Resisting temptation in the brain

Having spent the last three years studying how difficult it is to say no to our vices, and being intimately acquainted with all that can go wrong in fMRI research, I’m always a bit skeptical of studies that claim to be able to predict our capacity for self-control based on a brain scan. But a new paper out this week in Psychological Science seems to have done a pretty admirable job, tying our real-life ability to resist temptation with activity in two specific areas of the brain.

Researchers from Dartmouth University first tested 31 women on two different tasks: an assessment of self-control and a measurement of temptation. Using an fMRI scanner, they compared where the women’s brains lit up when they were stopping themselves from performing a certain action (pressing a button, to be exact), and when they were seeing images of ice cream, hamburgers, and other tasty treats. As expected, better performance on the response inhibition task was linked to activation in a part of the brain called the inferior frontal gyrus (IFG), a region in the frontal cortex known to be involved in inhibiting a response. Conversely, looking at pictures of chocolate and chicken sandwiches activated the nucleus accumbens (NAcc) a deeply rooted part of the brain that’s essential in feelings of reward.

So far, this is all pretty par for the course; you exert self-control, you activate your control center. Looking at something enticing? Your reward region is going to light up. Nothing new or ground-breaking (or even that useful, to be honest). But the researchers didn’t stop there. Instead, they took the study out of the lab to see what happened when the participants were faced with real-life temptations. Equipping them with Blackberry smartphones, the participants were prompted throughout the week with questions about how badly they desired junk food, how much they resisted these cravings, whether they gave in to their urges, and how much they ate if they did cave to temptation.

Comparing these responses to brain activity in the two target areas, the researchers discovered that the women who had the most activity in the NAcc while viewing images of food were also the ones who had the most intense cravings for these treats in real life. Additionally, these women were more likely to give in to their temptations when they had a hankering for some chocolate. On the other hand, those who had greater activity in the IFG during the inhibition task were also more successful at withstanding their desires — in fact, they were over 8 times more likely to resist the urge to indulge than those with less activity in the region. And if they did give in, they didn’t eat as much as those with a smaller IFG response.

Having confirmed the link between activity in these areas and real-life behaviors, the next step is to figure out how to ramp up or tamp down activity in the IFG and NAcc, respectively. One technique that psychologists are exploring is transcranial magnetic stimulation, or TMS. This involves zapping a certain part of the brain with an electromagnetic current, trying to either stimulate or depress activity in that region. So far, use of TMS in studies of addiction and eating disorders — attempting to enhance self-control and decrease feelings of craving — has been met with limited success. Pinpointing the exact right area through the skull and figuring out the correct frequency to use can be difficult, and in fact, a few studies have actually accidentally increased desire for the substance! Additionally, the effects are often temporary, wearing off a few days after the stimulation is over. Other studies have looked at cognitive training to try to enhance self-control abilities, particularly in children with ADHD, although these attempts have also varied in their success.

Beyond targeting certain psychiatric disorders or trying to get us to say no to that second (or third or fourth) cookie for reasons of vanity, there’s a push to enhance self-control from a public health standpoint. The authors of the current study cite the staggering statistic that 40% of deaths in the U.S. are caused by failures in self-control. That’s right, according to research, 40% of all fatalities are caused by us not being able to say no and partaking in some sort of unhealthy behavior, the biggest culprits being smoking and over-eating or inactivity leading to obesity. Clearly then, improving self-control is not only needed to help individuals on the outer edges of the spectrum resist temptation, it would benefit those of us smack dab in the middle as well.

Happy Friday!


Salivating for stocking stuffers

In the spirit of this season of holy consumption, I thought it appropriate to write about an article released earlier this year in the Journal of Consumer Research on salivating over material goods. Author David Gal, an economist at Northwestern University, proposes that when we covet an item, be it ice cream or an iPhone, we literally drool over it. He hypothesizes that this response mechanism is caused by our reward system, with desired material items stimulating the same pathways and neural regions that hunger for food or other natural reinforcers do. This includes the striatum, amygdala, and hypothalamus–areas involved in reward responses and homeostatic mechanisms such as hunger and satiety. Activation of these areas in response to salient stimuli signals that these items are rewarding and could be important for survival. Supporting this claim, in previous research, the mesolimbic dopamine reward pathway is seen to light up in a similar manner for luxury items and sports cars, which are secondary learned reinforcers, as they do for natural incentives such as food and drugs.

Taking this a step further, the physical outputs of this heightened reward arousal state can include the secretion of saliva, triggered by the sympathetic and parasympathetic nervous systems. Salivation occurs in response to cues for food or water as part of the natural metabolic system, preparing us for mastication and digestion. However, Gal claims that it is also a byproduct of the autonomal arousal system controlled via the hypothalamus, and salivation can indicate any desired or salient stimulus, whether it be naturally rewarding, such as a member of the opposite sex, or a secondary conditioned reinforcer, like money or material goods.

Gal investigated this theory by presenting 169 undergraduate students with images of either money or mundane items, such as office supplies. While viewing the stimuli, participants were asked to keep cotton dental rolls in their cheeks and under their tongue to measure their saliva output. The weights of these cotton swabs were then compared to baseline measurements taken before the experiment to assess the increase in salivation due to the images presented. A second condition involved priming participants with feelings of either efficacy or helplessness by asking them to recall a time when they had felt either powerful or powerless. Gal hypothesized that money, symbolizing economic control, would be more coveted by those who felt they had little power, making it more desirable and rewarding than to those who deemed that they had greater power at the time of the experiment. Supporting this notion, only participants induced with feelings of powerlessness had significantly increased saliva output in response to the monetary cues. Individuals who felt powerful had no difference in salivatory rates when viewing the money images, nor was there a difference in saliva outputs in either power condition among participants in the control office supply group.

In a second follow-up study, Gal repeated the experiment using coveted luxury items in the place of raw currency. Gal exposed young men to images of sports cars, while also inducing in them the goal of winning a potential mate. He achieved this by presenting some participants with images of attractive women with whom they were to imagine going on a date with, while those in the control condition were to imagine having their hair cut. Men who viewed the sports cars as opposed to the mundane images had greater salivation rates compared to baseline ratings, but only when they had been primed with the goal of mating. The mating prime had no effect on saliva output in the control condition, and viewing the sports cars without the salient goal did not increase salivation rates on its own.

Importantly, increases in saliva production seem to be contingent upon the immediate rewarding value of the goods, only enhancing salivation rates when the presented stimuli were seen to help achieve a recently primed goal. This suggests that the triggering of salivation by reward cues is dependent upon the present desire or need for the item, much like the more visceral feeling of hunger in the presence of food.

So as you are finishing your Christmas wish-list this year, dreaming of drool-worthy duds and mouth-watering machines, perhaps rank your heart’s desire on how quickly they’ll come in handy and how moist your mouth feels afterward. You’ll be sure to find them more rewarding.

Happy holidays everyone!

(Thanks to Emily Barnet for this article.)