Does stress trigger your chocolate habit?

There are many behavioral tasks out there which use monkeys. But a lot of people lately are asking the question: why use monkeys when you can use humans? Of course, for some of these tasks, conditions have to exist that we would be unable to obtain in humans, but there are some simple behavioral tasks which a rat, a monkey, and a human can do equally well. And Sci must imagine that tasks like this involve some amusement factor on the part of the experimenter. After all, if something looks cute when a rat is doing it, it often makes a human look profoundly ridiculous.
And this paper is interesting for other reasons. There are a lot of questions as to how well humans REALLY operate in times of stress. Perhaps some of us may think that stress facilitates our abilities. And in some people, that might be the case. But it also appears that stress brings out other behaviors in humans that may not be as positive as you think.
ResearchBlogging.org Schwabe and Wolf. “Stress promts habit behavior in humans.” The Journal of Neuroscience, 2009.
Today’s study brought to you by Nestle Quik
NestleQuickInstantChocolateDrinkMix.gif
And a lot of oranges
Oranges_and_juice.jpg
You’ll see why.


It’s been known for some time that there are two major types of learning systems, “cognitive”, and “habit”. The cognitive system relies on the prefrontal cortex, while the habit system relies on the dorsal striatum, in an area of the brain known as the caudate. While figuring something out and learning something will involve the prefrontal cortex, once that sequence has become habit, or the reward it involves has ceased to have value, the caudate becomes involved. In the caudate, you do it just…because. Because you ALWAYS do.
So the question these experimenters wanted to answer was whether or not stress affects how people react to cognitive versus habit related choices. To do this experiment you will need:
A human
A computer
Ice water and a video camera
Some oranges
A ton of chocolate pudding and chocolate milk
Peppermint tea
No, really.
These experimenters took a bunch (is 80 a bunch? A bunch to me seems more like 12. I guess it’s “a lot”) of hungry college students, who rated orange juice and chocolate as being equally valuable (kind of wacky, but who is Sci to say). They put half of the students under a stressful condition, and the other half under a non-stressful condition. You might think a stressful condition to a college student might be, say, a hard math test, or sitting in a room while a group of people whisper barely heard things about you from the other side of the door. While those two things are indeed stressful, there’s something a lot simpler (and a lot less psychologically damanging) that can be done instead. To stress out a human, have them hold their hand in ice water while someone else videotapes it.
I was describing this experiment to Mr. SiT, and he pointed out that he didn’t think he’d be very stressed out by that. But he would be surprised. Holding your hand still in ice water for a period of three minutes is in fact pretty physically stressful, it’s very uncomfortable, and many people would withdraw their hand pretty quickly. But then, videotape them. With someone watching you, you’re more likely to hold your hand in longer, exposing yourself to more of a stressful condition. You wanna be tough, right? And while ice water might not seem too stressful, your body doesn’t agree. Your heart rate and blood pressure will go up, and you will start producing increased levels of the stress hormone cortisol.
Once the students had been adequately stressed, they brought them into a room with a computer. They then had to stick a little straw in their mouths, pick up the mouse, and figure out the correct response to three conditioned. There were two high probability conditions, one neutral condition, and a low probability condition. If you pressed the dark circle, half the time you would get a shot of chocolate milk through the straw. If you pressed the little weird shaped blob, half the time you would get a shot of orange juice through the straw. However, IF there was ALSO a triangle or a spiral along with the circle or blob, there was a 20% chance of getting peppermint tea through the straw (coming right before orange juice, I could see this being nasty, but apparently nobody minded). Finally, there was the neutral condition, where if there was a bar, you would get water, and if there was a hexagon, you would also get water. The whole thing looked kind of like this:
zns9990965580001.gif
They had about 225 trials to figure all of this out. After that, they took the hungry college students into a room, and allowed them to eat either oranges, or chocolate pudding, until they didn’t care. I imagine, given the high metabolism of some college students she has seen, that this could indeed be a LOT of oranges and chocolate pudding. Anyway, you get lots of pudding or oranges, as much as you can eat, and you’re supposed to eat until you don’t want any anymore. This is supposed to make the orange or the pudding a HABIT. You get it all the time, it doesn’t hold much value for you anymore, it’s just something you were just kind of eating.
And then they took the people back into the room (remember, half of them were stressed with ice water and videotaping, the other half were not), and ran them on the test again. This time, no matter what buttons they tried to press, they got peppermint tea. This is called extinction, and in the case of things like drugs or sugar pellets, will leave a poor rat banging on the lever in frustration until he gives up. In the case of the students with pudding and orange juice, they started banging on the keys, clicking random things.
Or WERE they clicking random things? Indeed, they were not. In the case of the non-stressed group of students, they clicked randomly, but tended to stay AWAY from the choices that would deliver the food they were tired of. So if they had been exposed to a ton of chocolate pudding, they would prefer orange juice, and vice versa. However, in the case of the stressed group of students, something different happened. They had eaten either pudding or oranges to satiety, but because they were stressed, they picked their habit choices ANYWAY. They might be tired of pudding, but the stress seemed to make that choice that much easier, even when they weren’t getting anything out of it. They continued clicking away on the pudding choice out of habit until the trial stopped.
So what does this tell us? It tells us that stress can encourage people to keep choosing the things they’ve got a habit for, even if that habit is no longer rewarding. This seems pretty obvious when you think about smokers, who, when they are stressed, just need a cigarrette, even if that is no longer rewarding, or heroin addicts who just need a hit, even though they are so tolerant it may not do much for them.
And the effect really was habit. When they asked all the students afterward what the associations between shapes and rewards were, the unstressed students got most of them right. The stressed students actually couldn’t remember as well, they were acting out of habit even without an idea of what the actions themselves really meant.
So stress brings out the habit in us, which could be important for several reasons. It’s well known among addiction researchers that stress brings out drug craving, and this could be both a drug issue AND an issue with stress, with people wanting to indulge their habits (if your habits are things like shooting up heroin and smoking crack). It also could be an important thing to study for institutions like the military, where you need to be able to react in times of extreme stress. Perhaps the best training would involve people acting out of habit.
Of course, Sci is a total geek, and wonders something else. What impact could this have on people who, say, react differently to stress in a physiological manner. For example, there are some endocrine disorders which involve differences in cortisol production, a hormone responsible for a lot of the body’s (and thus the mind’s) response to stress. Would people with, say Addison’s disease have different reactions to stressful situations? Could they enforce cognitive learning over habit? And what effect, if any, did this have on JFK’s response to the Cuban Missile Crisis? Of course this is all silly thinking, but it does make Sci wonder if more people are doing tests on people with different responses to stress and their responses to habit-forming stimuli.
There are a few issues with this study that Sci can see. Do we know how long that cold water stress test lasts? Would differences have been bigger if they’d administered it twice, once at the beginning and once after eating to satiety? And the BIG issue: orange juice AS rewarding as chocolate?! WHAT?! Surely you jest. Even though some people may indeed prefer them both equally, one might imagine the physiological response to orange juice (straight up sugar) and chocolate milk (sugar, fat, and protein) are not going to be the same. If Sci was conducting this study, she’d have made them choose between orange and grape juice, or orange and apple juice. Fairly similar fluids, different tastes. Or, better yet, the difference between chocolate mint and chocolate caramel. Relatively similar but very distinct. Also very dleicious. I would totally sign up for that study.
Schwabe, L., & Wolf, O. (2009). Stress Prompts Habit Behavior in Humans Journal of Neuroscience, 29 (22), 7191-7198 DOI: 10.1523/JNEUROSCI.0979-09.2009

6 Responses

  1. I enjoyed reading this post, both for the content and your writing style. It should be obvious that stress triggers habitual behavior, but it is nice to see actually data on the effect.

  2. Yeah, sci’s writing style is a lot of fun. She should collaborate with an illustrator and write some coffee table books. Reckon she could target Charlie Brookers audience over here in the UK if she wanted to do TV not sure what audience there is in the states though since I haven’t access.
    It would be nice if people vying for power and opportunity plane spoke a bit more about the effects of negative and positive conditioning in stress situations. Really enjoy your blogs and placing a fair amount of hope in addiction studies breeding greater tolerance and concern for those in difficulty.

  3. Great post…

    It also could be an important thing to study for institutions like the military, where you need to be able to react in times of extreme stress. Perhaps the best training would involve people acting out of habit.

    Actually, a great deal of military training, both beginning (boot camp) and on-going is for just that purpose. All the focus on attention to detail, for instance, makes paying attention to detail a habit during the stress of combat. Similarly, practice in taking care of weapons, habit when on guard duty, etc.
    I suspect there have been some studies on this going back to the fiftys, if not before, but they may be classified.

  4. duh! except:
    strike “chocolate”
    replace with “dunkin”
    leigh’s n=1 in a more complex paradigm of less careful experimental design, so this is a more valid study anyway. really, it’s cool to see this in a systematic investigation, even if it is flawed.
    i also found orange = chocolate strange. not that i don’t like oranges a whole lot, but chocolate contains an entirely different nutritional profile. humans generally find sweets with fat content pretty rewarding. i wonder how the pathways involved in feeding behaviors tie in here.

  5. And the BIG issue: orange juice AS rewarding as chocolate?!

    Depends on the quality of the chocolate. If they were using the pudding equivalent of wax-lips-grade “chocolate”, then, yeah.

  6. This isn’t research if you’re being sponsored by a company that manufactures chocolate. It’s business.

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