curves. And right next to it imagine a jagged, like a piece of shattered glass with jagged shapes. And just for fun, I'm going to tell you this is Martian alphabet. Just as in English alphabet, A is a, B is b, you've got each shape with the particular sound, this is Martian alphabet and one of these shapes is kiki and the other is booba, and I want you to tell me which is which. How many of you think the bulbous shape is the kiki, raise your hands? Well there's one mutation there. In fact what you find is if you do this experiment, 98% of people say the jagged shape, the shattered glass is kiki, and the bulbous amoeboid shape is a booba. Now why is that? You never learnt Martian and nobody here is a Martian. The answer is you're all synesthetes but you're in denial about it. And I'll explain. Look at the kiki and look at the sound kiki. They both share one property, the kiki visual shape has a sharp inflexion and the sound kiki represented in your auditory cortex, in the hearing centres in the brain also has a sharp sudden inflexion of the sound and the brain performs a cross-modal synesthetic abstraction saying the only thing they have in common is the property of jaggedness. Let me extract that property, that's why they're both kiki. So what? Well I'll explain.

We have taken the same patterns I have just told you about, the booba/kiki, and shown them to patients who have damage, very small lesion in the angular gyrus of the left hemisphere and guess what? If you show them these two shapes and ask them to associate kiki with the two shapes, kiki and booba, they're random and by the way we don't use just these two shapes. We have a whole set of them and they cannot do this cross-modal associations even though they're fluent in conversation, they're intelligent, they seem normal in other respects. This makes perfect sense because the angular gyrus is strategically located at the crossroads between the parietal lobe (concerned with touch and propriaception) the temporal lobe (concerned with hearing), occipital lobe> (concerned with vision) so it is strategically placed to allow a convergence of different sense modalities to create abstract modality-free representations of things around you. Now think of what this involves. Think of the jagged shape and the sound, kiki. They have nothing in common. One is photons hitting the retina in parallel, and the other is a sharp sound hitting the hair cells sequentially but the brain abstracts the common denominator saying - but jaggedness is common, or the property of undulation is common, so what you're seeing here in the angular gyrus is the beginnings of a property that we call abstraction that us human beings excel in. And another point I'd like to make is why did this ability evolve in humans in the first place, cross-modal abstraction? Well it turns out if you look at lower mammals, compare them with monkeys, then compare them with the great apes and then with humans, there's a progressive enlargement of the TPO junction and angular gyrus, almost an explosive development and it's especially large in us humans. Why? Well I think this ability evolved because imagine your ancestors scurrying up on the treetops trying to grab branches, jumping from branch to branch, they've got a visual horizontal branch and then they have to adjust the angle of the arm and the fingers so that the proprioceptive map has to match the horizontality of the visual appearance and that's why the angular gyrus became larger and larger. But once you develop this ability to engage in cross-modal abstraction, that structure in turn became an exaptation for other types of abstraction that us humans excel in, be it metaphor or any other type of abstraction, so that's the claim being made here.