Hooked: Why your brain is primed for addiction
26 August 2007, Helen Phillips
David had been a normal, happy child, growing up in an English seaside town. But by the time he was 18 he was miserable,
withdrawn and rebellious. He skipped school, got angry when confronted, and stole from family and friends. He had a habit to
fuel, and it took up all of his time. He lost sleep, had anxiety attacks, and sometimes got violent when he couldn't get what he
David, his parents, and psychologist Mark Griffiths of Nottingham Trent University in the UK, who gathered his case history,
have no doubt that David was an addict. It changed his personality and behaviour, gave him a high, and dominated his
thoughts for four years. The word addict usually triggers images of drug abusers or alcoholics, yet David's "addiction" was not
to any chemical. It was to slot machines, the most innocuous-looking of gambling games, freely accessible to school kids and
open all hours, all year round.
Was David's problem as serious as that of a heroin addict? Is it sensible to lump such behaviour together with addiction to
drugs? Granted, the term addiction is bandied about a little too readily by chocaholics, workaholics and teens who spend a bit
too long playing the latest computer game. "We can't define it simply by excess," says Griffiths. Yet two decades of research
have convinced him that excessive behaviour can cross the line and become every bit as real an addiction as being physically
dependent on a drug.
He's not alone. Several studies of the brain and behaviour back the idea that there's very little biological difference between
what goes on in the head of a gambling addict and that of a crack addict. A growing number of researchers believe that the
same processes lie behind all addictions, behavioural or chemical, whether it's gambling or shopping, computer gaming, love,
work, exercise, pornography, eating or sex. "They have more in common than different," says Sabine Grüsser-Sinopoli, who
runs a clinic and research lab for behavioural addictions at the Charité Medical University in Berlin, Germany. "Addiction is all
That's a controversial claim. There's a common perception that overindulgence in certain behaviours is all down to individual
choice. If you are overeating, oversexed, gambling away your earnings or spending all your time online, you are more likely to
be considered morally abhorrent than the victim of a disease. Calling these problems "addictions" has triggered debates about
whether our society or our biology is to blame, and whether people that fall foul of a behavioural obsession should be offered
help and treatment rather than punishment.
Ironically, research on behavioural addictions is having consequences for addiction more generally. It has spurred researchers
to redefine their models and definitions of addiction, helping them pin down what addiction really means. And it has begun to
reveal how the timing and type of exposure to certain experiences early in life might affect the likelihood of developing an
addiction, suggesting new ideas about how to prevent them.
Whether you consider them true addictions or not, finding ways to attack these problem behaviours is becoming ever more
urgent. More and more people are going to clinics asking for help to control the need to shop, have sex or gamble, because
their behaviour is ruining their lives, says Grüsser-Sinopoli. Technological advances, especially the rise in popularity of the
internet, are increasing the opportunities we have to engage in potentially addictive behaviours. The Center for Online
Addiction, an educational and treatment group founded just over a decade ago by psychologist and internet addiction
specialist Kimberly Young, now of St Bonaventure University in New York, estimates that as much as 5 to 10 per cent of the
US population is addicted to some kind of internet-based activity, be it gaming, gambling, or using chatrooms and email.
Problem gambling is perhaps the most harmful of these. A 2000 survey commissioned by the British National Centre for Social
Research revealed that about 1 per cent of the UK adult population had a pathological gambling problem, and the repeat
survey, due out in a few months, is widely expected to show a rise - especially among women. Some researchers predict as
many as 10 per cent of the US population will soon have a gambling problem. Record numbers of people are signing up to
online gambling sites - the industry is now worth an estimated $12 billion - prompting a new US bill that aims to tighten
restrictions on the practice. Around half of the new entries in this year's "rich list" published by The Sunday Times in London
have made their money running internet gambling sites or casinos.
The debate about whether behaviour can be considered a true addiction is not an entirely new one. In 1975, psychologist
Stanton Peele wrote a book called Love and Addiction, which argued that all kinds of drug and non-drug experiences,
including love, could be described as addictions. At the time, this was a term only really used to describe heroin abuse, he
says. But look at how we talk about a lost love, and how similar to drug withdrawal it sounds: we are unable to think of
anything else or to get out of bed, we're crying and physically in pain. "There really is no way to differentiate the behaviour of
gambling, a love affair or pursuing a drug," he says.
While we all think we know what is meant by the term addiction, surprisingly there is still no scientific consensus about how to
define substance addictions, let alone behavioural ones. Some medical definitions consider addiction a disease, while others
consider it hijacking the normal "reward" signals in the brain (see Diagram). Some textbook definitions include the ingestion of
a substance as an essential part of the definition, which would rule out behavioural addictions entirely. Even now, the current
edition of the Diagnostic and Statistical Manual of Mental Disorders, or DSM-IV, the official manual of psychiatric illness, talks
of dependence and abuse rather than addiction even with drugs, and it lists pathological gambling among conditions such as
Tourette's, as an impulse control disorder.
There are, however, plenty of researchers who now support a broader definition of addiction that includes behavioural
addictions. Griffiths is leading the charge for including extreme obsessive behaviours as addictions. He has been studying
pathological gamblers and people with other behavioural problems for 20 years, and the work has led him to a new definition
for addiction. He says there are a set of key features common to crack, heroin, alcohol and nicotine addiction that describe all
addictions and equally apply to many excessive behaviours. One of those features is that addiction dominates people's lives,
he says, leading to cravings and a complete preoccupation with a habit. This can apply to a behaviour other than substance
abuse. "If a person is addicted, first they have to conduct this behaviour, ahead of all other behaviours: ahead of eating,
drinking or sleeping," says Grüsser-Sinopoli. "They are not doing it because they like it, they are doing it because they have
to." Take David, whose slot machine obsession destroyed his life for a number of years. Another of Griffiths's case studies,
Joanne, was addicted to exercise and even admitted to walking out of her university exams to satisfy her craving (see "The
Another feature in Griffiths's broader definition is tolerance - a well-established feature of drug habits - meaning that as time
goes on, a greater dose is needed for the same high. It's a feature that's starting to be documented in behaviours too, says
Griffiths. He measured the heart rate of gamblers, for example, finding that slot machine players all experience a quickening of
the pulse as they play - the sign of a rush, rather like a drugs high. In new or less experienced players, the rate remains high
for the duration of play, but in regular gamblers, the rise is only transient. To maintain the effect, they have to gamble faster,
longer and take greater risks.
One of the most disturbing and defining features of addiction is withdrawal. Griffiths says that addicted gamblers who are
unable to engage in their habit feel similar symptoms, such as excessive moodiness, irritability, nausea, stomach cramps,
headaches and sweats. "These are real effects," he says. "Gamblers have withdrawal symptoms like drug addicts." Grüsser-
Sinopoli has seen patients with anxiety, depression, and physical symptoms such as sweating and hallucinations, triggered by
withdrawal from shopping and gambling.
The evidence that behavioural addictions are very similar to chemical ones is mounting from brain studies too. According to
addiction specialist Eric Nestler of the University of Texas Southwestern Medical Center in Dallas, drug addictions and
"natural" addictions seem to involve shared pathways in the brain. "Take a person with sex addiction, or a pathological
gambler: their brains all show abnormal responses - the same reactions to drugs of abuse," he says.
All pleasurable stimuli, natural and unnatural, act on the same "reward" circuitry in the brain. When we find something
desirable, the brain chemical dopamine is released in the brain. Drugs of abuse all cause dopamine release, triggering a
desire to keep taking them. Pleasurable behaviours are rewarding too and also release dopamine. The fact that behaviours
and drugs of abuse converge on the same brain circuit is not enough to prove they can both be addictive, but there are more
specific changes that do seem to be characteristic of addiction.
For example, new research has shown that higher than normal dopamine levels are associated with some behavioural
compulsions (see "Addiction by stealth"). There are also signs that, just as recovering drug addicts may have abnormally
strong memories of drug paraphernalia and drug-taking locations that can trigger irresistible cravings, so obsessive computer
gamers may have abnormal memories too.
Grüsser-Sinopoli and her colleague Ralf Thalemann found that gamers or gamblers experienced cravings, triggered by images
from their favourite games, that were comparable to the responses of drug addicts. They had heightened physiological and
EEG brain responses to the images, indicating that they were more pleasing and motivationally relevant than they were to
inexperienced players. An addict's brain learns to respond much more dramatically to previously innocuous scenes, says
They have conducted the same tests in cannabis, heroin and alcohol addicts, casino employees, abstinent gamblers and
people undergoing methadone and naltrexone treatment. They found that this EEG response shows up in all addicts, but not
in people who are exposed to the same surroundings yet remain unaddicted, such as casino employees. "People may deny
they have a craving, but when we expose them to these cues the system is still active," she says.
Nestler and his colleagues have recently discovered another physical marker of addiction. In chronic drug users there seems
to be a distinctive rise in production of a gene regulator called delta Fos B in a part of the reward circuit called the nucleus
accumbens. It shows up in the brains of rodents that compulsively consume drugs or alcohol, and although it is hard to test
behavioural addictions such as gambling in a mouse, it has also shown up in animals that are allowed to have sex more often
than a control group.
One other compulsive behaviour that has been controversial in the discussion of addiction is eating behaviour. Whether we
could actually get hooked on food is controversial, but there are signs that delta Fos B rises in animals that compulsively
consume sugar, suggesting sugar might be addictive in some cases.
Bart Hoebel, a psychologist from Princeton University, believes we can be addicted to food - at least to sugar (New Scientist, 1
February 2003, p 26). He has shown that rats bingeing on sugar release dopamine in the same way as rats given high doses
of addictive drugs, and doing so can cause lasting changes in the dopamine system, withdrawal symptoms and cross-
sensitisation to other drugs, including amphetamines. Very sweet foods can induce a form of dependency, he believes.
One thing that this focus on behavioural addictions highlights is that we all have the potential to be addicts, says Jim Orford of
the University of Birmingham, UK, author of a report on behavioural addictions for the UK Office of Science and Technology.
"Almost any of us can become behavioural addicts, given the right exposure, the right timing and so on," he says. "But there
are multiple causes: our personalities, genetics - it's not simple." Why some people develop addictions while others can safely
dip into these activities with no ill effects is still unknown.
One thing Orford is certain of is that these behavioural addictions will only increase over the next few years. Not everyone will
try an illegal drug or hit a casino, but most of us use computers, and many more people are playing computer games or
gambling online than ever before. We need to be ready to treat people with these new addictions.
The key here will be addressing underlying emotional problems, says Grüsser-Sinopoli. She has conducted surveys in schools
that show children are more likely to turn to computer games when they are unhappy. Since we can't keep people away from
computers or shops for the rest of their lives, learning how to cope with stress will be key to stemming the huge rise in
behavioural addictions, Grüsser-Sinopoli says.
She also believes that for the worst cases, drug treatments such as naloxone and naltrexone, used to help people with alcohol
and heroin addictions, may help, because the underlying addiction mechanisms are so similar. To really prevent a large rise in
behavioural addiction, we will need to accept that the solution will be removing the easy access to stimuli that we just can't
"Gambling can be as serious as a drug addiction, yet it is a government-subsidised form of addiction," says Nestler. "We need
to be made more aware of the potential risks, and we need as a society to worry about what we do, and remove subsidies for
addictive behaviours, tobacco, gambling, state lotteries - it's absurd."
So far, the advice has fallen on deaf ears. Although both the US and UK have recently changed their gambling laws,
attempting to regulate and restrict some activities, the laws will not restrict slot machines. They will remain readily available to
adolescents, the most vulnerable age group for any addiction. "Slot machines are an unbelievable anomaly in law," says
Griffiths. "They are one of the most addictive forms of gambling available."
Australia has already discovered how damaging it is to make games machines readily accessible and attractive. Poker
machines, or "pokies", offering million-dollar jackpots have become freely available in bars and clubs all over the country over
the past two decades as the government has relaxed its gambling laws. It has taken problem gamblers losing thousands of
dollars a year, estimates of the number of Australian adults who gamble to top 80 per cent, and maybe 2.3 per cent of the
adult population being problem gamblers for the political will to start changing.
Whether behavioural addictions, such as playing slot machines, are a gateway to more physically harmful ones is still hotly
debated, just as it is with drugs. There are signs that teenage exposure to gambling or gaming seems to predispose the
developing brain to more severe problems later, says Griffiths.
Peter Whybrow, author of American Mania and director of the Semel Institute for Neuroscience and Human Behavior at the
University of California, Los Angeles, agrees that our changing environment has led to the huge prevalence in behavioural
addictions. "We have created a fabulous new environment with lots of wonderful opportunities, but completely different from
the scarcity in which our reward systems evolved," he says. Under conditions of extreme affluence we are putting these
systems into overload, he believes. The only thing that stops us is self constraint. "If politicians and leaders understood how
the brain works, they would not be building society as they are doing."
The exercise addict
Joanne, 25, doesn't see herself as an addict, though her habit takes up several hours of each day, occupies her thoughts
continuously, and has even made her walk out of university exams. She is obsessed with exercise, mostly a type of martial
arts, but any form of exercise will do. She describes the buzz as like being on amphetamines. She has developed a tolerance
for it, and so has to exercise ever longer for the same effect, working out for several hours a day now just to feel normal. If she
can't, she gets anxious and irritable, and suffers headaches and nausea. She spends beyond her means to fund her habit, and
has lost friends and her partner to it.
Addiction by stealth
Max Wells, a retired physician from Austin, Texas, is testing his own theory of gambling addiction in the US courts. He claims,
in a lawsuit filed this February, that his Parkinson's medication was to blame for a gambling addiction that lost him $14 million.
This is not the first time Parkinson's disease and prescription medications for it have been linked to compulsive behaviour,
though it's possibly the most high-profile. Wells cites the findings of a study by Leann Dodd from the Mayo Clinic in Rochester,
Minnesota, published last year, which described 11 people with Parkinson's who developed gambling and other behavioural
problems including sex and eating addictions, seemingly as a direct result of taking dopamine replacement medication. The
most common of these in Dodd's clinic was pramipexole, a similar drug to that taken by Wells. Dodd has since described
several more cases.
Wells's claim against GlaxoSmithKline and seven Las Vegas casinos hinges on whether there were adequate warnings about
possible side effects of the drug Requip (ropinirole), and also on the claim that the casinos knew about his condition, should
have known about the risks associated with his medication, yet let him continue to gamble.
More therapy, please
Andrew Lawrence, a neurologist from the University of Cambridge, has also been looking for Parkinson's patients afflicted by
addictions. He says it is rare - he has traced just 20 or so affected people in the UK over five years. But he has found that
those patients who become addicted to the dopamine replacement therapy itself, abusing it and taking far more than
recommended, and even stealing or deceiving doctors to get hold of the supplies, are the ones who also suffer behavioural
Lawrence is trying to understand what the finding tells us about the process of addiction. "There is some strong link underlying
vulnerability to drug addiction that increases vulnerability to compulsive behaviour," he says. "Exposure to drugs of abuse
could potentiate natural reward centres and spill over from drug motivation to sex or eating behaviour."
What is clear is that unnaturally high levels of dopamine seem to be related to behavioural compulsions - some of the best
evidence yet that there's a real biological cause of behavioural obsessions that looks very much like drug addiction.
What has never been clear with addiction is what predisposes some people more than others. Some researchers think that
addicts may start with underactive brain reward systems, and that their habits stem from self-medication. Others think the
opposite, that they start with overactive dopamine circuitry and thus the motivation or incentive to partake is greater and harder
to resist than normal.
Lawrence's brain-imaging studies in people with Parkinson's suggest that the latter is most likely - they have increased
motivation. He found that people who suffered cravings on Parkinson's medication had higher than normal levels of dopamine
in their reward circuits and that the amount correlated with how much drug craving they experienced. He is now looking at
It's a timely debate, he says, as gambling laws are changing and accessibility is increasing. "There will be a problem for
vulnerable individuals," he says.
The computer addict
Jamie is a 16-year-old only child, living alone with his mother. He spends around 70 hours a week on his computer. He admits
that the internet is the most important thing in his life - he likes socialising online with fellow science-fiction buffs, though he
has few friends in the real world. He is overweight and unconfident, but he says the internet improves his mood. He thinks
about it all the time, and gets withdrawal symptoms, becoming irritable and shaky if he cannot go online when he wants to. He
sleeps irregularly, mostly logging on at night, but he denies he is addicted to his computer.
The unsuspecting gambling and sex addict
Graham, a 41-year-old computer programmer, had never gambled in his life until he was put on a new medication for
Parkinson's disease that boosted his dwindling dopamine levels. Within a month of commencing the treatment he was
consumed by the desire to gamble on the internet, losing $5000 within a few months. He also bought many items he didn't
need, and was fixated on sex with his wife. When his neurologist reduced the medication, the habits were switched off "like
turning off a light".
25% of members of Gamblers Anonymous UK have a problem with fruit machines
$11.9 billion - global internet gambling revenue in 2005
2000 estimated number of internet gambling sites
23 million - number of online gamblers in 2005, 8 million of whom are in the US, 4 million in UK
75% of adults in the US have gambled in the past year
$82.2 billion - global gambling revenue in 2005, estimated to rise by over 50% by 2010
60 million - obese adults in the US
83% of 8 to 18-year-olds have a video game player
2 hours - time spent gaming each day in average US household
31 hours - average time spent online per month worldwide
9 kilograms - amount of chocolate consumed per person per year in UK
From issue 2566 of New Scientist magazine, 26 August 2006, page 30-35