Wednesday, April 13, 2011
One of the most famous science experiments is the one involving Pavlov and his dog in which Ivan Pavlov conditioned the dog to salivate at the sound of a bell.
Addictive drugs affect the brain in a similar but more powerful way, says Hitoshi Morikawa, a neurobiologist in the Waggoner Center for Alcohol and Addiction Research.
“We think addiction is a form of pathological overlearning in which the brain remembers too much the association between certain environmental stimuli and drug-seeking or drug-taking behaviors,” he said.
Read about Hitoshi Morikawa’s latest research, Alcohol Helps the Brain Remember, Says New Study
For example, ex-addicts who return to their hometowns might find themselves in places where they scored drugs in the past, looking for street dealers, he said.
“It’s like an automatic response to a previously learned stimulus,” said Morikawa, who was a medical doctor before he started his research career.
Such form of stimulus-response association, he said, has been hardwired into brain circuits by dopamine, a transmitter for learning in the brain.
“The synaptic connections that are active when dopamine levels are high will be strengthened more efficiently,” he said. “All addictive drugs are very efficient in elevating dopamine levels in various brain areas because they all directly get into the brain and stimulate the dopaminergic system by their pharmacological actions.”
Morikawa’s laboratory injects drugs into slices of the brains of rats and mice to search for where these interactions are taking place. Electrophysiological recordings and fluorescent imaging are used to see the neuronal activity generated by the drugs.
“We have found, for example, in animals that have been repeatedly exposed to drugs like amphetamine or ethanol that plasticity is dramatically enhanced,” he says. “Which might account for the overlearning of the cues, the environmental stimuli associated with addictive drugs.”
That discovery, in turn, could indicate that there might be a treatment for addiction that would interfere with the learning of drug-associated behaviors.
“Our goal is to provide a powerful pharmacological intervention for addiction,” Morikawa said. “When combined with other treatment modalities such as psychotherapy, this might help addicts unlearn the environments and behaviors related to drugs.”