When was the last time you saw Bono head-butt The Edge? Maybe Bono head-butted him after he went and lost their record at a photo shoot in France a few months ago? Maybe not? (I would have). U2 just aren't a head-butting sort of band.

The lead vocalist head-butting the guitarist: alongside fistfights, the use of instruments as weapons (the bass guitar is particularly good, you'll find) and more generic types of physical violence are an integral part of rock 'n' roll's rich history. And we're not talking about the sort of girly handbag stuff that Noel and Liam get up to. (Sample: "You're a wanker." "No, you're a wanker"). We're talking the actual sound of fist on skull, or whatever is appropriate and to hand at the time.

Now, though, The Man has stepped in to ruin it all. Scared that their big-selling bands are in danger of imploding due to mutual loathing, record companies are hiring what are euphemistically known as performance coaches (PCs) to get bands "to talk through their anger" and all that sort of stuff.

You 'll see these coaches in the upcoming Metallica documentary Some Kind of Monster, in which the band's PC got the members (who all famously hate each others' guts - why else do you think their music sounds as it does?) to "excavate deep-rooted resentments".

It's funny, but it's always the scary metallers who go running for the intensive group therapy when the head-butting breaks out. Others who have fessed up to group therapy are Slipknot (rows about masks, no doubt) and Audioslave, who have been chanting happily about "breaking down defences" ever since their session.

Even higher-profile bands have sought out the healing hands of these grossly overpaid PCs (Metallica coach Phil Towle was on $40,000 a month). But apparently there's something about doctor- patient confidentiality which has to be respected.

Bands who have been forced by their label to call in a PC report that the trauma that gets dredged up varies from "you stole my groupie" up to "you stole my wife". Before they even begin to address these issues, though, the overriding problem of substance abuse has to be tackled - which is why it took Aerosmith so long to be hauled back in from the brink.

"PCs are brought in by the label because no one wants to spoil the party," says Dr Lou Cox, author of the upcoming Why Successful Bands Fail. "This happens when the honeymoon period is ending and the high of success is waning, so that the tension produced by the band's dysfunction reaches the boiling point and forces the band into a confrontation with its own internal self-destructive forces."

A classic cause of inter-band tension is touring. Even slightly less dysfunctional bands are now being dragged in for sessions on how to cope with life on the road. "Issues" are cleared up at an early stage and "defences" broken down to turn the whole experience into a travelling happy-clappy holiday. But speak to any band towards the end of a 68-date tour, and you tend to find that the petty resentments are very much live and kicking all over again.

A key part of any PC's bag of tricks is that he/she will typically (and this is sadly true) have to "decriminalise the fact that they all have egos". I think that particular notion needs a bit more workshopping, all things considered.

Increasingly what is being seen now is that these PCs are being brought in as a preventative measure, with reports of some managers seeking professional help for their charges just after they have been signed.

This is all fantastic in a "let's break through our communication block" type of way. But you will find, even after a cursory look at it, that some of the best music ever created has been by people who were deeply and irrevocably dysfunctional even before the word was invented. Let's workshop that idea.