How we form habits and change existing ones

Much of our daily lives are taken up by habits that we’ve formed over our lifetime. An important characteristic of a habit is that it’s automatic— we don’t always recognize habits in our own behavior. Studies show that about 40 percent of people’s daily activities are performed each day in almost the same situations. Habits emerge through associative learning. “We find patterns of behavior that allow us to reach goals. We repeat what works, and when actions are repeated in a stable context, we form associations between cues and response,” Wendy Wood explains in her session at the American Psychological Association’s 122nd Annual Convention.

What are habits?

Wood calls attention to the neurology of habits, and how they have a recognizable neural signature. When you are learning a response you engage your associative basal ganglia, which involves the prefrontal cortex and supports working memory so you can make decisions. As you repeat the behavior in the same context, the information is reorganized in your brain. It shifts to the sensory motor loop that supports representations of cue response associations, and no longer retains information on the goal or outcome. This shift from goal directed to context cue response helps to explain why our habits are rigid behaviors.

There is a dual mind at play, Wood explains. When our intentional mind is engaged, we act in ways that meet an outcome we desire and typically we’re aware of our intentions. Intentions can change quickly because we can make conscious decisions about what we want to do in the future that may be different from the past. However, when the habitual mind is engaged, our habits function largely outside of awareness. We can’t easily articulate how we do our habits or why we do them, and they change slowly through repeated experience. “Our minds don’t always integrate in the best way possible. Even when you know the right answer, you can’t make yourself change the habitual behavior,” Wood says.

Participants in a study were asked to taste popcorn, and as expected, fresh popcorn was preferable to stale. But when participants were given popcorn in a movie theater, people who have a habit of eating popcorn at the movies ate just as much stale popcorn as participants in the fresh popcorn group. “The thoughtful intentional mind is easily derailed and people tend to fall back on habitual behaviors. Forty percent of the time we’re not thinking about what we’re doing,” Wood interjects. “Habits allow us to focus on other things…Willpower is a limited resource, and when it runs out you fall back on habits.”

How can we change our habits?

Public service announcements, educational programs, community workshops, and weight-loss programs are all geared toward improving your day-to-day habits. But are they really effective? These standard interventions are very successful at increasing motivation and desire. You will almost always leave feeling like you can change and that you want to change. The programs give you knowledge and goal-setting strategies for implementation, but these programs only address the intentional mind.

In a study on the “Take 5” program, 35 percent of people polled came away believing they should eat 5 fruits and vegetables a day. Looking at that result, it appears that the national program was effective at teaching people that it’s important to have 5 servings of fruits and vegetables every day. But the data changes when you ask what people are actually eating. Only 11 percent of people reported that they met this goal. The program changed people’s intentions, but it did not overrule habitual behavior.

According to Wood, there are three main principles to consider when effectively changing habitual behavior. First, you must derail existing habits and create a window of opportunity to act on new intentions. Someone who moves to a new city or changes jobs has the perfect scenario to disrupt old cues and create new habits. When the cues for existing habits are removed, it’s easier to form a new behavior. If you can’t alter your entire environment by switching cities— make small changes. For instance, if weight-loss or healthy eating is your goal, try moving unhealthy foods to a top shelf out of reach, or to the back of the freezer instead of in front.

The second principle is remembering that repetition is key. Studies have shown it can take anywhere from 15 days to 254 days to truly form a new habit. “There’s no easy formula for how long it takes,” Wood says. Lastly, there must be stable context cues available in order to trigger a new pattern. “It’s easier to maintain the behavior if it’s repeated in a specific context,” Wood emphasizes. Flossing after you brush your teeth allows the act of brushing to be the cue to remember to floss. Reversing the two behaviors is not as successful at creating a new flossing habit. Having an initial cue is a crucial component.

Breaking habits before they start

Our daily routines can become so ingrained that we perform them automatically, such as taking the same route to work every day. Some behaviors, such as smoking or biting your fingernails, become so habitual that we can’t stop even if we want to.

Although breaking habits can be hard, MIT neuroscientists have now shown that they can prevent them from taking root in the first place, in rats learning to run a maze to earn a reward. The researchers first demonstrated that activity in two distinct brain regions is necessary in order for habits to crystallize. Then, they were able to block habits from forming by interfering with activity in one of the brain regions — the infralimbic (IL) cortex, which is located in the prefrontal cortex.

The MIT researchers, led by Institute Professor Ann Graybiel, used a technique called optogenetics to block activity in the IL cortex. This allowed them to control cells of the IL cortex using light. When the cells were turned off during every maze training run, the rats still learned to run the maze correctly, but when the reward was made to taste bad, they stopped, showing that a habit had not formed. If it had, they would keep going back by habit.

“It’s usually so difficult to break a habit,” Graybiel says. “It’s also difficult to have a habit not form when you get a reward for what you’re doing. But with this manipulation, it’s absolutely easy. You just turn the light on, and bingo.”

Graybiel, a member of MIT’s McGovern Institute for Brain Research, is the senior author of a paper describing the findings in the June 27 issue of the journal Neuron. Kyle Smith, a former MIT postdoc who is now an assistant professor at Dartmouth College, is the paper’s lead author.

Patterns of habitual behavior

Previous studies of how habits are formed and controlled have implicated the IL cortex as well as the striatum, a part of the brain related to addiction and repetitive behavioral problems, as well as normal functions such as decision-making, planning and response to reward. It is believed that the motor patterns needed to execute a habitual behavior are stored in the striatum and its circuits.

Recent studies from Graybiel’s lab have shown that disrupting activity in the IL cortex can block the expression of habits that have already been learned and stored in the striatum. Last year, Smith and Graybiel found that the IL cortex appears to decide which of two previously learned habits will be expressed.

“We have evidence that these two areas are important for habits, but they’re not connected at all, and no one has much of an idea of what the cells are doing as a habit is formed, as the habit is lost, and as a new habit takes over,” Smith says.

To investigate that, Smith recorded activity in cells of the IL cortex as rats learned to run a maze. He found activity patterns very similar to those that appear in the striatum during habit formation. Several years ago, Graybiel found that a distinctive “task-bracketing” pattern develops when habits are formed. This means that the cells are very active when the animal begins its run through the maze, are quiet during the run, and then fire up again when the task is finished.

This kind of pattern “chunks” habits into a large unit that the brain can simply turn on when the habitual behavior is triggered, without having to think about each individual action that goes into the habitual behavior.

The researchers found that this pattern took longer to appear in the IL cortex than in the striatum, and it was also less permanent. Unlike the pattern in the striatum, which remains stored even when a habit is broken, the IL cortex pattern appears and disappears as habits are formed and broken. This was the clue that the IL cortex, not the striatum, was tracking the development of the habit.

Multiple layers of control

The researchers’ ability to optogenetically block the formation of new habits suggests that the IL cortex not only exerts real-time control over habits and compulsions, but is also needed for habits to form in the first place.

“The previous idea was that the habits were stored in the sensorimotor system and this cortical area was just selecting the habit to be expressed. Now we think it’s a more fundamental contribution to habits, that the IL cortex is more actively making this happen,” Smith says.

This arrangement offers multiple layers of control over habitual behavior, which could be advantageous in reining in automatic behavior, Graybiel says. It is also possible that the IL cortex is contributing specific pieces of the habitual behavior, in addition to exerting control over whether it occurs, according to the researchers. They are now trying to determine whether the IL cortex and the striatum are communicating with and influencing each other, or simply acting in parallel.

“A role for the IL cortex in the regulation of habit is not a new idea, but the details of the interaction between it and the striatum that emerge from this analysis are novel and interesting,” says Christopher Pittenger, an assistant professor of psychiatry and psychology at Yale University School of Medicine, who was not part of the research team. “Thinking in the long term, it raises the question of whether targeted manipulations of the IL cortex might be useful for the breaking habits — and exciting possibility with potential clinical ramifications.”

The study suggests a new way to look for abnormal activity that might cause disorders of repetitive behavior, Smith says. Now that the researchers have identified the neural signature of a normal habit, they can look for signs of habitual behavior that is learned too quickly or becomes too rigid. Finding such a signature could allow scientists to develop new ways to treat disorders of repetitive behavior by using deep brain stimulation, which uses electronic impulses delivered by a pacemaker to suppress abnormal brain activity.

Exploring the Brain’s Relationship to Habits

The basal ganglia, structures deep in the forebrain already known to control voluntary movements, also may play a critical role in how people form habits, both bad and good, and in influencing mood and feelings.

"This system is not just a motor system," says Ann Graybiel. "We think it also strongly affects the emotional part of the brain."

Graybiel, an investigator at the McGovern Institute of the Massachusetts Institute of Technology and professor in MIT’s department of brain and cognitive sciences, believes that a core function of the basal ganglia is to help humans develop habits that eventually become automatic, including habits of thought and emotion.

"Many everyday movements become habitual through repetition, but we also develop habits of thought and emotion," she says."If cognitive and emotional habits are also controlled by the basal ganglia, this may explain why damage to these structures can lead not only to movement disorders, but also to repetitive and intrusive thoughts, emotions and desires."           

Graybiel’s research focuses on the brain’s relationship to habits—how we make or break them—and the neurobiology of the habit system. She and her team have identified and traced neural loops that run from the outer layer of the brain—“the thinking cap,” as she calls it—to a region called the striatum, which is part of the basal ganglia, and back again. These loops, in fact, connect sensory signals to habitual behaviors.

Her work ultimately could have an impact not just on such classic movement disorders as Parkinson’s and Huntington’s diseases, but in other conditions where repetitive movements commonly occur, such as Tourette Syndrome, autism, or obsessive-compulsive disorder, the latter when sufferers experience unwanted and repeated thoughts, feelings, ideas, sensations or behaviors that make them feel driven to do something, for example, repeatedly washing their hands.

Moreover, the research could have an immediate value for trying to understand “what happens in the brain as addiction occurs, as bad habits form, not just good habits,” she says. “There are many psychiatric and neurologic conditions in which these same brain regions are disordered.

"These conditions may in part be influenced by the very system we are working on," Graybiel adds. "We are working with models of anxiety and depression, stress and some of these movement disorders."

It turns out that the emotional circuits of the brain have strong ties to the striatum, she says. Graybiel’s research suggests that activity in the striatum strongly affects the emotional decisions that people make: whether to accept a good outcome or a potentially bad one, for example, and that there are circuits favoring good outcomes, and, surprisingly, other circuits that favor bad ones.

"This work ties into new research suggesting that there are brain systems for ‘good’ and brain systems for ‘bad,’" she says. "What is intriguing is that we may have identified the circuits that decide between the two."

How the brain controls our habits

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 neuroscientists has found that a small region of the brain’s prefrontal cortex, 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 Brain Research 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 Proceedings of the National Academy of Sciences. 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.