Recovering heroin addicts may lose their inner voice

We talk to ourselves all day, whether it's convincing ourselves to get out of bed, or avoid that second piece of cake. But this internal voice uses a lot of brainpower. People who have to concentrate on resisting an addiction appear to sacrifice this ability in order to conserve brainpower for other tasks.

The average person can juggle about four mental tasks at any time, says Monica Faulkner of Johns Hopkins University in Baltimore. How much you can multitask is related to working memory.

With the assumption that recovering addicts must think constantly about their addiction, Faulkner and her colleagues wondered whether this comes at the cost of using up one of those four "slots", possibly impairing their overall working memory.

Faulkner and Cherie Marvel, also of Johns Hopkins, recruited six people who had never used drugs and six recovering from a heroin addiction who were taking methadone to help. They showed the volunteers an image, either of a word, a Chinese character, or a pattern. They then waited six seconds, and showed the volunteers a second image. During those six seconds, the researchers recorded the volunteers' brain activity using functional magnetic resonance imaging (fMRI). The volunteers' task was to press a button if the second image matched the first.

The people recovering from addiction took a few hundred milliseconds longer than the controls to determine whether they had seen the images previously. But the more interesting result came from the pattern of activity in their brains throughout the 6 second window.

The part of the motor cortex that controls speech and introspection appeared to be working particularly hard if the first image was of a word. By contrast, it wasn't nearly as active if they were trying to remember a first image that was either a pattern or a Chinese character.

Hearing hallucinatory voices

"The differences are subtle," says Marvel. It's not that they can't remember words, she says, but the results suggest that those recovering from addiction require more effort to do so. That might indicate that these people are less able to rely on an internal monologue that repeats the word to keep it in the working memory.

Another brain region worked hard during the 6 second window: the anterior insula. This region has been invoked in the ability to pay attention to one's own internal state, and linked to hearing hallucinatory voices. (Cerebral Cortex, DOI: 10.1093/cercor/bhp079)

"It's an elegantly designed study," says Steven Grant of the National Institute on Drug Abuse in Bethesda, Maryland. There's growing evidence that substance abusers have cognitive difficulties when distracted from their internal state, he says, and this may have implications for how addiction should be treated.

One complicating factor is that the people recovering from addiction were all taking methadone. The drug has never been shown to impair working memory, Marvel says, but they plan to test whether those recovering from addiction without taking methadone have similar differences in their verbal working memory.

Either way, the effect might help to explain why recovery from addiction is so difficult, Faulkner says, as it could be hard for addicts to talk themselves out of social situations where they'd be likely to relapse.

The researchers presented their results results at the Society for Neuroscience meeting in New Orleans last week.

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