A possible link between pollution and crime—and marshmallows

At Wired, Jonah Lehrer delves into an interesting theory about why American crime rates have fallen so drastically over the last 30 years. Apparently, there is both a correlation and a mechanism that would seem to connect falling rates of a certain kind of environmental pollutant to the downward trend in crime statistics. It all comes back to one of my favorite experiments in the annals of behavioral psychology. I'm speaking, of course, of the marshmallow test.

In the late 1960s, psychologist Walter Mischel left pre-schoolers alone in a room with a marshmallow. He gave the kids a choice: Eat your marshmallow now, and it's the only one you get. Resist temptation, and you'll be given two marshmallows to eat later. It's a classic test of delayed gratification and self-control. And only 20% of Mischel's test subjects managed to get the second 'mallow. Their secret: Distracting themselves with other activities, like singing or playing a pretend game.

But here's the interesting thing I didn't know—Mischel has followed those marshmallow kids over the course of their lives. Today, we know that the 20% who could hold out for a second marshmallow also had higher SAT scores, more friends, and fewer anger management issues as teenagers. And, thanks to brainscans, we can actually see differences between the adult brains of the 20% and their less self-controlled counterparts. In particular, Lehrer writes, the 20% demonstrate more activity in "the frontal cortex, [including] areas such as the dorsolateral prefrontal cortex, the anterior prefrontal cortex, the anterior cingulate, and the right and left inferior frontal gyri."

How does this tie back to crime and pollution. Turns out, those are also regions of the brain known to be particularly (and detrimentally) affected by early childhood exposure to lead. Medical researchers have long known that decreased impulse control is a common side-effect of lead-related brain damage. And, during the time that America's crime rates have fallen, so too have the levels of lead in our bloodstreams. According to this theory, environmental regulations that banned things like leaded gasoline and paint might be partly responsible for the fact that the murder rate in many American cities has fallen by 50%.

What Mischel's data demonstrates is that attention isn't just about information. Instead, it's also what allows us to blunt the urges of our errant emotions, allowing us to look past the desire to stuff that yummy marshmallow into our mouth. While we can't always control what we feel – many of our urges are ancient drives, embedded deep in the brain – we can control the amount of attention we pay to our feelings. When faced with a tempting treat, we can look away.

This returns us to aggression. Let's say you're being teased by a bully at school. You can feel your anger rising; the hot emotion is vibrating in your veins. It would feel so good to punch that bully in the face, to vent your frustration with a fight. However, you also know that such violence will get you suspended from school, which is why throwing a punch is not a good idea. If you can't strategically allocate your attention – and this is a skill that requires a solid prefrontal cortex – then you're not going to be able to resist your anger. You're going to get in a fight and get suspended. However, if you can properly look past this negative emotion – perhaps by counting to ten, or just walking away, or finding something else to think about – then your anger will subside. The hot feeling has been cooled off.

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