ANN ARBOR—For addicts to obtain drugs, such as cocaine, it often requires considerable ingenuity and flexibility—behavior that should not be described as habit, according to a new study.
The addictive behavior is fueled by motivation in the face of adverse consequences and constantly changing circumstances, say researchers at the University of Michigan and The Open University in England.
The researchers studied how male rats solved increasingly difficult puzzles to receive a cocaine reward. This concept differs from other studies in which rats and other animals repeat the same behavior, such as pressing a lever or poking their noses through a port, to get the drugs.
Since the puzzles always changed after weeks of testing, the rats' addiction-like behavior never became automatic or habitual, the researchers said.
"We're challenging the definition of addiction as a habit," said Bryan Singer, the study's lead author and former U-M psychology researcher who is now at The Open University,
Brain regions that were important for regulating habits were not involved in drug-seeking.
"Instead, other brain regions critical to motivation controlled drug-seeking in our rats," said Singer, who collaborated with U-M researchers Monica Fadanelli, Alex Kawa and Terry Robinson.
The rats occupied chambers with puzzles, and they had to perform (in specific orders) tasks that included spinning a wheel, pressing a lever and poking their nose into a hole. If they made mistakes in trying to solve a puzzle, the animals had to restart from the beginning.
Successfully completing a puzzle allowed the rats to self-administer small doses of cocaine. Over the course of the experiment, the rats continued solving the challenging puzzles, the study showed.
"The rats' perseverance in drug-seeking,and increased rate of responding reflect the increasing motivation to obtain the drug," said Robinson, the Elliot S. Valenstein Distinguished University Professor of Psychology and Neuroscience at U-M. "And because they adjusted their behavior, it never became habitual."
The findings appear in the current issue of the Journal of Neuroscience.