View from here: SUSAN GREENFIELD

It would be impossible for anyone not to have reacted with sadness, if not complete shock, at a recent proposal to teach primary school children about the dangers of drugs. It was necessary, we were assured, because there were nowadays many streetwise eight-year-olds who knew much more about all manner of psychoactive substances than their teachers. As a neuropharmacologist, I wonder what exactly these potential mini-junkies are so clued up about, and what exactly they are to be told further.

When it comes to "knowing all about" drugs, presumably a child knows the different names, what the drugs look like, how they are taken, and how much they cost. But I wonder how well they can really talk about the most important issue - the effects. Knowing buzz words for a hyper-aroused state, or tranquillised calm, may not be enough to encompass the full range of feelings from the sensory distortions of LSD to the paranoia of speed, to the depersonalised sensation allegedly resulting from a tablet of ecstasy (tellingly from the Greek to "stand outside of the self"). Such sensations are bewildering and hard enough for a fully fledged adult to describe and evaluate, but an eight-year-old... It strikes me that their "knowledge" after all might need some assistance.

I try to imagine standing in front of a class of eight-year-olds who "know all about drugs". I'm not going to moralise, not because I do not think taking drugs is "wrong", but simply because, in my own experience, merely telling people they should not be doing something is rarely very effective for very long. Instead, I'm going to tell them how drugs actually work on the brain. Perhaps an eight-year-old does not even know really what a brain does, nor even what it looks like. So, the first issue would be to establish that it is the sludgy thing between your ears that makes you the person you are. It doesn't just determine whether or not you are "brainy", but is the amazing system responsible for all your memories, your preferences, the world inside your head that no one else can share first-hand. Unlike the machine-like operations of a heart, likened to a pump, or of lungs, so reminiscent of bellows, the functioning of the brain presents one of the most exciting challenges to science - including understanding how drugs can distort feelings in so many different ways.

Inside the brain, millions of tiny signals are being incessantly shuttled from one part to another. These signals depend on a chemical (transmitter) to be transferred from one of the hundred billion brain cells to the next. There are many different transmitter systems, and different drugs will change each of them in a different way. Why should this chemical modification of chemicals in the brain be so bad? The answer lies in the fact that drugs transform normal chemical signalling in the brain, into a gross caricature, over both space and time.

When transmitter chemicals are normally enabling signals to be passed along, the action is very precise in highly specific brain circuits. Since a drug is not given directly into the brain, it will gain access from the mouth, the nose, the bloodstream, to soak abnormally large banks of brain cells. And over time, there can be further unnatural consequences: imagine shaking hands over and over. Eventually your hand would become numb, and you would need to squeeze the proffered hand to regain some of the initial sensitivity. When transmitters have arrived at their target cell, they usually enter into a molecular handshake to trigger the onward transmission of the signal. However, if the target is bombarded by a drug impostor instead, it too will become eventually less sensitive and need increasingly more drug to have the same initial effect: addiction.

Such heavy-handed chemical tampering with brain connections might have very severe consequences. Current research suggests that every momentary experience has slowly been making your brain circuits configure in a way that is special for you. Thanks to brain connections, your brain is like no one else's, not even if you are a clone, an identical twin. Of course there is the inevitable retort that this scenario is no bad thing. That if drugs make you a different person, so be it. Indeed, many might consider taking drugs for precisely that end, or simply not to change into another personality so much as to be the same as everyone else.

If I were a teacher, this is where I would really attempt to convey how exciting it is to be an individual, and to respect individuality in others. More than any other species we can escape the dictates of our genes, by making the most of experience. Pet goldfish are, frankly, interchangeable for all the character that can be appreciated by the owner, but cats far, far less, and human beings not at all. Our long childhood, tipping the balance away from Nature to Nurture, gives us the chance to develop a unique personality, and it is precisely those carefully nurtured and highly delicate, restless connections between neurons, that drugs can swamp. My message to the eight-year-olds who know all about drugs would therefore extend to a tour of the brain, the advantages of being a child for a long time - and the undesirability of being a goldfish.

The writer is professor of pharmacology at Oxford University.