Abstract
Casey, B. J., Somerville, L. H., Gotlib, I. H., Ayduk, O., Franklin, N. T., Askren, M. K., . . . Shoda, Y. (2011). Behavioral and neural correlates of delay of gratification 40 years later. Proceedings of the National Academy of Science, 108, 14998–15003.
Recent studies on children with language impairments indicate that they exhibit executive function deficits affecting attention, working memory, and self-regulation. Although intelligence is generally thought to play a key role in children’s early academic achievement, aspects of children’s executive function/self-regulation abilities are uniquely related to early academic success and account for greater variation in early academic progress than do measures of intelligence (Blair & Razza, 2007).
The Stanford marshmallow experiment conducted in 1972 was a study on deferred gratification, an aspect of self-regulation. The children, between 4 and 6 years of age, were led into a room where a treat of their choice (Oreo cookie, marshmallow, or pretzel stick) was placed on a table. The children could eat the marshmallow, the researchers said, but if they waited for 15 min without giving in to the temptation, they would be rewarded with a second marshmallow. Some covered their eyes with their hands or turned around so that they could not see the tray; others started kicking the desk, tugging on their pigtails, or stroking the marshmallow, whereas others simply ate the marshmallow as soon as the researchers left. The scientists analyzed how long each child resisted the temptation of eating the marshmallow and whether doing so had an effect on their future success. The purpose of the original study was to understand when the control of deferred gratification, the ability to wait to obtain something that one wants, develops in children. You can watch examples of the marshmallow experiment at http://www.youtube.com/watch?v=Yo4WF3cSd9Q
In more than 600 children who took part in the experiment, a minority ate the marshmallow immediately. Of those who attempted to delay, one third deferred gratification long enough to get the second marshmallow. Experiments on delay of gratification have demonstrated that part of the difference between children who delay and those who do not delay is due to the different cognitive strategies that individuals used during the task. Children who focus on “cool” cognitive features of the context (the shape of the marshmallow or envisioning the marshmallow as a cloud or cotton ball) are able to delay better than children who focus on “hot” or emotional features of the context (the sweet, delectable taste of the marshmallow). The same preschool child who yielded immediately to the temptation by representing the hot features of the reward (e.g., its yummy, sweet, chewy taste) could wait for long periods for the same tempting stimulus by focusing on its cool qualities (e.g., its shape). Although there appear to be naturally existing individual differences in the spontaneous use of such strategies, children can be taught strategies that can help them delay.
The first follow-up study, in 1988, showed that preschool children who delayed gratification were described more than 10 years later by their parents as adolescents who were significantly more competent. A second follow-up study, in 1990, showed that the ability to delay gratification also correlated with higher SAT scores. This 2011 study of the same participants indicated that the characteristic remains with the person for life. In addition, brain imaging showed key differences between the two groups—those who delayed gratification and those who did not—in two areas: the prefrontal cortex (more active in high delayers) and the ventral striatum, an area linked to addictions (more active in low delayers).
The 2011 study had two components. The researchers contacted 117 individuals from the original Stanford study. These participants were above average (high delay) or below average (low delay) in their original delay-of-gratification performance as well as in self-report measures of self-control administered in their 20s and 30s. More than half of these individuals agreed to participate in a longitudinal behavioral study (Experiment 1), and of these 59 participants, nearly half agreed to be part of a functional neuroimaging study (Experiment 2). The ability to resist temptation in favor of long-term goals is an essential component of individual, societal, and economic success. Even adults vary in their ability to resist temptations. Tempting situations can diminish control; what serves as a tempting situation that requires a capacity to control our impulses, however, changes as a function of age (e.g., from cookies to social acceptance). In this study, the researchers examined the extent to which individual differences in delay of gratification assessed when participants were in preschool and in their 20s and 30s predicted control over impulses and sensitivity to social cues at the behavioral and neural level when the participants were in their 40s. Delay of gratification depends importantly on cognitive control. Cognitive control involves the ability to suppress competing inappropriate thoughts or actions in favor of appropriate ones.
Study 1
Experiment 1 tested whether individuals who were less able to delay gratification as children and young adults (low delayers) would, as adults in their 40s, show less impulse control in suppression of a response to “hot” relative to “cool” cues. Metcalfe and Mischel (1999) proposed “cool” and “hot” systems to explain the dynamics of resisting temptation during the delay-of-gratification task. A “cool” system, involves cognitive control-related neural circuitry; a “hot” system involves desires and emotions that are under stimulus control and are associated with emotional brain regions. Recent brain imaging studies have provided evidence for dissociable brain systems related to immediate over long-term choice behavior consistent with the notion of interacting “hot” and “cool” systems. Top-down prefrontal regions have been shown to be involved in cognitive control during delay of rewards; limbic or emotional brain regions have been shown to be associated with more immediate choices.
The researchers for this current study developed two tasks to examine impulse control—one in the presence of neutral (“cool”) stimuli and one containing compelling (“hot”) stimuli. Because marshmallows and cookies are unlikely to be as rewarding to individuals now as adults as they were when they were young children, the researchers used the social cues of faces with emotional expressions (happy faces relative to neutral and fearful faces), shown to bias behavior similar to primary reinforcers. The experiment tested whether individuals who were less able to delay gratification as children and young adults (low delayers) would, as adults in their 40s, show less impulse control in suppression of a response to “hot” relative to “cool” cues.
Participants completed two versions of a go/nogo task. In a go/nogo task, participants press a button in response to one stimulus and do not press a button in response to a different stimulus. The “cool” version of the go/nogo task consisted of male and female stimuli with neutral expressions. Within a single run, both male and female stimuli were presented, one sex as a “go” stimulus to which participants were instructed to press a button, and the other sex as a “nogo” stimulus to which participants were instructed to withhold a button press. Participants were instructed to respond as quickly and accurately as possible. During the task, a face appeared for 500 ms, followed by a 1-s interstimulus interval. A total of 160 trials were presented per run in pseudorandomized order (120 go, 40 nogo). The “hot” version of the go/nogo task was identical to the “cool” version, except that for this task, fearful and happy facial expressions served as stimuli. Both expressions were used as targets (go) and nontargets (nogo). Stimuli consisted of happy, fearful, and neutral faces of unique identities.
Results of Study 1
Individuals who as preschoolers were easily tempted by the marshmallow or cookie had more difficulty suppressing inappropriate actions on the “hot” go/nogo tasks (that used emotional expressions) than did those who as preschoolers were able to resist eating the marshmallow or cookie, particularly on more difficult trials. (There were no differences on the go/nogo tasks that used neutral expressions.) Difficulty was manipulated by increasing the number of “go” trials preceding a “nogo” trial, thus making the “go” response more salient and automated. Differences between the high- and low-temptation-focus groups increased as the number of preceding “go” trials increased, with the high-temptation-focus group having more difficulty, reflected in slower response times and difficulty suppressing inappropriate responses. These findings suggest that performance in preschool delay of gratification may predict the capacity, in adulthood, to control thoughts and actions, as reflected in performance on cognitive control tasks, and that the ability to control one’s thoughts and actions can vary by the potency of interfering information. Likewise, tempting or social contexts can diminish self-control.
Study 2
In Experiment 2, the researchers used functional magnetic resonance imaging (fMRI) to examine neural correlates of delay of gratification. Participants completed hot go/nogo tasks as in Experiment 1 while having an fMRI scan. They hypothesized that participants with consistently low levels of self-control from young childhood to early adulthood (low delayers), compared with their consistently high-control counterparts, would be characterized by diminished activity in the right prefrontal cortex, implicated in response inhibition, and by amplified activity in the ventral striatum, implicated in the processing of positive or rewarding cues.
Key Findings
The results from both experiments together suggest three key findings.
Individuals who, as a group, had more difficulty delaying gratification at 4 years of age continued to show reduced self-control abilities. Resistance to temptation as measured originally by the delay-of-gratification task, and in the present study by a “hot” version of an impulse control task (using positive social cues of a smile), is a relatively stable individual difference characteristic.
Consistent with delay of gratification experiments on the value of “cooling” the hot features of temptations, behavioral correlates of delay ability involve not cognitive control in general, but in particular in response to positive compelling cues.
Resisting temptation is supported by ventral frontostriatal circuitry, with the inferior frontal gyrus showing lesser recruitment in low delayers and the ventral striatum showing exaggerated recruitment in low delayers when resisting alluring cues. These findings suggest that sensitivity to positive social cues influences an individual’s ability to suppress thoughts and actions and thus can undermine self-regulation.
Resisting temptation requires impulse control. The go/nogo task is considered a reliable measure of impulsivity. In the present study, the “cool” version of the go/nogo task did not differentiate the low- and high-delay groups. Only in the presence of positive social (“hot”) cues did the go/nogo task reveal differences between the two delay groups. The behavioral correlates of delay ability are a function not only of impulse control but also of the salience of the stimulus one has to resist. Two neurocognitive systems that rely on distinct neural systems have been proposed to enable self-control. The “cool” system involves cortical control regions, including the prefrontal cortex, whereas the “hot” system involves deep brain structures that are implicated in the processing of desires and rewards.
Sensitivity to environmental cues influences an individual’s ability to suppress thoughts and actions. Resisting temptation in favor of long-term goals is important for individual, societal, and economic functioning. The findings of this study provide a neurobiological basis for differences in persons’ ability to control their behavior. Together, the behavioral and imaging findings provide evidence that the ability to delay gratification assessed early in life predicts how well individuals can regulate behavior years later, particularly when they are required to suppress thoughts and actions toward alluring social cues.
Comments
The marshmallow study and its follow-up studies indicate that there is a neurobiological basis for self-regulation as manifested by controlling impulses to delay gratification and that this impulse control remains fairly stable over one’s lifetime. Do these results imply, then, that a person’s impulse control and ability to delay gratification cannot be modified? There is evidence to indicate that even behaviors that are neurologically based can be modified. Doige (2007), in his book The Brain Changes Itself, reported many ways in which neurological functioning changes and can be changed.
Promoting opportunities for children to participate in imaginative play can facilitate development of impulse control. Children who engage in more frequent and higher levels of pretend play exhibit greater self-regulation. Berk, Mann, and Ogan (2006) suggested that pretend play promotes self-regulation in two ways:
Pretend play helps children separate mental representations from the objects and events for which they stand. When pretending, children practice acting independently of what they see. In play, children begin to use symbols as tools for overcoming impulse and managing their own behavior. Pretend play strengthens children’s internal capacity to be socially responsible.
Play is rule-based—Children devise and follow social rules in pretend play. This strengthens their sensitivity to external pressures to act in socially desirable ways.
Language has the potential to facilitate self-regulation/impulse control (Luria, 1961; Vygotsky, 1962). For example, Gawrilow, Gollwitzer, and Oettingen (2011) reported that teaching children to use “if–then” statements rather than goal statements significantly affected their ability to control their behavior in learning situations. In this present study, a goal statement might be, “I’ll push the button when I’m supposed to,” whereas a more specific if–then statement would be, “If I see the fearful face, then I’ll push the button,” “If I see the smiling face, then I won’t push the button.”