Prefrontal Cortex Controls Habits
October 30, 2012

Pinpointing Where Habits Find Themselves In Brain

Lee Rannals for — Your Universe Online

Neuroscientists have identified a region of the brain that is capable of switching between new and old habits.

A new study by MIT neuroscientists has found a wall region of the brain's prefrontal cortex 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,” Institute Professor Ann Graybiel, a member of the McGovern Institute for Brain Research at MIT, said in a statement. “However, it doesn´t free up all of it. There´s some piece of your cortex that´s still devoted to that control.”

Graybiel said the study could offer some hope for those people who are trying to break some bad habits.

The study, which was published in the Proceedings of the National Academy of Sciences, shows although habits may be deeply ingrained, the brain's planning centers can shut them off.

The research also raises the possibility of intervening in that brain region to treat people who suffer from disorders like obsessive-compulsive disorder.

The team experimentally simulated the situation with rats trained to run a T-shaped maze. As the rats approached the T, they heard a tone indicating whether they should turn left or right. When they chose correctly, they received a reward.

In order to show the behavior was habitual, the team stopped giving the trained rats any rewards and found they continued running the maze correctly.

Once they had shown the habit was fully ingrained, the team 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 appears to be located in deep brain structures, it has been shown that the IL cortex is also necessary for these behaviors.

The researchers used optogenetics to inhibit specific cells with light, turning 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.

The rats almost instantly dropped the habit of running to the left, suggesting that turning off the IL cortex switches the rats' brains from an "automatic, reflexive mode to a mode that is more cognitive or engaged in the goal," according to Kyle Smith, lead author of the paper.

Once the team was able to break the rats out of the habit of running left, they formed a new habit of running to the right side. They showed they could break this habit by inhibiting the IL cortex with light again.

They found after doing this that rats immediately regained their original habit of running to the left.

“This habit was never really forgotten,” Smith said in the statement. “It´s lurking there somewhere, and we´ve unmasked it by turning off the new one that had been overwritten.”

The findings suggest the IL cortex is responsible for determining 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.

Jane Taylor, a professor of psychiatry and psychology at Yale University, said this study raises ideas concerning how automatic habitual behaviors are.

“We´ve always thought of habits as being inflexible, but this suggests you can have flexible habits, in some sense,” Taylor, who was not part of the research team, said in a statement.

The team is planning to perform follow-up studies to pinpoint exactly where during a maze run the IL cortex selects the appropriate habit. They also are planning to specifically inhibit different cell types within the IL cortex to see which are more involved in habit control.