Because I feel bad about neglecting the blog over the past month, here’s a special Tuesday edition of TRB, which may or may not become a regular feature. And, as it is a special edition, I’ll start with some food porn:
If I asked you to choose between eating the food from one of these pictures, how would you decide? Even if you are, like me, a fan of asparagus, you really can’t tell me it looks tastier than that Oreo cake. Of course, the asparagus and tomatoes do have something going for them. They’re clearly going to be better for you than the cake. If you’re particularly health conscious, you might be able to summon to willpower to forgo the deliciousness. But what’s actually going on in your brain when you’re making that decision? It might seem like a fairly trivial question, but it’s actually quite computationally interesting. Foods taste “good” to us because they offer some nutritional value that was necessary but scarce in our developmental history, like sugar, fat, or salt. We’ve inherited a motivational system that renders these treats extremely desirable and, in a world of surplus production, often leads us to harmful behavior. More recently, we’ve begun to understand the idea of the long-term health value of food and to make decisions about consumption using health as a consideration. Exactly how this happens, though, is an interesting question. We must pit abstract knowledge about health against instinctively motivational information about taste. It’s not exactly what philosophers are thinking about when they extol the virtues of man’s singular intelligence, but it likely involves the same neural processes.
This week in Science, Todd Hare, Colin Camerer, and Antonio Rangel published a paper offering some evidence about what’s going on in the brain when we choose between healthy and unhealthy foods. Using a set of images depicting 50 different foods, the researchers first asked subjects to report their personal judgments of the taste and healthiness of each item while in an fMRI scanner. From these ratings, the researchers selected a food for each subject that was neutral in terms of both health and taste for that individual. Then, over many trials, the subjects indicated their choice between each of the remaining foods and the reference item. (At the end of the experiment, they received their choice from a randomly selected trial).
The researchers found that the subjects fell into two well-defined groups. One group consistently chose the unhealthy option when they preferred it to the reference item, while the other group exercised more self-control and often chose the reference item over a comparator they had ranked high on taste but low on health. Brain imaging results primarily revealed the involvement of the ventro-medial prefrontal cortex (vmPFC), which is broadly implicated in the valuation of rewards. Interestingly, though, the response in vmPFC differed between the two groups. For those who effectively practiced self-control, vmPFC activity correlated with both their judgments of taste and healthfulness; in members of the other group, the health rating was not represented in the vmPFC response.
In other words, those subjects who exhibited self-control were able to use their assessment of a food’s healthiness to influence the subjective value signal that drove the decision process. Self-control behavior was also associated with increased activity in the dorsolateral prefrontal cortex (dlPFC), which is consistent with the theory that dlPFC is responsible for top-down executive control. It is not entirely clear how dlPFC interacts with vmPFC to pass a representation of healthiness into the valuation computation, but the two were functionally connected through a third region, the inferior frontal gyrus, which is involved in many studies of working memory.
We also don’t know how these patterns of brain activity relate to the subjective experience of study participants. It would be interesting to find out whether those in the self-control group were consciously thinking about the nutritional value of the healthy foods when they chose them, and, if this is even possible to measure, how that conscious thought correlated with activity in the cognitive control network. Still, the results of this study are practically helpful in a way neuroscience research often isn’t. If you want to make better decisions about what you eat, you have to relearn what to value.
Hare, T., Camerer, C., & Rangel, A. (2009). Self-Control in Decision-Making Involves Modulation of the vmPFC Valuation System Science, 324 (5927), 646-648 DOI: 10.1126/science.1168450
Oreo cake photograph by Flickr user ginnerobot; asparagus and tomato photograph by Flickr user Muffet. Both used under Creative Commons license.
