Put it down to a blinding flash of genius

Headache World 2000 sounds like a peculiarly hellish kind of theme park. In fact it's one of those plenary gatherings of specialists that come with their own badged briefcase and limitless opportunities for collegiate networking. The event's website ringingly declares that it will "go where no international headache meeting has gone before".

Headache World 2000 sounds like a peculiarly hellish kind of theme park. In fact it's one of those plenary gatherings of specialists that come with their own badged briefcase and limitless opportunities for collegiate networking. The event's website ringingly declares that it will "go where no international headache meeting has gone before".

The event has already attracted a bit more publicity than the average clinical shindig thanks to a forthcoming lecture by a Dutch doctor, Michel Ferrari, who believes that Picasso's fractured portraits may have been inspired by the classic visual disruptions of a migraine headache. The fact that Picasso never complained about migraines does not rule out this theory, since it is not unknown for people to experience the migraine aura without the pain.

Naturally, this story is a profoundly attractive one for journalists, because it allows them to substitute an easily explicable disability ("tormented vision of a migraine sufferer") for a mysterious ability ("creative genius").

It is hardly the first time that someone has ventured a diagnostic approach to great works of art, treating them as expressions of disease rather than imagination. The classic text for aesthetic pathologists is The World Through Blunted Sight, by the eye surgeon Patrick Trevor-Roper - a study of the stylistic implications of various artists' sight problems. Indeed it isn't even the first time that a migraine has been fingered as the muse; Trevor-Roper points out in his book that St Hildegard of Bingen had previously been identified as a sufferer, since she describes her visions as having been preceded by waving lights and flames ("scintillating scotomas" if you want the technical term).

At first glimpse The World Through Blunted Sight has a distinct smack of comedy to it - it calls to mind the country magazine that reviewed Lady Chatterley's Lover as an account of pheasant husbandry interrupted by tedious bouts of love-making - but in fact it's commendably cautious about the limits to such clinical speculations, and full of intriguing details. It notes that both Monet and Cézanne were myopic and both scornful of artificial aids ("Bon Dieu, je vois comme Bouguereau!" Monet said once, rejecting the offer of spectacles. To see indistinctly was bearable, but to see with the clarity of a despised pompier like Bouguereau would have been intolerable.) But it carefully steers away from the obvious tabloid reduction - that Impressionism is simply a way of turning a defect into an advantage: "'It's all a blur to me', says Frog genius, 'and that's the way I like it'."

Patrick Trevor-Roper also provides readers with a clue as to why such stories are so appealing to the common culture, noting in his introduction that the influence of physical and physiological factors on artistic style "could rarely apply outside naturalistic paintings". The point is a straightforward one - it is only in paintings of recognisable objects that we can easily compare a notion of the original with the painter's rendition of it. So, looking at El Greco's portraits, we can measure his distinctive elongation of the figures against our common experience of what human bodies look like. And we can easily be tempted to explain away the discrepancy between the two with an explanation that lies in the realm of medicine rather than that of art.

The problem is that such explanations confuse two distinct kinds of vision - retinal and conceptual. It's a confusion even artists are prone to - Giacometti once protested at critics' attempts to discern metaphysical or poetic meanings in his work, insisting that no such considerations troubled him: "It is a purely optical exercise. I try to represent a head as I see it", he explained. But if it was purely optical, then what on earth did a Giacometti sculpture look like to Giacometti? The truth was that he saw something the rest of us didn't - and that fact is at some level unsettling and in need of a cultural analgesic.

What connects all such enterprises is an attempt to get the artist back on side, back on the naturalistic team. The notion that Picasso might literally have seen something like that jagged face, a confusion of human shards in lurid colours, rehabilitates him as faithful, even scientific, recorder of the perceived world, rather than someone prepared to interfere with it. In other words the migraine theory works as a kind of plea in mitigation for the offence caused by his failure to render the world as we see it plainly every day. To be fair to Dr Ferrari, he's not as simplistic as this, but the general appeal of the story - the instinct that will make people pass it on as a diverting curiosity - lies in that deeply soothing fact.

Well, I say soothing, but frankly it gives me a headache.