IRA FLATOW, HOST:
Ever wonder why you worked so hard to avoid the lasagna at dinner only to give in to your craving for not one but two helpings of cake for dessert? Well, new research may hold some answers to this vexing question. A new study in the Journal of Consumer Psychology confirms what we've been - what we've known for some time, and that is each of us has an internal reservoir of self-control. We have a reservoir of self-control that it depletes. Every time we resist a temptation, we use a little bit of it up.
But for the first time, researchers have taken pictures of the brain to show what was happening when a person exerts and then loses self-control. Dr. William Hedgcock was a co-author of the study. He is a neuroscientist and assistant professor of marketing at the University of Iowa. He joins us from Denver. Welcome to SCIENCE FRIDAY.
DR. WILLIAM HEDGCOCK: Oh, thanks for having me.
FLATOW: Well, first, let me back up a bit because I think it would be surprising to most people to learn that we actually have a reservoir of self-control.
HEDGCOCK: Sure. So this is a theory called regulatory resource depletion. And like you said, when people exert self-control, what we see is people have a hard time exerting self-control later, so this idea of one resource may be, you know, not intuitive. But I think most of us have had this sort of experience where you exert self-control at one point and then end up succumbing to temptation later.
FLATOW: Mm-hmm. And where is that center of self-control?
HEDGCOCK: Well, what we're finding is that the center seems to be the dorsolateral prefrontal cortex, so it's an area that's sort of near the temple and underneath the temple of your head.
FLATOW: Hmm. And how do we know that that's where it is?
HEDGCOCK: Well, so we ran an fMRI study where we had subjects come into the scanner. They first exerted self-control, and we saw them having activation in areas like the dorsolateral prefrontal cortex and the anterior cingulate cortex. And this is what, you know, we would have expected. Then we had them exert self-control later on a subsequent task, and we saw less activity in this dorsolateral prefrontal cortex area.
FLATOW: So it had been depleted in - some of their self control was gone.
HEDGCOCK: Yeah. So we saw behaviorally that they had less self-control, and that seemed to be correlated with the fact they had less activity in that area.
FLATOW: Now, is the reservoir a reservoir of chemicals? Is it a reservoir of neurons? What exactly is the reservoir?
HEDGCOCK: So we don't really know that yet. We do know that there's less activity in that area. It seems unlikely that it's a neurotransmitter, for instance, but we would need some follow-up studies to find out exactly why is it less active there.
FLATOW: Mm-hmm. And what kind of test do you do when you test people for their self-control? Do you put pie in front of them and say, you can only have one bite or what?
HEDGCOCK: Well, that certainly - some people do that. So we'll put people in front of brownies or something and then see later, would they like to choose brownies versus a healthy snack or - also, we test them on things like, will they perform well on a cognitive task. But in the scanner, we couldn't do that. It's difficult to, you know, put a pie next to a person in the scanner.
HEDGCOCK: So what we did was something a little bit more sterile than that. We had them look at a fixation point on a screen, and we flash words underneath the fixation. And the words would move around and - but they're very close to the fixation. We told subjects to ignore them and definitely not read them, but this was difficult or, for the most part, impossible for subjects to do. So it required self-control on their part to not read the words.
FLATOW: Don't think of pink elephants.
HEDGCOCK: Yeah. Well, so that's another version of - or another way to manipulate self-control. You could have them not think about elephants, which is difficult to do once we mention it to you.
FLATOW: Right. 1-800-989-8255. Talking with Dr. William Hedgcock about exerting self-control. And so can you actually tell at the moment by looking at the scan when, uh-oh, they've lost their self-control?
HEDGCOCK: Well, what we saw was sort of a gradual depletion over time. We didn't see a particular timeframe. And by the way, our subjects sometimes were able to exert self-control later. It's not like they completely lost it. They were just less able. They just occasionally would succumb to temptation more frequently than when they were not depleted.
FLATOW: Mm-hmm. Let's see if we can get a phone call in here from Bill in Loma Linda, California. Hi, Bill.
BILL: Hi there. Thank you for taking my call. I love your show.
FLATOW: Thank you.
BILL: I'm really interested in this subject, neuroscience and self-control. And you guys - it's fascinating. I was wondering just - if your guest speaker had any idea or any speculation on how we can maybe improve self-control or modulate the self-control, you know, maybe modeling it in an animal study and then improving self-control.
FLATOW: Yeah, because you got to - you're going to bet I'm sure, and let me ask Dr. Hedgcock about this, that the pharmaceutical companies would be very interested in a pill, right?
HEDGCOCK: Well, I think the pharmaceutical, you know, companies and also, you know, just people or policy makers in general. You know, we just ran a quick behavioral experiment to see what would happen and it seems pretty simple, but what we had people do is think about ways they would actually execute control. So we went to a gymnasium. We had people coming out who had this sort of fitness goal or eating healthy goal, and we would just have them think about ways that they would execute that. So come to the gym three times a week or, you know, eat healthy and not - versus unhealthy foods. And that would slightly improve it.
We don't think that - we don't think that it replenished the resource, so to speak, but it was sort of a crutch. It would just make it easier to exert control. But, as you mentioned, this idea of pharmacological interventions, it, you know, it's too early to tell exactly what would be useful. But these brain images provide us at least with some direction on where we should look.
FLATOW: Mm-hmm. Do you know how it's replenished? Did you image participants' brains after a period of time to find out?
HEDGCOCK: So no, we didn't do that. It would seem to take a while. Right now, all we know that will help you is to take a break. So just do something that doesn't require self-control. You know, if you take a nap or if you are somewhere where its easy to exert self-control so that you don't sort of tire it out, it seems that people are able to replenish it that way.
FLATOW: I guess it's sort of like the - what people tell you if, you know, take yourself out of that situation that's giving you a loss of self-control.
HEDGCOCK: Yeah, that's correct. And not only will it help you right there at that situation, but it might help you later when you're trying to exert self-control in a later time when it's harder to avoid temptation.
FLATOW: So have you found that you can practice self-control?
HEDGCOCK: So I have not personally run that study, but we do know other researchers have looked at that and found that if you practice self-control, you're able, actually, to strengthen this or improve your resource so that you'll have a better ability to not wear out over time.
FLATOW: It's like the muscle theory, right? If you use your muscle over and over again, you strengthen it.
HEDGCOCK: Yeah. At least in these two ways, this sort of muscle analogy seems to fit with how your regulatory resources work.
FLATOW: Let's go to Austin in Sand Point, Alaska. Hi, Austin.
FLATOW: Hey there.
AUSTIN: ...thanks for taking my call.
FLATOW: You're welcome. Go ahead.
AUSTIN: Hey. I had - I study theology as a pastor, and I was curious: did you notice anything like correlations between people with the religious convictions and increased self-control or decreased self-control or anything like that?
HEDGCOCK: You know, I'm sorry to say, we did not end up looking at that - that's an interesting question - things like, you know, religiosity or personality traits or gender. Honestly, the things that we've looked at, when we have looked at those, they don't tend to be a very big predictor. But I haven't specifically looked at religion.
FLATOW: All right. Thanks for calling, Austin. Can you - if you look at an image of the brain - a brain scan of somebody, can you tell from looking at the scan how much self-control they have or have - how much reservoir they have left?
HEDGCOCK: No, we can't do that. I'm sure people would be interested. You know, just because an area of the brain is bigger, it doesn't necessarily mean that it would be, you know, more, you know, stronger, let's say. So, a large DLPFC or small, it doesn't tell us that people are better able at exerting self-control. I suppose the only media exception to that would be if someone has brain damage to an area, so particularly taking out that area, then you might be able to predict that they'd be very bad at self-control.
FLATOW: We have a tweet from Kaye McKenzie(ph), who says: I wonder if this could help alcoholics, and the like, to resist temptation?
HEDGCOCK: So things like alcoholism are a little bit different. But certainly, with the idea of when they are trying to resist temptation that this could help them out.
FLATOW: This is SCIENCE FRIDAY from NPR. I'm Ira Flatow talking with Dr. William Hedgcock, author - co-author of a study about self-control. Let's see if we can get to another phone call or two. But before I get to that, and the second part of your study, you looked at ways to intervene and make people aware of the consequences of the choices that they were making. Were they less likely to lose self-control with this kind of intervention if they knew the consequences?
HEDGCOCK: So if we had them think about consequences, it did not seem to help them too much. On the other hand, if we had them think about ways that they would actually execute control, it did help them. And in particular, we had them choosing from tempting versus, you know, healthy snacks, and we saw that their snack behavior would change if they thought about ways that they could make better decisions.
FLATOW: Mm-hmm. Did you try to distract them at all and see if that would bring self-control, a little bit, back?
HEDGCOCK: No. So we did not look at distracting them later. Often, we would use a distraction sort of thing to diminish their ability to their self-control.
FLATOW: Mm-hmm. Go the phones, to Jamie(ph) in Cleveland. Hi, Jamie.
FLATOW: Hi there.
JAMIE: Thank you for taking my call.
FLATOW: You're welcome.
JAMIE: I remember hearing an article on NPR, once, that - about a study to a - with dieters. And they had people think about very specifically eating M&M's, and the crunching and the taste and swallowing. And then afterwards, the control group that was not told to think about eating M&M's had way too bit - ate way more M&M's than the people who thought about it. And I was just wondering what you think the self-control, and if you can trigger a brain into having more self-control by thinking - by making it think we've already given it.
HEDGCOCK: Actually, I believe - if I'm thinking of the same study you're talking about, I believe what they're doing is satiating people. So basically, if you're imagining eating, you know, M&M after M&M, eventually, even though you're just thinking about it, it can make you start to think that you're getting tired of eating them. So this sort of, you know, perceptual satiation is happening. So, you know, if you had them, for instance, eat just two or three, it might actually make them more - make it harder to resist temptation. But after eating 30 or 40, they start to think, well, I don't find these very appetizing anymore. I'd prefer not to eat them. So it's definitely possible to sort of mentally, to convince yourself to eat more or less that way.
FLATOW: Mm-hmm. Let me see if we get more question from Molly in Washington, D.C. Hi, Molly.
MOLLY: Hi, guys. Thanks for taking my call.
MOLLY: So I read a book, last year, called, "Willpower," exactly on this topic, and its central premise was that you can improve that depleted resource of willpower/self-control, as we're calling it in this study here, through glucose. And I was wondering if the author could talk about that. They proved, in my mind, pretty positively that a regular intake of glucose, not necessarily super sugary substance, but that base, I guess, willpower generator, could really improve your discipline.
FLATOW: All right. Let's get an answer. Thanks for the question.
HEDGCOCK: So I believe that that book and the study was someone named Roy, excuse me, Roy Baumeister did that research. And they have found that if you have people drink sugary substance, that can end up increasing people's self-control. Our study does not directly address that. I guess, our results are consistent with that, and that we less activation in the brain and that could hypothetically be from lack of glucose. But at this point, all we can say is that there's just less activity in that part, and we don't know why.
FLATOW: As an assistant professor of marketing, do you think that marketing people would love them to convince you how to lose self-control and go on and buy their product?
HEDGCOCK: Yeah, so it's certainly possible. That's one way that marketers could use this information. Actually, there's just as many marketers who would like to improve your self-control, so you could think about, you know, fitness clubs or diet companies, or, you know, particularly finance companies or retirement savings. You know, they could only make money if you actually do exert self-control, and we hoped they'd find it useful to figure out and how to improve that.
FLATOW: Dr. Hedgcock, thank you very much for taking time to be with us.
HEDGCOCK: Oh, thanks for having me.
FLATOW: Have a good weekend. William Hedgcock, neuroscientist and assistant professor of marketing at the University of Iowa, also co-author of a study in the Journal of Consumer Psychology.
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