www.sciencemag.orgN E W S F O C U
S
'Behavioral' Addictions: Do They
Exist?
Getting a fix.
Gamblers
get high and show tolerance and withdrawal symptoms - a lot like
drug
addicts. Aided by brain imaging advances, scientists are looking for
evidence that compulsive nondrug behaviors lead to long-term changes in
reward circuitry
The concept of addiction is changing, as this
special news package
describes: There 's more emphasis on how drugs and even
behaviors may wreak
long-term damage to the
brain.
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People
toss around the term "addiction" to describe someone's relationship
to a
job, a boyfriend, or a computer. But scientists have traditionally
confined
their use of the term to substances - namely alcohol and other
drugs - that
clearly foster physical dependence in the user.
That's changing, however.
New knowledge about the brain's reward system,
much gained by super-refined
brain scan technology, suggests that as far as
the brain is concerned, a
reward's a reward, regardless of whether it comes
from a chemical or an
experience. And where there's a reward, there's the
risk of the vulnerable
brain get-ting trapped in a compulsion.
"Over the past 6 months, more and
more people have been thinking that,
contrary to earlier views, there is
commonality between substance
addictions and other compulsions," says Alan
Leshner, head of the National
Institute on Drug Abuse (NIDA) and incoming
executive officer of the
American Association for the Advancement of
Science, pub-lisher of Science.
Just where to draw the line is not yet
clear. The unsettled state of
defini-tions is reflected in psychiatry's
bible, the Diagnostic and
Statistical Manual IV. Addictions, obsessions, and
compulsions - all
related to loss of voluntary control and getting trapped
in repetitious,
self-defeating behavior - are scattered around under
"substance-related
disorders," "eating disorders," "sexual and gender
identity disorders,"
"anxiety disorders," and "impulse-control disorders not
elsewhere
classified." In that last grab-bag are compulsive gambling,
kleptomania,
fire-setting, hair-pulling, and "intermittent explosive
disorder."
Addiction used to be defined as dependence on a drug as
evidenced by
craving, increased tolerance, and withdrawal. But even some
seemingly
classical addictions don't follow that pattern. Cocaine, for
example, is
highly addictive but causes little withdrawal. And a person who
gets hooked
on morphine while in the hospital may stop taking the drug
without
developing an obsession with it.
Now many researchers are
moving toward a definition of addiction based more
on behavior, and they are
starting to look at whether brain activity and
biochemistry are affected the
same way in "behavioral" addictions as they
are by substance abuse. One who
endorses this perspective is psychologist
Howard Shaffer, who heads the
Division on Addictions at Harvard. "I had
great difficulty with my own
colleagues when I suggested that a lot of
addiction is the result of
experience . repetitive, high-emotion,
high-frequency experience," he says.
But it's become clear that
neuroadaptation-that is, changes in neu-ral
circuitry that help perpetuate
the behavior - occurs even in the absence of
drug-taking, he says.
The experts are fond of saying that addiction
occurs when a habit "hijacks"
brain circuits that evolved to reward
survival-enhancing behavior such as
eating and sex. "It stands to reason if
you can derange these circuits with
pharmacology, you can do it with natural
rewards too," observes Stanford
University psycholo-gist Brian Knutson.
Thus, drugs are no longer at the
heart of the matter. "What is coming up
fast as being the central core
issue . is continued en-gagement in
self-destructive behavior despite
adverse consequences," says Steven Grant
of NIDA.
Not everybody is on board with this open-ended definition. For
one thing,
says longtime addiction researcher Roy Wise of NIDA, drugs are
far more
powerful than any "natural" pleasure when it comes to the amounts
of
dopamine released. Nonetheless, be-havioral resemblances to addiction are
getting increasing notice.
GamblingIn a
class of its own as the disorder that most resembles drug addiction is
pathological gambling. Compulsive gamblers live from fix to fix, throwing
away the rest of their lives for another roll of the dice-and deluding
themselves that luck will soon smile on them. Their subjective cravings can
be as intense as those of drug abusers; they show tolerance through their
need to increase betting; and they experience highs rivaling that of a drug
high. Up to half of pathological gamblers "show withdrawal symptoms looking
like a mild form of drug withdrawal," says Shaffer- including churning
guts, sleep disturbance, sweating, irritability, and craving. And like drug
addicts, they are at risk of sudden relapse even after many years of
abstinence.
Furthermore, what's going on inside gamblers' heads looks
like what goes on
in addicts' heads. Yale psychiatrist Marc Potenza finds
that when
pathological gamblers are exposed to videos of people gambling and
talking
about gambling, they show activity changes in some of the same
frontal and
limbic brain regions as do cocaine addicts exposed to images
that stir up
drug craving, as assessed by functional magnetic resonance
imaging (fMRI).
And a positron emission tomography study of pathological
gamblers playing
blackjack, conducted by psychiatrist Eric Hollander of
Mount Sinai School
of Medicine in New York City, showed significant changes
in cortical
arousal depending on whether they were just playing cards or
betting with a
$100 stake. He says it resembles another study showing
alcoholics' brain
reactions to looking at a bottle of Coke versus a bot-tle
of whiskey.
Like addicts, gamblers also respond to drugs that block drug
highs. Suck
Won Kim, a psychiatrist at the University of Minnesota Medical
School in
Minneapolis, has tried naltrexone, an opiate antagonist, on a
variety of
compulsive behaviors including gam-bling. In an 11-week trial on
45
gamblers, naltrexone inhibited both the urge to gamble and the high from
it
in 75% of the group- compared with 24% of a comparable group on
placebo-suggesting that drugs and gambling stimulate some of the same
bio-chemical pathways.
And finally, there's cognitive evidence:
Gamblers, like drug addicts, do
badly at a "gambling task," success at which
requires the ability to
perceive that delayed gains will be larger than
immediate ones.
Food
Can food be said to be an
addiction? Overeaters Anonymous-which, like
Gam-blers Anonymous, is
patterned on Alco-holics Anonymous-says yes. The
experts, however, say it
depends on the disorder.
Compulsive overeating certainly has the look of
an addiction that can
dominate a person's life. There's also biochemical
evi-dence suggesting a
kinship. Psychiatrist Nora Volkow of Brookhaven
National Lab-oratory in
Upton, New York, and col-leagues found that in a
group of compul-sive
overeaters, dopamine receptor avail-ability was lower,
an anomaly also seen
in drug addicts. "Dopamine deficiency in obese
individuals may perpetuate
patholog-ical eating as a means to compensate for
decreased activation of
these circuits," Volkow's team
suggests.
Bulimia, which is characterized by bingeing and vomiting, also
looks a lot
like an addiction, Hollander notes. Unlike anorexia, which
involves rigidly
controlled behavior and no high, "bulimia and binge eating
have an
impulsive component-pleasure and arousal followed by guilt and
remorse."
Patricia Faris, a gastrointestinal physiologist at the
University of
Minnesota, Minneapolis, believes that as with drug addictions,
bulimic
behavior is initially voluntary but is transformed into a compulsion
because of changes that it wreaks on the nervous system. Bulimia clearly
affects reward centers: Faris says patients become increasingly depressed
and anxious before episodes; immediately following, they uni-formly report
a pleasant "afterglow."
Faris has come up with a novel hypothesis:
that bulimia disregulates the
vagal nerve, which regulates heart and lungs
as well as the vomiting
impulse. She suspects that a binge-purge episode
then brings the vagal
nerve back to its normal role. This retraining of the
vagal nerve also has
long-term effects on the brain's reward circuitry, she
believes, as
suggested by the fact that bulimics have a high relapse rate
and are very
hard to help once they've been at it for a few years. Kim says
that
although the theory is speculative, he believes Faris is on the right
track
in ap-proaching the problem "from neural system concepts" as opposed
to a
more traditional emphasis on
biochemistry.
SexThere's not much research on
sex as an addiction, and some researchers are
dubious about whether such a
basic function can have that distinction. Sex
is really a distinct subject
because it's "wired separately," in the
opinion of Kim of Minnesota. He
notes, for example, that the opioid
antagonist naltrexone "really doesn't
affect sexual desire that much," so
it doesn't follow the same pathways as,
say, gambling.
Yet so-called sex addicts do display be-haviors
characteristic of
addiction: They obsess about whatever their favorite
practice is, never get
enough, feel out of control, and experience serious
disruption of their
lives because of it. That leads Shaffer to conclude that
some behaviors
qualify as sex addictions: "I think those things that are
robust and
reliable shifters of sub-jective experience all hold the
potential for
addiction."
To be sure, he adds, sex trails behind
drugs or gam-bling, being
"relatively robust but unreliable" in delivering
satisfaction.
Anna Rose Childress, who does brain imaging studies at the
University of
Pennsylvania in Philadelphia, says sex addicts resemble
cocaine addicts and
probably share with them a defect in "inhibitory
circuitry."
In both instances, "people say when they're in this big 'go'
state they
feel as though there is override [of inhibition] . a feeling of
being
unable to stop," says Childress.
Scientists are just beginning
to use imaging to try to determine whether
there's a tangible basis to these
feelings. Childress has been comparing
the circuits activated by cocaine in
addicts and sexual desire in normal
subjects in hope of identifying the
"stop!" circuitry. And psychiatrist
Peter Martin at Vanderbilt University in
Nashville, Tennessee, says a
pre-liminary study with normal subjects
indicates that brain activity
associated with sexual arousal looks like that
accompanying drug
consumption. He plans to do further comparisons using
self-described sex
addicts.
Shopping,running,clicking .
Although
there is no shortage of therapies for every imaginable addiction,
there is
little or no published research on other disorders. One problem
that
afflicts a great many women, in particular, is compulsive shopping,
says
Kim. Compulsive shoppers typically end up with huge debts and their
houses
stuffed with un-used merchandise. Shopping binges are very often
precipitated by feelings of depression and anxiety, Shaffer says; the
shopping itself can generate temporary druglike highs before the
shopper-like a cocaine addict-crashes into depression, guilt, anxiety, and
fatigue. Some have no doubt this is an addic-tion. "In my clinical
experience, [compulsive shoppers] have a similar kind of withdrawal," says
Shaffer. Kim agrees: "These people can't control it. We think it's
essentially the same thing as gambling." Kim thinks compulsive shoplifting
(kleptoma-nia) is also closely related and, in fact, has published the
first formal study trying doses of naltrexone with kleptomania; 9 of 10
patients, he says, were much improved after 11 weeks of
treatment.
Then there's Internet abuse, the country's fastest growing
"addiction." But
whether any such phenomenon exists is something about which
scientists-if
not therapists-are cautious. There are indeed people who
neglect the rest
of their lives as they spend every waking moment at the
monitor. But is it
the technology or the be-havior that the technology
enables that peo-ple
are really hooked on? The things people are addicted to
on the Net are the
same things people get hooked on without it: gambling
(including day
trading), pornography, and shopping, notes Marc Pratarelli of
the
University of Southern Colorado in Pueblo. His group is doing factor
analysis of questionnaire responses by computer users to get at the "core
issues" and to determine "if it is in fact just one more fancy tool" to
enable a primary habit.
And what about "positive addictions"? Some
years ago jogging was touted as
one that raised endorphin levels (which in
turn stoke up the dopamine) and
resulted in a "natural high." Although human
behavioral addictions are
difficult if not impossible to model in animals,
Stefan Brené of the
Karolinska Institute in Stockholm, Sweden, thinks he has
done it with
running. He says rats that have been bred to be addiction-prone
spend much
more time on the running wheel than other rats do. Furthermore,
biochemical
tests indicate the impulses both to run and to consume cocaine
are governed
by "similar biochemical adaptations." He also says the work-
most of it as
yet unpublished- shows that in an addiction-prone rat, running
can increase
preference for ethanol- "indicating that a natural, nontoxic .
addiction
can under some instances potentiate the preference for a
drug."
The above by no means exhausts the list of behav-iors that some
sci-entists
see as ad-dictive. And it seems to be true across the board that
having one
addiction lowers the threshold for developing another, says
Walter Kaye,
who does research on eating disorders at the University of
Pittsburgh
Medical Center. Just what form addictions take has a lot to do
with one's
sex, says Pratarelli. Men are overwhelmingly represented among
sex
"addicts" and outnumber women by about 2 to 1 in gambling and substance
abuse; women are prone to what psychiatrist Susan McElroy of the University
of Cincinnati College of Medicine calls the "mall disorders"- eating,
shopping, and kleptomania. (Kim says the ratio of females to males in
kleptomania is 2 or 3 to 1; perhaps 90% of compulsive shoppers are
women.)
To cast more light on the mechanisms of addiction, scientists
have taken a
growing interest in behavior of the brain's reward circuitry in
normal
sub-jects. In a much-cited paper in last May's issue of Neuron, Hans
Breiter of Massachusetts General Hospital in Boston and his colleagues used
fMRI to map the responses of normal males in a roulette-type game of
chance. Blood flow in dopamine-rich areas, the scientists found, indicated
that "the same neural circuitry is involved in the highs and lows of
winning money, abusing drugs, or anticipating a gastronomical treat." Other
research has been showing that many types of rewards besides money-
including chocolate, music, and beauty- affects those reward
circuits.
Shaffer and others in his camp believe that if such a reward is
powerful
enough, it can retrain those circuits in a vulnera-ble person. Not
everyone, however, buys the idea that nondrug stimuli really can be potent
enough to generate what has been traditionally thought of as addiction.
"Many people believe that [only] addic-tive drugs alter the circuitry in
some critical way," says Wise of NIDA. And, he says, drugs are far more
powerful than "natural" rewards, increasing dopamine "two to five times
more strongly." Kaye also warns that the fact that certain disorders share
the same pathways does not necessarily prove they're closely linked. After
all, he notes, "stroke and Parkinson's also involve the same
pathway."
Despite the uncertainties, addiction re-search is "going beyond
the earlier
conceptual framework," says neuroscientist Read Montague of
Baylor College
of Medicine in Houston. "Historically, these definitions have
come out of
animal behavior literature," and addiction has been defined in
terms of
rats frenziedly pressing levers for cocaine. Now, he says, "we need
a
better theory of how the brain processes reward-ing events," one that
involves discovering the "algorithms" people follow that lead them into and
then keep them trapped in their disastrous behaviors.
CONSTANCE
HOLDEN