Scientists examine ways to measure addictive cravings

A new emphasis is put on a phenomenon that had been considered subjective.

By Beth Azar
Monitor staff

Although most clinicians and researchers agree that cravingprobably plays an important role in drug and alcohol addiction, most have avoided studying the phenomenon because it?s simply too hard, said Edward Singleton, PhD, co-chair of APA?s 1998 Annual Convention symposium 'Craving and cognition in the addictions?marriage, separation or divorce?'

Behavioral researchers have long been reluctant to study craving because they considered it subjective and poorly defined, said the session?s other co-chair, Jack Henningfield, PhD, vice president of Pinney Associates in Bethesda, Md. Besides, it?s difficult to separate craving from other issues related to whether an addict uses a drug or not, such as availability, peer pressure and emotional state. Regardless, the National Institute on Alcohol Abuse and Alcoholism (NIAAA) and the National Institute on Drug Abuse (NIDA) have recently put a new emphasis on the issue of craving. And they?re dragging researchers, kicking and screaming, into the arena, said Henningfield, a former NIDA researcher.

'Behavioral researchers have precisely the sort of training necessary to bring objectivity and science to the understanding of this clinically important phenomenon,' he said.

The symposium was part of the NIAAA miniconvention co-sponsored by NIAAA and APA divisions 28 (Psychopharmacology and Substance Abuse) and 50 (Addictions). The researchers who spoke touched on everything from validating a measure for craving to links between craving and drug use to a possible model of how craving works in the brain.

The research to date confirms that drug addicts experience craving through a complex combination of social and personal cues. But it?s still unclear whether craving leads to drug taking, said discussant Maxine Stitzer, PhD, of the Johns Hopkins School of Medicine.

Defining urges

Before researchers can begin to study craving and how it affects drug and alcohol use, they need to have a valid and consistent tool with which to measure it, said Stephen Heishman, PhD, a researcher in NIDA?s intramural research program. He and his colleagues have begun fine-tuning and validating the Questionnaire on Smoking Urges (QSU), a measure of tobacco craving first developed in the early 1990s. The original measure has been used in groups of college students, but never in hard-core drug-abusing populations, said Heishman.

They found that the QSU works just as well in a group of people who use multiple drugs as in the college students, said Heishman. Eighteen hours of tobacco deprivation significantly increased QSU scores among study participants. And smoking two cigarettes reduced QSU scores back to baseline. 'We appear to have a valid tool that researchers can use consistently across studies with varied populations,' said Heishman.

He and his colleagues have also manipulated tobacco craving in a group of drug addicts using audiotaped scenarios of people urging them to smoke. The audiotapes were particularly powerful if they had a negative tone. In addition, the more the addicts craved tobacco, the more they also craved their drug of choice?mostly marijuana and cocaine?indicating a possible link between craving for one drug and craving for another.

Drug craving may also influence drug taking in people trying to quit cocaine, find Singleton and his colleagues at Johns Hopkins and NIDA. But it?s not a clear-cut relationship where craving equals drug taking. Instead, there seems to be a complex interplay between personal and situational cues, such as mood and peer pressure, drug craving and use.

The most common situations that produce cocaine craving are a person?s mood; people, places and things; social pressures; being in a situation where cocaine is the focus; and work situations, said Singleton.

Situational focus on cocaine and mood are the strongest predictors of subsequent cocaine use and are highly correlated with a type of craving called emotionality, which is related to the desire to reduce negative mood, said Singleton. Subsequent use is also moderated by use of cocaine during the previous week.

'Among quitters, cocaine craving seems to be a mixture of urges and desires in the anticipation of the relief from negative affect and withdrawal symptoms, and anticipation of the positive aspects of cocaine use,' said Singleton, who is with The MayaTech Corporation in Silver Spring, Md. In turn, each of these aspects is linked to specific cues and situations.

However, the researchers also find that some people report high levels of emotional craving but refrain from using drugs. 'They seem to be coping,' said Singleton. The next step is to figure out how, and that will likely come only after researchers develop complex computational models that can elucidate the true nature of drug use, craving and cues, said Singleton.

Craving and the brain

Some researchers have turned to brain imaging to examine the brain circuits at work during craving. They find that drug-related cues may cause craving by stimulating memory and attention pathways in the brain. Steven Grant, PhD, Edythe London, PhD, and David Newlin, PhD, of NIDA?s intramural research program, used positron emission tomography (PET) to examine how the brains of 13 cocaine addicts respond to objects designed to stimulate cocaine craving. And they compared these brain scans to scans from five people who had never used cocaine.

During the study?s first week, researchers injected participants with a radioisotope that allows PET to image the brain?s energy use. During the 30 minutes it takes for the brain to fully absorb the isotope, participants watched a videotape related to arts and crafts and viewed art-related objects such as a paintbrush, a pencil and paper. The second week was identical to the first except participants watched a video about cocaine use and examined cocaine-related items, such as a crack pipe, a small amount of cocaine on a mirror and a $10 bill.

Cocaine cues, as opposed to the neutral art cues, increased craving in the cocaine addicts. Also, the cocaine abusers showed increased brain activity in areas associated with attention and memory. No such increases were seen in the non-cocaine users.

The pattern of brain activity in the cocaine users during exposure to the cocaine-related items implies that they were hyper-attending to the stimuli, to the exclusion of anything else, said Grant. And the increased activity in the medial orbital lobe?an area associated with emotionality as well as decision-making and the ability to judge relative risk and long-term gains and losses?suggests that cocaine cues may bias decision-making.

As for craving, Grant and Newlin found that some of their cocaine-using participants didn?t report increases in craving. When they compared the cravers with the non-cravers, they found that the cravers had increased activity in the dorsolateral prefrontal cortex, amygdala and cerebellum. The amygdala might be important in giving an object its 'emotional oomph' by rating it as 'good' or 'bad,' said Grant.

Stitzer was fascinated to see the data showing that craving might activate memory circuits. From her own work on craving, she?s theorized that craving is the result of memories and thoughts triggered by stimuli in the environment. But from all the data currently available, it?s still unclear whether craving itself leads to drug taking, she added. It may be that craving isn?t a good predictor of immediate behavior, but instead predicts eventual relapse: 'Craving level now may be a good predictor of relapse later?in other words, a good predictor over longer time periods,' said Stitzer.