Early Childhood

Study Reveals Brain Biology Behind Self-Control

By Sarah D. Sparks — September 20, 2011 7 min read
Eleven-year-olds Alaney Ocasio, left, and Nirisi Lopez give in to their impulse to eat marshmallows after a mini-lesson on self-control at the KIPP Academy Middle School in New York City.
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A new neuroscience twist on a classic psychology study offers some clues to what makes one student able to buckle down for hours of homework before a test while his classmates party.

The study, published in this month’s edition of Proceedings of the National Academy of Science, suggests environmental cues may “hijack” the brain’s mechanisms of self-control in some people and some circumstances.

The findings add to a growing body of research suggesting that a student’s ability to delay gratification can be as important to academic success as his or her intelligence—and that educators may soon know how to teach it.

More than 40 years ago, Stanford University researchers led by Walter Mischel conducted a now-famous study in self-control: They asked 4-year-olds at Stanford’s Bing Nursery School to hold off eating one sweet in exchange for the promise of two sweets 15 minutes later. Fewer than one in three children passed the so-called “marshmallow test.”

In the years that followed, numerous follow-up and variation studies have found that the preschoolers who managed to delay gratification were also more likely later on to do well in school, avoid substance abuse, maintain a healthy weight, and even perform better on the SAT than peers who couldn’t resist temptation.

The studies by Mr. Mischel, who is now a psychology professor at Columbia University, and a cadre of other researchers have helped change the way scholars and educators think about why students succeed academically. In a separate self-control study, Angela L. Duckworth, an assistant psychology professor at the University of Pennsylvania, even found that self-control was a better predictor of a student’s academic performance than an IQ test.

Yet the brain has remained a missing piece of the puzzle, according to B.J. Casey, the director of the Sackler Institute for Developmental Psychobiology at the Weill Cornell Medical College in New York City. The new study is the first to compare brain differences among those original Stanford preschoolers.

“What we wanted to do is try to understand how the brain is related to this behavior,” said Ms. Casey, who led the new study. Brain imaging, she said, “is helping us to disentangle the impulse control from sensitivity to rewards and social cues.”

Marshmallow Restraint

In a classic social science experiment, researchers tested young children’s self-control by leaving them alone with a marshmallow and a choice: They could either eat the marshmallow right away or wait and get even more sweets. A New York City teacher explains how he draws on that experiment to teach his middle school students to exercise a little self-control.

Control in the Brain

Of the 562 Bing Nursery School pupils who took part in the original Stanford study in the late 1960s and early 1970s, 155 participated in a follow-up in 1993 and 135 in another in 2003. Ms. Casey’s team focused on 60 who consistently showed a high ability to delay gratification and another 57 with consistently low ability to delay.

Marshmallows and pretzels may not hold the same allure for those in their 40s as they do for preschoolers, but the enjoyment of a positive social cue, such as a smiling face, has proved to be just as powerful emotionally for adult study participants.

Ms. Casey and her team tested the participants’ ability to push a button—or refrain from pushing it—in response to seeing images of happy, fearful, or neutral faces. After conducting the first round of tests, the team asked 27 of the participants to redo the trials while undergoing functional magnetic resonance imaging, or fMRI, which uses blood flow to measure activity in the brain.

Researchers found that the brain seems to bring two different areas to bear when a decision is made.

In an objective, unemotional question—Is it better to have one item now or two items in 15 minutes?—the brain triggers the prefrontal cortex, which helps us make rational decisions. Other decisions are more urgent and more dependent on context—Should I run from the wolf? Should I eat this food?—and here, environmental and social cues can activate a deeper, more primitive part of the brain, the ventral striatum, which is associated with processing desires and rewards.

As it turns out, Ms. Casey said, people who have difficulty delaying gratification also tend to be “very, very sensitive to environmental cues.” All of the adults in the study were able to respond correctly in neutral situations. Differences arose between the adults who could delay gratification as children and those who couldn’t during tests in which they were asked to counter a strong environmental cue.

The biggest difference between the two groups occurred when participants had been asked to press the button several times in a row for a happy face, which researchers consider a strong positive social cue, and then suddenly were asked not to respond to happy faces. Those who had demonstrated poor delay of gratification as children were much more likely to push the button in response to a happy face even when they were not supposed to do so.

Environmental Cues

“Sensitivity to environmental cues influences an individual’s ability to suppress thoughts and actions, such that control systems may be ‘hijacked’ by a primitive limbic system, rendering control systems unable to appropriately modulate behavior,” the researchers found.

Experts said this finding might help explain the dip in self-control that parents and teachers often report in teenagers.

“We’ve shown developmentally that [impulse control and environmental sensitivity] are separate; impulse control gets better and better as you get older,” Ms. Casey said. “Children are more impulsive than adolescents, but right around puberty there’s a much greater sensitivity to social cues and environment, and adolescents are more sensitive to social cues than either children or adults.”

Teasing out how impulse control and environmental sensitivity work together has “strong implications” for ways of intervening with children and adults who have trouble with self-control, she said.

For example, prior studies have found that young children can hold off eating a marshmallow if they are told to focus on “cool” cues like its shape or color, rather than emotionally “hot” cues like taste.

And Adele Diamond, a professor of developmental cognitive neuroscience at the University of British Columbia, in Vancouver, found that preschoolers can learn to wait to take turns more effectively when they are given concrete social cues, such as holding a picture of a mouth when speaking and a picture of an ear when listening.

Mr. Mischel and Ms. Duckworth have been studying whether it’s possible to teach students how to delay gratification and improve self-control through school-based interventions.

In a 2010 study, Ms. Duckworth found that high school students who visualized both their academic goal for an upcoming high-stakes exam and potential pitfalls in meeting that goal answered 60 percent more questions on a practice exam than peers who had not done the exercise.

Ms. Duckworth is currently working on two separate evaluations of self-control instruction in New York City and Philadelphia.

In New York, four charter middle schools operated by the Knowledge Is Power Program, or KIPP, a San Francisco-based education-management organization, started their pilot last year, adding character grades to students’ academic report cards twice a year. The report cards have seven indicators—zest, grit, self-control, hope/optimism, curiosity, gratitude, and social intelligence—and include a two-part measure of a student’s self-control that takes into account both academic and social behavior. This year, the schools are testing class lessons on strategies to improve self-control.

In the Field

Last week, Mitch Brenner, the assistant principal at the KIPP Academy Middle School in New York, used one such lesson to explain the original “marshmallow experiment” to a class of 6th graders. He asked them to talk about how they would have decided whether or not to eat the sweet, and how self-control relates to the school’s academic requirements.

“We are asking kids to make sacrifices in the course of their careers here,” said Mr. Brenner, who is developing the lessons as part of the pilot study. “You are putting in long hours, you are doing homework while you would rather be playing video games or watching TV, and that can have benefits down the road, but it can be tough, particularly for a kid. We want to give them exposure to that idea, motivate them and help get them thinking.”

The KIPP school also created a “character-rific” honor board to leverage adolescents’ social sensitivity to improve rather than impede their self-control. Students nominate classmates or teachers as having good character based on self-control and other qualities.

“I can tell kids all day what grit looks like, what self-control looks like, but when the kids give the examples, that’s where the real power comes from,” Mr. Brenner said. “Some kids may struggle more academically, but when they get shouted out as being a good person, that feels great.”

Back in Mr. Brenner’s class on self-control, students got their own marshmallows and debated the pros and cons of immediate versus delayed gratification. At the end of the class, Mr. Brenner let the students eat their marshmallows—though one boy opted to save his for later.

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A version of this article appeared in the September 21, 2011 edition of Education Week as Study Reveals Brain Biology of Self-Control


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