Even when a cocaine abuser is not aware of briefly seeing a drug-related image, such a picture can instantaneously activate the emotion and reward circuits in the brain. Quick views of sexual images also activate many of the same brain areas. That pattern of activity may be "the brain's primordial signature for desire," according to Drs. Anna Rose Childress and Charles O'Brien and colleagues at the University of Pennsylvania.
In a study with 22 men seeking treatment for cocaine abuse, the researchers demonstrated that the participants' brains responded to images outside their conscious awareness. The researchers used a technique in which a target picture, which featured either sexual or drug-related imagery, was flashed for 33 milliseconds, followed by a gray screen and then a 467-millisecond presentation of a neutral picture.
Participants reported remembering the neutral pictures, but not the target pictures. Nevertheless, activity in their neural circuits increased in response to the target images.
The researchers did not determine whether participants felt a surge in craving after viewing the subliminal pictures. Cocaine abusers' rapid neural response to reward cues outside awareness may signify vulnerability to relapse, the researchers suggest.
JPLoS ONE 30;3(1):e1506, 2008. [Full Text (PDF, 213KB)]