February 4, 2008

Subconscious Signals Can Trigger Brain’s Drug-Craving Centers

Photo of an upset man

Quick flashes of cocaine-related photos—so brief viewers don’t even realize what they’re seeing—can instantly trigger “reward circuitry” in the brains of drug-addicted patients, activating the same brain regions that respond to sexual images. Researchers say their findings may provide new clues for treating addictions and possibly other conditions, like eating disorders, that are marked by uncontrolled desires and behaviors.

The idea that we’re often motivated by unconscious fears and desires has been around for more than a century, but it’s been difficult for scientists to determine how such unconscious factors affect the brain. In a new study, a research team led by Drs. Anna Rose Childress and Charles O’Brien at the University of Pennsylvania School of Medicine used neuroimaging to look at how specific brain regions respond to different types of unconscious cues. Their research, funded by NIH’s National Institute on Drug Abuse (NIDA), was published in the June 30, 2008, issue of the journal PLoS One.

The scientists used functional MRI to scan the brains of 22 men—all under treatment for cocaine addiction—while they viewed a series of images. Test images flashed by in just 33 milliseconds—so quickly that the patients were not consciously aware of them. The images included drug-related visuals—like crack pipes or chunks of cocaine—as well as sexual, disturbing and neutral images. Each test image was immediately followed by a longer view—lasting nearly a half-second—of a neutral image, such as household objects or outdoor scenes. Although patients could consciously recall only the longer-lasting images, their brain scans revealed responses to the “unseen” test images.

The unseen drug photos stimulated reward circuits within the brain’s limbic system, a primitive network involved in emotion and reward and also implicated in drug-seeking and craving. These activated brain regions overlapped substantially with those activated by sexual images. This finding supports the idea that addictive drugs take over the brain’s reward circuits that normally respond to cues for natural rewards needed for survival, like food and sex. 

To verify that the brain’s responses to unseen drug cues reflected the patients’ conscious feelings about drugs, some of the volunteers were given a different test 2 days later. They were asked to take a longer look at some of the test images, and their emotional responses were assessed. Those with the strongest brain responses to unseen drug cues in the earlier test also had the strongest positive associations to these visible drug cues.

“This is the first evidence that cues outside one’s awareness can trigger rapid activation of the circuits driving drug-seeking behavior,” said NIDA Director Dr. Nora Volkow. “Patients often can’t pinpoint when or why they start craving drugs. Understanding how the brain initiates that overwhelming desire for drugs is essential to treating addiction.”

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