Cookie or apple? Many of us would choose the cookie if we were by ourselves. But what about around others? If you have ever been at, say, a conference where you see many of your peers choosing an apple, you might choose one as well. New research suggests that this behavioral change also happens on the neurological level: Social norms shift brain activity related to how we value foods.
Harnessing these positive effects of conformity could be a boon for interventions aimed at healthy eating – something of vital importance, with obesity contributing to 2.8 million deaths worldwide annually. While past research has found a link between social norms and eating behavior, Erik Nook of Harvard University working with his then-adviser Jamil Zaki of Stanford University wanted to explore the psychological and neural mechanisms underlying the link.
They designed a study in which they asked hungry participants how much they liked a series of foods while their brains were scanned in an fMRI scanner. The participants saw food ratings provided by “200 of their peers,” but those ratings were manipulated so that the peers reported liking each food less than, as much as, or more than the participants themselves. The researchers then later asked participants to re-rate the foods while in the fMRI. They wanted to see how peer preferences affected participants’ follow-up ratings and neural responses to foods.
As published in the Journal of Cognitive Neuroscience, Nook and Zaki found brain activity showed both the extent to which participants were influenced by their peers, as well as a shift in how their brains valued the food based on social conformity. They found that activity in the nucelus accumbens predicted how much participants’ ratings conformed to their peers in the re-rating. And they found that activity in the ventromedial pFC tracked the popularity, rather than the healthfulness, of the foods – with increased activity occurring when peers liked a particular food more than the participants did.
Together, the findings suggest that “group norms can shift food preferences, supporting the use of norms-based interventions to promote healthy eating,” they wrote. Nook and Zaki spoke with CNS about these results and their significance, as well as the future of the work.
CNS: How did you personally become interested in studying this topic?
EN: I’ve long been interested in community-level interventions that can improve health and well-being. When Jamil and I discussed how social norms shape attitudes and behavior, I jumped at the opportunity to apply this to healthy eating!
JZ: Social conformity is a primary focus of my work, and I was interested in exploring whether norms could shift peoples’ responses to even basic preferences, for instance people’s desires for foods. I also saw the applied value of answering this question, for instance in using descriptive norms to encourage healthy behaviors.
CNS: What were you most excited or surprised to find in your results?
EN: I was excited to see that peer preferences were strong enough to impact preferences for both healthy and unhealthy foods. I think this is an important lesson for those who want to use norms to shift eating behaviors because these data imply that interventions should indicate that people regularly eat healthy foods and don’t eat unhealthy foods.
JZ: I was excited (though not surprised) to see that the magnitude of neural responses to learning that others agreed—as compared to disagreed—with them predicted people’s later conformity. This suggests that people who are most sensitive to the reward of “being on the same page” as others are also most likely to conform. This result gave us a marker of the extent to which people value the social experience of consensus, and it also supports a reward-based model of conformity that’s been on my mind for some years.
CNS: How does your work differ from, or fit in with, past work on food preferences and behavioral norms?
EN & JZ: We combined two literatures on (i) the neuroscience of social norms and (ii) how norms shift eating behaviors. Past studies have shown that social conformity involves regions implicated in reward learning and that people, in part, model their eating behaviors on the people around them. Here, we used a well-established fMRI paradigm of social influence to drill into the psychological and neural mechanisms that drive conformity for food preferences. This let us contribute to both literatures just by bringing them together.
CNS: What was the significance of the activity in the nucleus accumbens as it relates to social norms?
EN & JZ: The nucleus accumbens (NAcc) is consistently associated with reward learning across nonhuman and human neuroscientific studies. The NAcc interfaces with the prefrontal cortex and the midbrain to help individuals learn from past experience and shape future action. It does so by responding positively when an event’s outcome is better than expected – a positive prediction error – and responding negatively when an the outcome is worse than expected – a negative prediction error. These signals help the animal learn what actions they should repeat and which they should cease.
In our study, NAcc activity was greater when participants discovered that their rating was the same as their peers’ rating than when it was different. This suggests that our brains respond to group agreement and disagreement as if it were any other kind of reward (or absent of reward). In fact, people who had stronger NAcc responses to agreement were the same people who later changed their ratings to be more like their peers. This finding suggests that social conformity—even in regards to food preferences—occurs through a process of reward learning.
CNS: And what was the significance of your finding that the ventromedial prefrontal cortex related to food choice? Why was this important?
EN & JZ: The ventromedial prefrontal cortex (vMPFC) is thought to contribute to many psychological processes, but one that has received a lot of attention is its role in representing value. For example, activity in this region can predict which option someone will choose in forced-choice tasks. Here, we found that peer preferences shifted participants’ own food preferences, as well as vMPFC activity: vMPFC activity increased for foods that participants thought their peers liked more than them, compared to foods that they thought peers liked less than them. This suggests that social norms can shift neural representations of value.
We conducted some additional analyses to test whether changes in vMPFC activity were driven by changes in participants’ actual preferences for foods. We specifically wanted to verify that norm-driven changes in vMPFC activity and changes in self-reported ratings were related to each other, rather than just parallel. We found that the vMPFC responded strongest to foods that participants believed their peers liked and that they themselves said they liked more during re-rating. This result supports our interpretation that changes in vMPFC activity represents changes in participants’ actual preferences.
CNS: How can your findings inform behavioral interventions to curb obesity?
EN & JZ: We hope this research has clear “use-value” to public health. If people shift their food preferences towards group norms, interventions could promote healthier eating by informing people that their peers like healthy foods and dislike unhealthy foods. In fact, this is likely the process that produces local “food cultures” more globally. Although these interventions would need to be explicitly tested, these data provide initial evidence that they could work.
A second application of our work involves the NAcc result we describe above. It’s possible that our task could reveal who is most sensitive to group consensus and who is not invested in matching a group’s norm, just by examining NAcc responses to consensus and disagreement. Such an approach could potentially help target people who will be most receptive to social norms messaging.
CNS: What’s next for this work? What do you ultimately hope to accomplish?
EN: First, I’d like to scrutinize some of the assumptions connecting these results to interventions. For instance, we don’t know how long the preference shifts last or whether people will behave differently after learning their group’s norm. Second, I’d like to see whether descriptive norms could also be used to motivate other protective health behaviors.
JZ: My lab is currently investigating some of the assumptions Erik mentions, and we hope to see just how far social norms can go in encouraging healthy eating behaviors. We’re also examining other positive uses of social norms, such as building prosocial decision-making and empathy. In all, I hope to clarify for people that although conformity often gets a bad rap, it is actually “value neutral” and can encourage positive, as well as deleterious, behavior.
-Lisa M.P. Munoz
The paper, “Social Norms Shift Behavioral and Neural Responses to Foods” by Erik C. Nook and Jamil Zaki, was published online in the Journal of Cognitive Neuroscience on Feb. 11, 2015.
