Neuroscientists identify a brain region that can switch between new and old habits

October 30, 2012 by Anne Trafton

Habits are behaviors wired so deeply in our brains that we perform them automatically. This allows you to follow the same route to work every day without thinking about it, liberating your brain to ponder other things, such as what to make for dinner.

However, the brain's executive command center does not completely relinquish control of habitual behavior. A new study from MIT has found that a small region of the brain's , where most thought and planning occurs, is responsible for moment-by-moment control of which habits are switched on at a given time.

"We've always thought—and I still do—that the value of a habit is you don't have to think about it. It frees up your brain to do other things," says Institute Professor Ann Graybiel, a member of the McGovern Institute for at MIT. "However, it doesn't free up all of it. There's some piece of your cortex that's still devoted to that control."

The new study offers hope for those trying to kick bad habits, says Graybiel, senior author of the new study, which appears this week in the . It shows that though habits may be deeply ingrained, the brain's planning centers can shut them off. It also raises the possibility of intervening in that brain region to treat people who suffer from disorders involving overly habitual behavior, such as obsessive-compulsive disorder.

Lead author of the paper is Kyle Smith, a McGovern Institute research scientist. Other authors are recent MIT graduate Arti Virkud and Karl Deisseroth, a professor of psychiatry and at Stanford University.

Old habits die hard

Habits often become so ingrained that we keep doing them even though we're no longer benefiting from them. The MIT team experimentally simulated this situation with rats trained to run a T-shaped maze. As the rats approached the decision point, they heard a tone indicating whether they should turn left or right. When they chose correctly, they received a reward—chocolate milk (for turning left) or sugar water (for turning right).

To show that the behavior was habitual, the researchers eventually stopped giving the trained rats any rewards, and found that they continued running the maze correctly. The researchers then went a step further, offering the rats chocolate milk in their cages but mixing it with lithium chloride, which causes light nausea. The rats still continued to run left when cued to do so, although they stopped drinking the chocolate milk.

Once they had shown that the habit was fully ingrained, the researchers wanted to see if they could break it by interfering with a part of the prefrontal cortex known as the infralimbic (IL) cortex. Although the neural pathways that encode habitual behavior appear to be located in deep brain structures known as the basal ganglia, it has been shown that the IL cortex is also necessary for such behaviors to develop.

Using optogenetics, a technique that allows researchers to inhibit specific cells with light, the researchers turned off IL cortex activity for several seconds as the rats approached the point in the maze where they had to decide which way to turn.

Almost instantly, the rats dropped the habit of running to the left (the side with the now-distasteful reward). This suggests that turning off the IL cortex switches the rats' brains from an "automatic, reflexive mode to a mode that's more cognitive or engaged in the goal—processing what exactly it is that they're running for," Smith says.

Once broken of the habit of running left, the rats soon formed a new habit, running to the right side every time, even when cued to run left. The researchers showed that they could break this new habit by once again inhibiting the IL cortex with light. To their surprise, they found that these rats immediately regained their original habit of running left when cued to do so.

"This habit was never really forgotten," Smith says. "It's lurking there somewhere, and we've unmasked it by turning off the new one that had been overwritten."

Online control

The findings suggest that the IL cortex is responsible for determining, moment-by-moment, which habitual behaviors will be expressed. "To us, what's really stunning is that habit representation still must be totally intact and retrievable in an instant, and there's an online monitoring system controlling that," Graybiel says.

The study also raises interesting ideas concerning how automatic habitual behaviors really are, says Jane Taylor, a professor of psychiatry and psychology at Yale University. "We've always thought of habits as being inflexible, but this suggests you can have flexible habits, in some sense," says Taylor, who was not part of the research team.

It also appears that the IL cortex favors new habits over old ones, consistent with previous studies showing that when habits are broken they are not forgotten, but replaced with new ones.

Although it would be too invasive to use optogenetic interventions to break habits in humans, Graybiel says it is possible the technology will evolve to the point where it might be a feasible option for treating disorders involving overly repetitive or addictive behavior.

In follow-up studies, the researchers are trying to pinpoint exactly when during a maze run the IL cortex selects the appropriate habit. They are also planning to specifically inhibit different cell types within the IL , to see which ones are most involved in habit control.

Explore further: Brain rhythms are key to learning

Related Stories

Brain rhythms are key to learning

September 27, 2011

Neuroscientists have long known of the existence of brain waves — rhythmic fluctuations of electrical activity believed to reflect the brain’s state. For example, during rest, brain activity slows down to an alpha ...

Recommended for you

Umbilical cells help eye's neurons connect

November 24, 2015

Cells isolated from human umbilical cord tissue have been shown to produce molecules that help retinal neurons from the eyes of rats grow, connect and survive, according to Duke University researchers working with Janssen ...

Brain connections predict how well you can pay attention

November 24, 2015

During a 1959 television appearance, Jack Kerouac was asked how long it took him to write his novel On The Road. His response – three weeks – amazed the interviewer and ignited an enduring myth that the book was composed ...

No cable spaghetti in the brain

November 24, 2015

Our brain is a mysterious machine. Billions of nerve cells are connected such that they store information as efficiently as books are stored in a well-organized library. To this date, many details remain unclear, for instance ...

Neurons encoding hand shapes identified in human brain

November 23, 2015

Neural prosthetic devices, which include small electrode arrays implanted in the brain, can allow paralyzed patients to control the movement of a robotic limb, whether that limb is attached to the individual or not. In May ...

Wireless sensor enables study of traumatic brain injury

November 23, 2015

A new system that uses a wireless implant has been shown to record for the first time how brain tissue deforms when subjected to the kind of shock that causes blast-induced trauma commonly seen in combat veterans.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.