BY BETH AZAR
page 74
Conditioning--the
workhorse of psychology made famous by Pavlov and his team of
dogs--has long impressed psychologists with its power to dramatically
shape animal as well as human behavior. Now, a new study shows
conditioning may also encourage people to start taking a drug
they initially reject.
Five of six participants
in the study, published in the May issue of the APA journal
Experimental
and Clinical Psychopharmacology (Vol. 10, No. 2), switched
their preference from a sugar pill to a capsule filled with
diazepam (Valium) after researchers surreptitiously paired the
drug with a bigger monetary payoff than the placebo. The effect
was so strong, it made up for the study's small sample size,
says University of California, Los Angeles, psychologist John
Roll, PhD, who conducted the study with colleagues at Wayne
State University.
And the implications
of the findings could be significant, he says. They indicate
that people may be more likely to continue taking a drug if
it's paired with a positive experience, even if the first encounter
with the drug is unpleasant. And such pairings are common: For
example, teens often smoke marijuana in highly social settings,
and some people take amphetamines to accompany sexual experiences.
The study "nicely
remind[s] us that drug ingestion by humans takes place in a
rich and dynamic environment that provides many different opportunities
for learning," writes University of Vermont psychopharmacologist
Mark Bouton, PhD, in one of several commentaries accompanying
the article.
That said, this
particular study is just one step in proving that conditioning
per se is at work encouraging people to take diazepam or any
other drug, adds Bouton. Several other explanations are equally
plausible, including the idea that people simply grow to enjoy
the effects of the drug over repeated exposure.
Your choice:
sedative or sugar pill?
The Experimental
and Clinical Psychopharmacology study consisted of two phases
of nine sessions each with each session lasting about five-and-a-half
hours with at least 48 hours between sessions. At the beginning
of the first four sessions of phase one, the researchers gave
participants a capsule containing either a placebo or diazepam,
alternating between the two so that each participant sampled
the placebo twice and diazepam twice. Except for brief encounters
with the researchers, participants lounged in a room filled
with games, books and videos for the remainder of the session.
The next five sessions
of phase one were exactly the same, except participants could
freely choose between the two capsules they'd taken in the previous
sessions. As expected from earlier research, most participants--five
of six--chose the placebo on every trial. The ones who didn't
chose diazepam every time.
Phase two was similar
to phase one, but instead of being idle during the first four
sessions, participants completed two computer tasks every half-hour
beginning 30 minutes before they ingested the capsule and ending
two hours after. Researchers told them that they would earn
extra money based on their performance on these tasks, and at
the end of each set of tasks the computer displayed how much
they had earned.
In reality, how
much money participants earned was not linked to their performance.
Instead, the researchers programmed the computer to pay participants
less--an average of $10.13--when they ingested the drug they
preferred during the choice sessions of phase one (placebo for
five of six participants and diazepam for one) and more--an
average of $20.41--when they ingested the drug they rejected
during those sessions. In effect, participants got surreptitiously
rewarded for taking diazepam.
To help mask the
fact that the amount of money people earned was linked to drug
choice rather than performance, the researchers used computer
tasks in which people find it difficult to gauge their own performance.
The last five sessions were exactly the same as in phase one
with participants allowed to choose which capsule to take and
then left to their own devices for the majority of the session.
All five participants
who had preferred placebo during phase one of the study preferred
diazepam during phase two once it was linked with more money
than taking the placebo. Indeed, while participants chose placebo
on 83 percent of occasions during phase one, they chose it on
only 13 percent of occasions during phase two, choosing diazepam
87 percent of the time. The only participant who didn't change
his preference from phase one to phase two was the one who preferred
diazepam in the first round. In phase two, he stuck with his
preference.
Interestingly,
pairing money with the drug not only appeared to affect which
drug people chose to take, it also affected how the drug made
them feel. During phase one of the study, the five participants
who preferred placebo reported that it was more pleasurable
than diazepam. After the researchers paired diazepam with a
higher payoff in phase two, however, the same people reported
feeling better after taking diazepam.
What about the
one participant who defied the trend and chose diazepam consistently
throughout the study? It's possible, the researchers say, that
for this one participant, diazepam was a strong enough temptation
from the beginning to override any reinforcement of money. "It
may be that once the pharmacology of a drug is working as a
reinforcer, other influences have less of an effect," says Roll.
That's why he thinks this type of conditioning might be strongest
when people are first experimenting with drugs.
Questioning
the mechanism
As for the majority
who did shift their preference from placebo to diazepam in phase
two, the researchers propose conditioning is responsible. After
pairing diazepam with extra money during the first four sessions
of phase two, the drug acquired the properties of a conditioned
reinforcer, they say. That is, people unconsciously associated
the drug with more money, thereby making it more appealing than
it normally would be. The study is one of the first to show
that people can be conditioned to have a preference for a drug,
says Roll. "We suggest the mechanism is conditioned reinforcement,"
he adds.
But there may be
other equally plausible mechanisms at work, suggest Bouton and
Concordia University's Jane Stewart, PhD, who also wrote a commentary.
For example, says Stewart, it may be that diazepam had a different--and
perhaps more pleasurable--physiological effect on participants
during phase two when they were engaged in the computer tasks.
"If this were the
case," she writes, "then the change in drug choice would not
arise from associating some fixed pharmacological effect of
the drug with a rewarding state of affairs; rather, the different
subjective effects of the drug in the two conditions could be
attributed to the differential effects of the drug on the brain."
Roll and his colleagues
admit their study does not rule out alternative explanations.
That's why they're continuing with this same line of research.
Next, they will see if they can use the same paradigm to get
people to switch from preferring a pleasurable drug, such as
an amphetamine, to preferring a placebo. They also hope to use
these studies as a model for designing laboratory-based studies
of ways to prevent drug use.
That said, if this
study's preliminary findings hold up and a drug can become a
conditioned reinforcer, there are "profound" implications for
drug abuse research, write Roll and his colleagues. "Consider
how often a drug is introduced to someone in the context of
other sources of powerful reinforcers," they write. "For example,
methamphetamine is often used among certain groups of individuals
to facilitate sexual activity."
Even more common,
people use alcohol and tobacco in bars to "loosen" up and are
rewarded with meeting people. Teens use psychoactive drugs as
an inroad to forming friendships. And people who use caffeine
to wake up may find their behavior becomes reinforced when they're
more successful at early-morning meetings.
In some sense,
says Roll, people get a "double whammy": Added to the pleasurable
effects of the drug is a sexual encounter, a friendship made
or a point scored at work--powerful reinforcers all on their
own. Particularly for someone using the drug for the first time,
such a pairing may make the drug more appealing than it would
have been by itself and thereby increase the likelihood the
person will use the drug again.
Beth Azar is a writer
in Portland, Ore.