Traditional views of what motivates addictive behavior, such as hedonistic pleasure seeking and avoidance of aversive withdrawal symptoms, have been repeatedly demonstrated as insufficient and illogical. New directions in addiction research continue to challenge traditional assumptions about drug abuse.
According to APS Fellow and Charter Member Terry E. Robinson, University of Michigan, previous assumptions do not account for the “dissociation” between what he names the “wanting” and the “liking” of the drug by the addict. Robinson’s invited address “The Psychology and Neurobiology of Addiction,” was presented at the APS Annual Convention in Atlanta and sponsored by the National Institute on Drug Abuse.
He reminded his audience early in his talk that even though many people try or use drugs, most are not addicts. There is a difference between use and compulsive use.
Robinson theorizes that through repeated exposure to the drug of abuse, persistent neuroadaptations are produced. Specifically, the changes occur in the brain regions usually associated with reward, leaving the addict particularly sensitive and therefore vulnerable to relapse even long after drug use has discontinued. Like the Alcoholics Anonymous cliché, “when you are in the AA rooms [meetings], your addiction is out in the parking lot doing push-ups.” These changes on the neural level can be observed clinically as an increase in compulsive drug-seeking and taking behavior.
Robinson provided compelling evidence for the psychomotor sensitization, incentive-sensitization, and neural sensitization components of the path. Psychomotor sensitization is an increase in psychomotor activity with the same dose of a drug. It was demonstrated to have persisting effects, up to one year in animals. Robinson expressed his own sensitivity to us all when he quipped, “A year is a long time in a rat’s life, in fact, a year is a long time in a graduate student’s life!” Incentive-sensitization is an increased sensitivity to the drugs’ effect on motivation. Neural sensitization is actual neuroanatomical change.
Robinson provided data from several labs and explained the fundamentals of measuring the length of dendritic trees, counting the number of branches, and then the number of synaptic spines on each branch. It is at this most detailed level that the drugs of abuse make their enduring changes. “A fundamental rewiring, we think, of the brain occurs in the addict,” he said.
Robinson then turned this argument on its heel. This altered brain in “drug-experienced” individuals is not inevitable he said, but rather “powerfully modulated by the environment.”
After exploring the classic “nature versus nurture argument,” Robinson and his colleagues showed results which imply that context is of utmost importance in relapse for addicts, suggesting set and setting of drug use are indeed part of a complex matrix of psychological factors that can ultimately change the brain.
According to Robinson, the next frontier of science is in the area of gene expression. He is exploring how the environment controls drug expression on brain change. So far he suggests, “depending on where you take drugs you engage different cells … and other portions of this circuit … the environment is modulating in a dramatic manner at the level of gene expression.”