Cake or Death? Cake, please.
Today’s article comes to you from ars technica, where a friend of the blog found this article from Matt Ford on how we pick our food. Given that Sci is in the middle of reading “How We Decide” by Scienceblogs own Jonah Lehrer, she couldn’t pass this decision-making kind of article up. It was a conscious decision, I think. Or was it?
I don’t know about you, but everyone Sci knows appears to be trying to regulate their diet somewhat. Most of my friends think the word “die” is in the word “diet” for a reason. But we all still try to eat well, though we’re not going to be subsisting on grapefruit and wheatgrass juice any time soon. We’re all hearing the messages that we need to eat lean protein, get lots of fiber, and eat as many fruits and vegetables as we can afford.
The media nowadays is jam packed with advertisements saying we need to make healthy choices, right next to other advertisements letting us know about the many many offerings available at fast food restaurants for less than a dollar. With all this coming into your brain every day, it can be really hard to make the right decisions. Would a granola bar be good right now? Or should you have some fruit instead? Should you eat the chocolate cake or the ice cream?
And these decisions become even harder when it becomes a choice of fruit vs. cake (I don’t know about you guys, but the fruit would be languishing on Sci’s shelf for months). In these cases, your decision making has to have some layers to it. Rather than just “ooooh! Cake!”, you also need to think “eh, but I already HAD chocolate today, and I haven’t had more than one serving of fruit…and I should get more fiber because apparently everyone needs more fiber…”
Sorry, Banana. No contest. LOOK at the chocolate shavings on that thing…sigh…
So anyway. Our brains may want cake, and other parts of our brains want healthy. The two sides need to fight. But which areas of your brain are responsible? And how do they modulate each other? That’s what this group wanted to find out.
Hare et al. “Self-control in decision-making involves modulation of the vmPFC valuation system.” Science, 2009.
The recipe for a Science paper:
1) Take dieters
2) Put dieters in a scanner
3) Mix dieters vigorously with lots of different foods of varying tastiness
Ok, it’s a little more complicated than that. The researchers took a group of people, all of whom said they were on a diet. They then put them in a scanner, and showed them a whole bunch of foods, which they had to rate on two scales: health and taste. Looked like this:
The thing on the upper left is an apple. The other thing is a Butterfinger. So in this paradigm, most people would rank apples as high on health, and neutral to low on taste, while they would rate the Butterfinger as high on taste, but low on health. Of course, there were 50 options, for those who like neither apples nor Butterfingers.
Once the participants had rated all the items according to health and tastiness, they were shown one food (let’s say the apple), which they rated as neutral, both good for you and decent tasting. They then scanned the patients as they presented them with a set of decisions, and forced them to make a choice. Would you rather have the apple or the celery? How about the apple or the Butterfinger?
The authors suggested that dieters with higher levels of self-control (who might be more successful at maintaining a diet) would choose healthier foods in preference to non-healthy, tasty ones, and that dieters with lower levels of self-control would not. And sure enough, that’s what happened. They were able to divide the groups into high and lower levels of self-control, depending on the choices they made.
And then they scanned the brains of the dieters while they made those food decisions. They hypothesized that signals encoding “value” (yum) would be localized to the ventro-medial Prefrontal Cortex (the vmPFC). Activity in the vmPFC has been known to correlated with behavioral measures of value. You can see it here:
The activity in this area when the participants saw a food they thought was tasty was pretty equal across all patients. Mmm, that looks good. But what was the difference between those who went for the cake and those who restrained themselves? That was in the dorsolateral prefrontal cortex (DLPFC). Activity in this area increased when people restrained themselves and picked the healthy food, and was lower when people couldn’t stay away from the cake.
(The DLPFC, which showed more activity when participants exercised self-control)
Based on these results, the authors concluded that the basic value of an item was in the vmPFC, and that signals from this area were modulated by the DLPFC. So the more self-control you exerted, the more the DLPFC lit up, and the more you went and picked the apple because you knew it was good for you.
This study, which helps pinpoint where signals for self-control may originate, could be a big deal clinically. Not necessarily as a diet aid, but rather for problems where there’s a lack of self-control, as in addiction (where you have no self-control where the drug is concerned).
And it’s a pretty cool study, but Sci has some issues with it nonetheless. First of all, this is imaging. The most you can do (and the most the authors did, they didn’t say anything they couldn’t say) is draw a correlation between one area, another area, and a behavior. Correlation is not causation. We can’t say for certain that the DLPFC IS your self-control center. It could just be a relay area for measures of self-control coming from other places.
And I have a bit of an issue with the subjects in the study. There was no real control group. There were only dieters who had self-control, and those who didn’t. I’d want that paired up with a group of people who wasn’t dieting at all. I also want to know whether those who had more self-control were better at achieving their health goals than those with less self-control. And finally, I’d like to see a chart of people’s moods. If you make one bad decision and you KNOW you’re choosing a non-healthy option, does it make you give up? Are you more likely to just keep choosing the cake because you figure you’ve given in? Is higher activity in the DLPFC and a conscious healthy choice correlated with a positive feeling? Is it more likely to make a group show more self-control in the future? Studies which assess what the patient is experiencing as well as the choices they’re making could go further to address self-control issues in things like addiction.
The final issue is actually one with the data. the vmPFC lit up in the dieters when they assessed something of value. In dieters with higher self-control this area lit up when they perceived something they had ranked as HEALTHY. This means that healthy looked a lot better to them than it did to dieters with less self-control. And this makes you wonder whether the “self-control” dieters had more self-control after all, or whether they merely had grown to like carrot sticks. Not only that, an increase in vmPFC activity when self-control dieters saw something healthy could very well be MORE important in their choices than the modulating self-control activity from the DLPFC. I’m not at all sure how the authors might go about fixing this issue, but it’s definitely something to think about when you’re looking at people with “self-control”. Maybe, after you get hungry enough, even celery starts to look good.
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