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Monday, 19 November 2012 18:24

How the brain forms habits

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People act on habits automatically because the habits are deep inside our brains. This explains why we take the same route to work every day, or put our left shoe on first. It also allows our brains to think about what to make for dinner, or what to wear to school.

The brain's administrative command center, however, does not fully renounce control of constant behavior. The new study has determined that a small region of the brain's prefrontal cortex has been identified as the controller of minute-by-minute control of thinking and acting, and can be prompted on at any moment.

Ann Graybiel, from the McGovern Institute for Brain Research at MIT said:

"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. It frees up your brain to do other things. However, it doesn't free up all of it. There's some piece of your cortex that's still devoted to that control."



Graybiel explained that the recent evidence, published in the Proceedings of the National Academy of Sciences, provides hope for people who cannot seem to shake their bad habits, because it reveals that even though habits are deep in our brains, the brain's control center has the capability of turning them off.

The new findings also pave the way for possible intervention into that area of the brain in order to help people who are affected by certain kinds of conditions which stem from this part of the brain, including OCD (obsessive compulsive disorder).

According to the report, which was led by Kyle Smith, a McGovern Institute research scientist, habits become such a large part of who we are that it sometimes seems it may be virtually impossible to say goodbye to them, even when they may not be good for us.

For their study, the authors conducted an experiment on mice that were trained to run a maze in the shape of a T. When the rats headed toward the part of the maze where they had to make a decision in direction, the researchers played a tone telling them to either go right or left. When the rats went in the correct direction (left), they were given a reward - chocolate milk. When the rodents headed in the wrong direction (right), they were only given sugar water.

To demonstrate that the rats' behavior was consistent, the authors ceased giving the trained rats any rewards, and the animals continued to find their way through the T-shaped maze. Then, after a while, the experts rewarded the rats with chocolate milk again. However, this time it was mixed with lithium chloride, which caused the rats to be nauseated. Even after the nausea, the rats continued to run the maze in the same way they had before, but they stopped drinking the chocolate milk.

When the researchers had determined that the rats' behavior was completely fixed, they wanted to find out if they could change the way the rats were going through the maze by changing a part of the prefrontal cortex called the infralimbic (IL) cortex. The IL cortex plays a role in the development of habits, even though neural pathways which encode habitual continuous behavior are found deep down inside brain structures called the basal ganglia.

Scientists used a method called optogenetics to get inside certain cells with light, and were able to shut off the IL cortex activity for the seconds before the rats approached the part of the maze where they had to make a decision to turn right or left.

The rats almost immediately stopped their habit of turning left and turned to the right instead. This showed that switching off the IL cortex changed the rats from instantly following their habits, and to instead, go the way they thought was right.

After the rats stopped going left, they began turning to the right every single time they were put in the T-shaped maze, even when the experts prompted them to turn left, indicating that a new habit had formed.

Smith said: "This habit was never really forgotten. It's lurking there somewhere, and we've unmasked it by turning off the new one that had been overwritten." The findings clearly indicate that the IL cortex is capable of changing habitual "moment-to-moment" behavior.

Graybiel concluded: "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."

The research brings up questions regarding whether habitual behaviors are really automatic. Jane Taylor, a professor of psychiatry and psychology at Yale University said: "We've always thought of habits as being inflexible, but this suggest you can have flexible habits, in some sense."

The IL cortex seems to favor new habits above old ones, which has been shown in previous studies which indicated that habits are not just thrown out, but replaced by new ones.

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