S'more (Todd Bennett/Knight Ridder Tribune)

Remember those poor little kids who just couldn't wait for the Psych professor to come back into the room before they ate the marshmallow? You know, the ones with little to no self-control, who would go on to do more poorly in school, to be less "socially competent" adolescents and to be more prone to being overweight, divorce and substance abuse as young adults?

Well, they're back, and so are their goody-two-shoes peers who got an extra treat because they could seemingly go for hours without so much as nibbling on that marshmallow after the investigator left the room. 

Those kids are all in their mid-40s now, and you know what? They haven't changed a bit. At least, that's what the authors of a new study on the kids, published this week in the Proceedings of the National Academy of Sciences, say.

Their study also says that the ability to delay gratification -- a phrase this original group of researchers brought into the popular lexicon in the early-1970s -- seems to be one of those character traits that varies little over the life span, and that seems to correspond to differences in the way the brain functions in response to alluring temptations.

In short, we may just be born that way. (So go ahead: Eat the marshmallow!)

This they learned by bringing back two groups of the now-grown kids who participated first in the psychological experiments in the late 1960s and early 1970s, when they were between 3 and 5. These adults were at the extremes: One group of 32 came from the original group of kids showing the strongest ability to delay gratification; the second group of 27 was drawn from those children most likely to gobble up the marshmallow within seconds of the investigator's departure from the room, thereby forfeiting the extra treat awarded to good little waiters.

This time, researchers led by neuropsychologist B.J. Casey of Cornell Weill Medical College, decided that even weak-willed 40-somethings could probably resist a marshmallow. Instead, they dangled in front of the adult subjects an alluring social temptation: pictures of adult faces likely to attract their attention and hold their interest, with smiles and other displays of strong emotion, including fear. 

But while the subjects watched the slideshow, they were assigned a competing task that measured their ability, in a minority of instances, to hold back a trained impulse -- in this case, to push a button. Performing the task successfully demands not only rapt attention and intellectual control; it also requires subjects to resist the natural human temptation to gaze at faces showing compelling emotions. 

True to form, the adults who as children had demonstrated the highest degree of willpower still had it; they performed the task with greater accuracy than their peers who showed less sel- control as tots. The easily-led astray group -- called "low-delayers" -- was especially drawn off task when the faces were happy -- a naturally greater lure to most people.

Then, researchers put 15 of the people with a strong ability to delay gratification and 11 "low-delayers in a brain scanner and watched as they performed the toughest tasks from the first experiment.

When the temptation to gaze at the faces was strongest, the ventral striatum, a region of the brain associated with reward-seeking and impulse-choice behavior, became much more active in subjects with a record of low self-control than in those with good self-control. And compared to the low-self-control group, the more disciplined types had far more activity in their brains' inferior frontal gyrus. That is a part of frontal cortex that has been found to play a key role in inhibiting impulses and focusing attention.

B.J. Casey, who says she's pretty sure she would one of those low-delayers, says the statistical differences between these two groups were significant, but not huge. Yet, in the subjects' behavior, the differences were quickly evident to researchers. And in the real world -- especially in the teen years, when the allure of risk beckons every kid more strongly -- even little differences can mean a lot.

For low-delayers, she said, this persistent difference is not merely a weaker ability to resist impulse; these experiments collectively showed that for low-delayers, the drive to try, eat, buy or acquire alluring things seems to be stronger than it is for high-delayers. That may make them somewhat more vulnerable to addiction and obesity, she acknowledged. But it may also make them the risk-takers, the beauty-seekers and the trail-blazers of the world, while high-delayers knuckle down and gut their way through the tough stuff.

Want to see a bunch of parents' earnest efforts to discern whether their kids can resist a marshmallow? Check these out.