The Heart of Addiction

How psychology drives addictive behavior.

When Mice Are Men and When They're Just Mice

Be careful what you believe.

A recent report about creating stem cells from ordinary tissue in mice created a great deal of scientific excitement as a possible medical breakthrough for treating human illnesses (though there is now some doubt about its findings). Scientists routinely study mice and rats, not out of a deep interest in rodents, of course, but because we and they are mammals, so we share a good deal of biology. And sometimes the rodent findings work fine for humans, sometimes not. A well-known example from the 1990's was the huge optimism that cancer would soon be cured because of the work of Dr. Judah Folkman with mice. His approach (angiogenesis inhibition) basically stopped cancer in its tracks. A modest man, when questioned about the applicability of his work to humans, he famously demurred, saying ”If you’re a mouse and you have cancer, we can take good care of you.” As it turned out, he was right to be cautious; his approach did not cure cancer in humans.

It makes sense to experiment with rodents before trying ideas in humans. But it is a serious scientific error to generalize these results to humans unless they can be shown to apply to our species. Sadly, this is just the kind of very bad science that has taken over the addiction field. Neurobiological researchers have claimed for years that rat behavior to seek drugs is the same as human addiction, without the slightest awareness of how different that is from human addiction. Indeed, of all the ways one should not generalize from rats to people, complex behavior is the most obvious, since the one way that we are least like rats is that we have giant brains capable of human psychology, while rats have brains the size of a pea.

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It is true that we share the more primitive parts of our brains with other mammals, and that includes the mammalian reward pathway that is central to the neurobiological view of addiction. But if we were driven simply by reward-seeking caused by release of a neurotransmitter (dopamine), as is the case for rats, we would no longer be human. Rats scurry about looking for drugs when excited by the brain stimulation the researchers found. Humans with addictions plan their behavior, often hours or even days in advance. Humans also shift behavior away from drug use to non-drug compulsive acts like gambling, shopping or cleaning. The fact is that if the "brain disease" theory that applies to rats were actually true in humans, there would be no civilization. We would be controlled by our dopamine releases and would run around doing whatever our neurotransmitters demanded. We would act like rats.

Of course, we know the "brain disease" theory is wrong for other reasons, since there are literally millions of examples of humans who have taken high doses of drugs like heroin and alcohol who never become addicts, something that should be impossible according to the "brain disease" theory.

Why do we accept such false ideas? Part of the answer is that we trust scientists to be careful with generalizing their results beyond what they have actually studied. And most scientists, like Dr. Folkman, are very careful to avoid that mistake. Another part of the problem is that we trust organizations that we believe have carefully vetted scientific information before endorsing it. Yet, there are some such groups that have simply endorsed the reductionistic brain disease idea without having done any independent study of their own, or even considered the error with such generalizations.

The mistake of thinking human addiction is the same as rat stimulation is a cautionary tale. We all need to question what we hear, even from people who are supposed to know what they're talking about, until we have independent scientific review from scientists besides those invested in their own views.

Lance Dodes, M.D., is an assistant clinical professor of psychiatry at Harvard Medical School.

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