Hello. It's a great honor to give this talk today.

How many of you would like to be successful in life?

Raise your hand. Alright?

Well actually, the two most important keys to success in life are:

intelligence, and self control.

Guess which one you can do the most about.

(Laughter)

Self control, right?

There are pills to cure just about everything,

but unfortunately, there are no pills to cure low levels of intelligence.

(Laughter)

My talk is going to focus on self-control.

In the 1960s and 70s, a Stanford psychologist

developed an ingenious way to measure self-control in children.

He put a marshmallow in front of them, and told the kids,

"You can eat it now if you want,

but if you wait until I come back, you can have two marshmallows."

He tested hundreds of kids,

and then did follow-up tests on them decades later.

And what he found is that kids who waited for two marshmallows,

were much more successful in life.

They had higher standardized test scores,

they were more likely to graduate from college,

they had happier marriages,

lower divorce rates,

lower obesity rates.

The kids who ate one marshmallow immediately, they all went to jail.

(Laughter)

Just kidding, just kidding.

They didn't go to jail.

But in one of these studies,

the researchers found that the kids who waited for two marshmallows,

had more activity in the pre-frontal cortex.

That's the part of your brain

in charge of, thinking, reasoning, and emotional control.

Psychologists call these 'executive functions.'

So poor self-control is actually responsible for many problems in life,

and many of these are preventable,

such as health problems,

eating unhealthy food, not wanting to exercise,

addictions to the internet or alcohol, tobacco, just to name a few.

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(Laughter)

People also have trouble controlling their finances.

Some people spend more money than they make.

Sometimes governments do this too.

(Laughter)

Some people have trouble controlling their sexual desires,

including some politicians.

(Laughter)

And this can lead to very difficult consequences.

And people also have trouble controlling their anger.

Indeed, anger is the emotion people have the most difficulty controlling.

(Laughter)

And sometimes anger can even lead to criminal behavior.

For example, by far the greatest cause of murder is anger.

(Laughter)

Really!

(Laughter)

No other cause even comes close, like drugs, nothing even comes close.

Anger is the leading cause of murder.

So speaking of criminal behavior,

two criminologists wrote a very influential book

called A General Theory of Crime.

What a brazen title!

What general factor could cause all crime?

Is it bad parenting?

Bad genes?

Substance abuse?

Poverty?

Frustration?

No, actually, the best predictor of criminal behavior,

especially violent criminal behavior,

is poor self-control.

So, for over 25 years, I've spent my career studying human aggression.

And aggression often starts when self-control stops.

What I'd like to do today

is tell you about a few studies that we've conducted

on the link between low self-control and aggression,

but before I do, I want to tell you a little bit more about the brain,

because, the brain plays such a critical role in self-control.

The human brain's about the size of a grapefruit.

And although it's only about two percent of our body weight,

it uses 20-30 percent of the calories we consume.

The brain is a very demanding organ.

Calories provide fuel for the brain that it uses for many functions,

including those executive functions I talked about earlier:

thinking, reasoning, and emotional control.

Also recall, that the emotion

people have the most difficulty controlling is anger.

Now food... gives us calories.

I don't know if you've noticed this or not,

but sometimes when people don't get enough food to eat,

they have trouble controlling their anger.

Hungry people tend to be cranky, irritable, angry.

How many of you know what I'm talking about?

(Laughter)

I thought so.

There's actually a term to describe this; it's called 'hangry.'

(Laughter)

Hungry plus angry.

Hangry.

Now we actually did the first experimental study

to test whether hangry is a real thing.

I'd like to point out, it's really important

that we use science to test what ideas are true and which ones are false,

rather than relying on hunches, intuitions, gut feelings,

common sense, instincts,

because those can differ dramatically, for different people,

and they can often lead us astray.

So I'd like to tell you about our experimental study on hangry.

Participants were college students.

They fasted for food and water

for three hours before they came into our lab.

That's a very long time for college students.

(Laughter)

First, they participated in what they thought was a taste test study,

and we randomly assigned them to drink lemonade

that was either sweetened with sugar,

which has calories and therefore provides fuel for the brain,

or the lemonade was sweetened with Splenda, a sugar substitute,

with no calories, and hence, no fuel for the brain.

In a blind test task, people can't tell the difference

between the lemonade sweetened with sugar,

and the lemonade sweetened with Splenda.

Then we had to measure aggression.

Well, this is kind of tricky, right?

Because researchers can't just give participants guns and knifes

and see what they do with them.

(Laughter)

So researchers have to come up with safer ways to measure aggression.

Now, aggression is any behavior intended to harm another person

who wants to avoid that harm.

And in this study, and in the studies I'll tell you after,

we used a noise blast procedure,

that I developed for my doctoral dissertation.

So let me tell you about this noise blast procedure.

In this procedure, participants compete with an ostensible opponent,

to see who can press a mouse button faster,

when a target square turns red.

The winner gets to blast the loser with loud noise through headphones.

(Laughter)

The noise levels range from level 0 to level 10.

We included 0 because we didn't want to force people to behave aggressively.

If they don't want to behave aggressively, they don't have to,

they can just choose 0.

Level 1 is 60 decibels, 2 is 65, 3 is 70, 4 is 75,

all the way up to level 10, which is 105 decibels.

That's about the same volume as a fire alarm

going off directly into your ears through headphones.

(Laughter)

The winner also gets to control how long the loser suffers

(Laughter)

by setting the noise duration, from 0 seconds to 5 seconds.

Now, the noise is a combination of noises that many people really hate,

like fingernails scratching on chalkboards,

dentist drills, blow horns, sirens.

And they do this task 25 times,

so we can get a more reliable measure of aggression.

So I know you're dying to hear this noise,

so actually, I have a sound level meter,

so I can tell you how many decibels this is.

Okay, so here you go.

(Screeching noise)

(Noise ends)

Do you want to hear it again?

(Audience) No!

93 decibels. 93!

It goes up to 105.

So, we told participants that the study

was about the effects of different kind of foods on a reaction time,

but it was not.

The study was about the effects of glucose on aggression.

And we explained this to participants after the study was over.

So here are the results

for participants who drank the lemonade sweetened with sugar,

and those who drank the lemonade sweetened with Splenda.

Those who drank the lemonade with Splenda

were significantly more hangry and aggressive.

Why?

Because the Splenda has no calories for the brain.

Well, we wanted to replicate this study; scientists like to do that.

We also wanted to see if the effects generalize,

because after all, this was a laboratory experiment.

It was conducted in an artificial setting - psychological laboratory.

Study lasted less than an hour.

And the participants were college students who aggressed against a complete stranger.

So, we conducted a field experiment as a follow up study.

In this field experiment, participants conducted the study in their own home,

a natural setting.

Study lasted 23 days, rather than less than an hour.

And the participants were actually married couples,

(Laughter)

who aggressed against their spouse.

(Laughter)

So, we had 107 married couples.

They'd been married about an average of 12 years,

and on Day 1, we brought them in our lab,

we gave them a standardized measure of marital satisfaction.

We wanted to control for this,

because couples who were satisfied with their marriage,

may be less angry and aggressive with their spouses than those who are not.

We also gave them a blood glucose meter; we showed them how to use it.

We sent them home with it, and for the next 21 days

they measured their blood glucose levels every morning before they ate breakfast,

and every evening, before they went to bed.

We also gave each person,

(Laughter)

a Voodoo doll, along with 51 pins.

We told them that this doll represented their spouse.

(Laughter)

Every night before they went to bed,

they stabbed between 0-51 pins into the doll,

(Laughter)

depending on how angry they were with their spouse that day.

They did this alone with their spouse not being present.

(Laughter)

And we actually developed this Voodoo doll task,

and we validated it in several studies involving couples.

We like it a lot because it's an objective measure,

you can count the number of pins between 0 and 51.

It doesn't use self-reports.

And it also takes some effort to put the pins in the doll.

One participant stabbed all 51 pins in the doll on one of the days.

Actually, on two of the days.

(Laughter)

Man, I'm glad I'm not married to that person.

(Laughter)

So, I bought 250 of these dolls; they're $20 each.

One day I got a call from my credit card company.

(Laughter)

They said, "Did you really spend $5,000 on Voodoo dolls?"

(Laughter)

I said, "Yeah, I did; I'm a scientist,

and I'm doing a study that involves over 200 participants,

and each of them gets a Voodoo doll.

And they said, "Really?"

(Laughter)

I said, "Yeah, really!"

They said, "Okay. It seemed like a suspicious charge to us.

(Laughter)

We never saw anybody spend $5,000 on Voodoo dolls before."

So on Day 23, we brought them back in the lab,

and they did the noise blast task that I described earlier.

Did you want to hear that noise again?

(Audience) No.

Okay, I didn't think so.

But this time, their partner was their spouse rather than a stranger.