Mouse Experiment Sheds Light On Why We Obey Habits

It involves the same brain system that responds to marijuana

A man smokes a cigarette

A man smokes a cigarette

Scientists are unraveling why we form habits. This knowledge could help people who have trouble breaking them.Flickr user Petras Gagilas

Our days are filled with little habits, like preparing coffee, locking the door, or driving to work. Habits let us act efficiently, following a trusted routine instead of planning out each move. But we’re flexible enough to adapt when circumstances change—if the road we normally take on our way to the office is closed, we can figure out an alternate route.

A recent study published May 26 in the journal Neuron might help explain how this shift, from acting out of habit to coming up with a goal and pursuing it, happens. We act of out habit when chemical messengers called endocannabinoids dampen activity in a certain part of the brain. In the experiment, mice that were unable process endocannabinoids were less likely to act based on habit.

Endocannabinoids are built along similar lines to THC, the active ingredient in marijuana. They influence brain areas involved in pleasure, memory, and concentration, among other things (which are thrown off kilter when THC docks into ports, or cannabinoid receptors, meant for endocannabinoids).The researchers note that work in mice indicates that "chronic" use of THC actually causes the brain to depend more on habits when solving problems, instead of coming up with new strategies.

Previously, the team had found that a part of the brain called the orbitofrontal cortex is involved in purposeful behavior. Other work has also indicated that endocannabinoids are somehow involved in learning habits.

For the new experiment, the group modified mice so their neurons were missing the cannabinoid receptors that accept endocannibinoids in this area.

Then they trained the rodents on two tests that required them to press levers to get a snack. In one, the pellets were delivered after a certain, ever changing number of hits. Whenever the mice felt like it, they could fiddle with the lever, knowing that eventually it would deliver the jackpot.

In the other, the mice could only access the pellets after a certain amount of time (which also kept changing) had passed. In this second scenario, mice tend to develop a habit, checking on the lever to see if it’s snack time.

So far, the regular and modified mice act the same way. The scientists then mixed things up by offering the mice their treat instead of normal chow beforehand. This makes the animals less motivated to bother pressing the lever for more treats.

At this point, normal mice expended less effort on the first snack test, in which a snack is guaranteed. On the other, in which they had built a habit, their lack of motivation didn’t stop them.

But the mice that were short a few cannabinoid receptors pawed at the lever fewer times on both tests. When they were less keen on their snack, their habit dissolved.

The results of the study indicate that people with disorders such as obsessive-compulsive disorder and addiction, which make it difficult to break ​destructive habits, might benefit from treatments that target the endocannabinoid system. ​This would mean developing ways to stop people’s endocannabinoid receptors from acting.​