Credit: >a href="">Kate Ter Haar (Flickr).Credit: >a href="">Kate Ter Haar (Flickr).

What A Marshmallow Can Say About Your Brain

by • August 14, 2017 • Deirdre Sackett, NeuroscienceComments (0)473

By Deirdre Sackett

In the 1970s, researchers at Stanford University performed a simple experiment. They offered children the chance to eat a single marshmallow right now, or wait 15 minutes to receive two marshmallows. Out of 600 children in the study, only about ⅓ were able to wait long enough for two treats. Most attempted to wait, but couldn’t make it through the whole 15 minutes. A minority of kids ate the marshmallow immediately.


Feeding marshmallows to children in the name of science may seem like a waste of federal funds. But it turns out that the ability to wait for a treat can actually predict a lot about someone’s personality and life trajectory.


Since the 70s, many scientific groups have repeated the “marshmallow test” (some of which have been hilariously documented). In some iterations, researchers recorded whether each child chose an immediate versus delayed treat, and then tracked the children’s characteristics as they grew up. Amazingly, the children’s choices predicted some important attributes later on in life. Generally, the more patient children who waited for the bigger reward would go on to score higher on the SAT, have a lower body mass index (BMI), and were more socially and cognitively competent compared to the kids who couldn’t wait and immediately ate one treat.


The “marshmallow test” measures a cognitive ability called delay discounting. The concept is that a big reward becomes less attractive (or “discounted”) the longer you need to wait for it. As such, delay discounting is a measure of impulsivity – how long are you willing to wait for something really good, before choosing a quicker, but less ideal, option?


While it’s okay to occasionally have spur-of-the-moment choices, poor delay discounting (increased impulsivity) is often a symptom of problematic gambling, ADHD, bipolar disorder, and other mental health issues. In particular, drug addiction is also accompanied by increased impulsive choices. For instance, drug users will choose immediate rewards (such as drugs of abuse) over delayed, long-term rewards (i.e., family life, socializing, or jobs). Drug users are poor at delay discounting and choose immediate options faster than non-drug users. This isn’t just a human flaw; exposing rats to cocaine also increases their impulsivity during delay discounting tasks.


Interestingly, aspects of the “marshmallow test” hint at this impulsivity-drug addiction link. In 2011, researchers did a follow-up study with the (now adult) children from the original 1970’s Stanford experiment. The scientists imaged the subjects’ brains while making them do a delayed gratification task in which they had to wait for a reward. They found that patient versus impulsive individuals had very different activity in two specific brain regions involved in drug addiction.


Firstly, the study found that impulsive individuals had greater activity in the ventral striatum, a brain region heavily linked to drug addiction and impulsivity. The greater activity in this region may imply that impulsive individuals process information about rewards differently than patient individuals. That is, the way their brain is wired may cause them to want their rewards right now.


Secondly, the impulsive individuals had less activity in the prefrontal cortex, which is responsible for “putting on the brakes” for impulsive actions. This finding suggests that impulsive individuals may not have that neural “supervisor” that can stop themselves from acting on their impulses. Drug addicts show similarly reduced prefrontal activity. So in addition to doing worse on standardized tests, having higher BMIs, or being less socially competent, the marshmallow test predicts that impulsive individuals may have brain activity similar to those of drug users.


While it seems like a silly experiment, the marshmallow test is a great starting point to help increase our understanding of impulsivity. Using this information, researchers can start to develop treatments for impulsive behavior that negatively affects people’s lives. Specifically, treating impulsivity in drug addicts could help as part of the rehabilitation process. So think about that the next time you reach for that sweet treat!


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