You might associate addiction with habits; it’s hard to stop doing something if it’s part of your routine, and doing something habitually can transform it into an addiction. But new research shows there is more to addiction than once thought.

Researchers at the University of Michigan studied male rats, giving them complicated puzzles for a reward of cocaine. The puzzles changed each week, meaning the rodents never developed one repeated action that could become a habit.

The puzzles involved spinning a wheel, pressing a lever and putting their noses inside a hole. If the rats made one mistake, they had to start all over again. But the rats were consistent in their attempts to get the cocaine.

“We’re challenging the definition of addiction as a habit,” said Bryan Singer, lead author and former psychology researcher at the University of Michigan. He is now at the Open University in the UK.

Brain regions linked to regulating habits were not involved when the rats tried to get the drug. “Instead, other brain regions critical to motivation controlled drug-seeking in our rats,” said Singer.

For the duration of the experiment, the rats continued solving the difficult puzzles, the study, published in the Journal of Neuroscience, shows.

“The rats’ perseverance in drug-seeking, and increased rate of responding reflect the increasing motivation to obtain the drug,” said Terry Robinson, professor of psychology and neuroscience. “And because they adjusted their behavior, it never became habitual.” They concluded that habitual drug-seeking isn’t necessary for the development of addiction-like behaviour.

The team hopes the research will be useful in studying addiction in humans in the future. By looking at the changes that occur in the brain when addiction takes hold, the team thinks it might be possible to stop the transition.