JUNKIES COULD TEACH US A THING OR TWO ABOUT PURE DESIRE

FORGET fornicating monks and American presidents. For a lesson on lust in
its purest, most pathological form, think drugs. Think cocaine, heroin and
nicotine--and how slavishly addicts crave them.

That, at any rate, is the advice of Anna Rose Childress. And to be fair to
this University of Pennsylvania psychologist, she does--unlike the monks
and presidents--practise what she preaches. For years, Childress has been
studying the intense cravings of cocaine addicts, trying to work out what
these feelings really consist of in the brain. Think of strong sexual
desire and multiply it ten thousandfold, some of her patients have told
her. Now Childress is calling their bluff. She and her colleagues are
trying to find out whether the urge for drugs really is like the urge for
sex--or whether we automatically use sex as the benchmark to describe all
our desires.

Childress isn't the first to suspect that addictive drugs home in on and
corrupt brain systems that evolved to make us succumb to other temptations
of the flesh. There's plenty of evidence from lab rats pointing in this
direction, and when you think about it, it would have been pretty
profligate of natural selection to give our brains separate "desire
systems" for everything from ice cream and claret to the smiles of young
female interns.

Even so, no scientist has previously pursued the common ground between sex
and drugs by sending colleagues out to the local video shop for some sex
films. Nor has anyone previously shown such movies to a bunch of willing
males while scanning their brains. Childress has done both.

The idea grew out of earlier experiments on cocaine craving, when her team
measured the blood flow of addicts watching a home-made video showing
people pretending to buy and use drugs. As the addicts craved, a couple of
structures lit up deep in the brain's limbic system, seat of our basic
emotions. But higher up in the cerebral cortex, home to reasoning and
willpower, there was no more activity during drug craving than there had
been when the addicts were watching a wholesome nature video.

Losing Control

That fits with what many researchers have suspected about drug urges: that
they well up from the brain's evolutionarily ancient inner circuitry.
Childress says craving is "about losing control to the old brain and not
thinking about the consequences".

And if that sounds like an apt description of the average middle-aged man's
capacity to make a fool of himself sexually, you could be right. It's early
days with the sex study, but preliminary findings suggest that those
explicit videos also stimulate the same parts of the limbic brain.

The identities of the two structures that flare up also make perfect sense,
says Childress. One of them is the anterior cingulate, which helps control
the attention levels so crucial both to a drug deal or for focusing on an
object of desire. The second structure is the amygdala--a thoroughfare for
incoming information that plays a part in alerting us to possible dangers
or rewards, as well as enabling the brain to form Pavlovian associations.

Again, this adds up. Over time, addicts report that everything associated
with using drugs comes to seem important. A mere glimpse of a dealer or old
drug haunt is often enough to trigger overwhelming desire. Similarly, sex,
in the form of scantily-clad women--or these days, men--is invariably used
to build powerful associations between, say, cars and desire. As Childress
observes: "They're hoping your amygdala will link these two so that
hereafter cars will take on a rosy glow for you."

Of course, having a brain that is alert to naked bodies or drug cues in the
environment isn't the same as desiring sex or drugs. Besides, urges wax and
wane, and sometimes we cave in and sometimes we don't. To home in on the
seat of desire in the brain, we must take a closer look at craving.

One theory sees craving as an inevitable outgrowth of withdrawal. People
get into a negative state of mind and body because they're not getting the
things they're used to or need. They crave whatever it is that will make
them feel normal--food if they're starving, heroin if they're a junkie,
fornication if they're a sex-starved monk.

A second theory casts craving in a more hedonistic role: once you've
experienced the buzz of that chemical high or orgasm, your brain commands
you to experience it again. In this view, craving is the drive for some
sort of euphoric release. And of course, the more miserable you're feeling,
the more desirable that pleasure seems.

In fact, neither view quite stacks up. Take nicotine withdrawal. In a
pioneering study at the University of Pittsburgh, Saul Shiffman and his
colleagues have found that the cravings which lead so many former smokers
to relapse are not caused by withdrawal symptoms. They are not even caused
by not smoking.

The problem with most research into craving is that it relies on people's
reports of how they felt just before they were faced with temptation. But
memories are fallible. So what Shiffman and his team did was to supply 214
volunteers about to stop smoking with palmtop electronic diaries.

In the days leading up to "quit day", and for weeks afterwards, the
volunteers had to record the date, time, duration and intensity each time
they craved a cigarette, together with information about what they were
doing at the time, and how they were feeling. The palmtop computers were
also programmed to beep randomly and request answers to the same questions
so the researchers could measure background levels of craving too.

Against the odds, the electronic diaries revealed that the cravings for
cigarettes became less intense and less frequent during periods of
abstinence than they were when smoking was "allowed". The lesson here, says
Shiffman, is that the best way of stimulating craving and keeping it at a
high level is to keep taking the drug.

That accounts for the proverbial first drink which triggers the alcoholic
binge, but it also raises another question. If abstinence weakens craving,
why is staying on the wagon so difficult?

One answer might be that craving is not what pushes most addicts over the
edge after all. Shiffman's electronic diaries tell a different story,
however. Volunteers with the strongest urges to smoke turned out to be the
ones most likely to relapse later that day or the next. So craving is a
factor in relapse and we are still left with the puzzle of why abstinence
is such hard work for so many people.

Pleasant Urges

Shiffman says that while drug urges do become weaker and less frequent
after quitting, they also become more tormenting because silencing them
with a quick smoke or fix is no longer an option. The electronic diaries
support that view: before "quit day", the smokers were not only less likely
to rate their urges to smoke as unpleasant, but they sometimes described
them as enjoyable.

So perhaps pleasure-seeking is what craving is really all about? Wrong
again, say Kent Berridge and Terry Robinson of the University of Michigan
in Ann Arbor. Based mainly on rat findings, their papers attack the
everyday assumption that "wanting" and "liking" are two aspects of the same
thing. In most normal situations, they say, yes, desire and pleasure do go
hand in hand. But it's a superficial marriage. In the brain, wanting and
liking are handled by different chemical systems, and while these systems
usually move in concert, it's not hard to push them in opposite directions.

Berridge and Robinson have recently discovered how to do this with food.
Normally, lab rats will not just pursue sugary snacks in a maze, they will
lick their mouths and paws with rodent-like pleasure when consuming them.
That changes, however, when you destroy--or block with drugs--cells just
beneath the limbic system that specialise in producing the neurotransmitter
dopamine. Now the animals will no longer seek out food, yet, say Berridge
and Robinson, they still appear to enjoy the sugary snacks when the
experimenters force them on the rats. What's been snuffed out is not the
liking of food, but the wanting of it.

In addicts and others plagued with compulsive desires, the opposite
happens: the impulses from the brain's "wanting" system are revved up and
cut loose from feelings of pleasure. Desire, as Berridge puts it, "gets a
life of its own".

He does seem to have a point. Over time, addicts grow to want heroin and
cocaine more and more, yet often claim to like them less and less. As for
nicotine cravings, they're clearly out of all proportion to the pleasure
the substance gives (it's actually a poison, remember).

But perhaps the most striking evidence that desire need not be wedded to an
expectation of pleasure comes from research showing that the desire for
drugs can influence people without them being aware of it. Bizarre as it
may sound, wanting can be an entirely unconscious process, neither
propelled nor accompanied by feelings of any kind.

In lab studies, for example, human heroin addicts will, like rats, press a
lever to obtain pleasurable injections of morphine. No surprises there.
Less predictably, though, the same addicts will, later on, also work hard
at pressing a lever for tiny doses that produce no buzz at all--despite the
fact that sham injections fail to move them to press a lever. When
questioned, the drug users cannot explain why they are prepared to work for
the boring real injections but not for the equally boring sham injections.

So what is motivating them? Desire. Not the rich and complex kind that a
Nabokov or Lawrence would write about, but a stripped down, primitive
version. Those tiny morphine doses are whetting the addicts' appetites, but
imperceptibly. They are pressing a "want" button deep in the brain's
unconscious inner circuitry.

At last, then, we seem to be closing in on the place where the seeds of
desire are actually sown. Berridge and Robinson suggest we look no further
than the network of nerves in the brain that includes the
dopamine-producing cells they fiddled with in rats.

Sometimes known as the "reward pathway", the network runs through the heart
of the limbic system, receiving signals from the brain stem. It is famous
among addiction researchers because drugs such as cocaine, heroin and
nicotine all stimulate it to pump out dopamine. Until now, it's been
unclear whether the pathway is mainly a font of pleasure or of desire, but
Berridge and Robinson argue there are good reasons for regarding it as a
desire system.

They point out that in rats the pathway starts pumping out dopamine before
they get the sugary snack, shot of heroin or copulation they so enjoy. Also
addictive drugs don't just stimulate this nerve network in the short-term,
they crank up its long-lasting sensitivity. Robinson says that the pathway
becomes hyperactive, just as you'd expect if it had more to do with
long-lasting drug effects like vulnerability to craving than with
short-term pleasures.

So much for lab observations. What about the real world? Here, predictably,
not everyone believes the distinction between wanting and liking is quite
so clear-cut. Childress says that human drug users tend to get more empathy
if they insist they no longer enjoy it, much as a philanderer insists the
sex was not enjoyable. "My patients," she says, "both want and like, and
both are intense."

Either way, if fornicating monks of bygone centuries had known about this
slither of nerve tissue, they would probably have seen it as the devil's
own work: the physical seat of temptation. Not that it would have done them
much good. For as Aldous Huxley reminds us: "A firm conviction of the
material reality of Hell never prevented medieval Christians from doing
what their ambition, lust or covetousness suggested."*

And like every drug user, Huxley knew a thing or two about temptation.

* Aldous Huxley, The Doors of Perception, 1951