One of our writers was recently discussing human behavior with a colleague while stuck in traffic. The subject of why seemingly smart people do stupid things—things they know are morally wrong—came up, and our writer said he knew how it happened.

You see, our writer said, people have three brains.

His colleague looked at him with a smirk of disbelief on her face.

No, it’s true, he said. People have three brains, and each brain controls a different function in the body.

His colleague didn’t change the doubtful look on her face, but our writer continued.

We all have, buried deep down in our heads, a reptile brain. The reptile brain is responsible for the most basic bodily functions like breathing and keeping your heart pumping. It also seeks out the basic things the species needs for survival: food, air, water and, well, a mate. It controls our fight or flight reaction.

The colleague still wasn’t buying it.

The reptile brain is very tiny. Lying on top of it is the much bigger mammal brain. That’s where emotions live. Dogs have both reptile and mammal brains. It’s where their sense of loyalty comes from.

The colleague was waiting for the punch line. Undeterred, our writer continued.

Finally, humans have a very large brain that lies on top of the mammal and reptile brains. It’s responsible for reasoning and logic.

The problem, our writer explained, is that the three brains don’t get along well, or even communicate.

For example, when presented with an apple pie, our reptile brain tells us that we should eat it. All of it. It contains scarce resources that aren’t easily found in the wild: fat, salt and sugar. And while the reptile brain is small, it’s powerful, persistent and persuasive.

Our mammal brain tells us we’d feel guilty if we ate the entire pie and didn’t share it with anyone else. It also tells us that we’d feel very happy and satisfied if we ate some pie.

Our human brain tells us that pie is bad for our waistline. It contains lots of calories and cholesterol from all the butter that makes the crust so deliciously flaky (there’s the reptile brain butting in).

When you swap out apple pie for a flirting colleague on a long business trip far from home, you can see how an especially persistent reptile brain might get one in trouble.

The colleague wouldn’t hear any of it, and our writer certainly wasn’t condoning immoral behavior. But his argument was true—psychologists have long known about the different parts of the brain, how they developed from an evolutionary standpoint, and which functions they control. And they understand how certain images, words and stimuli can be used to control and direct human behavior by tapping into these different parts of the brain.

Marketers know this, too. That’s why during televised football games, for example, we’re bombarded with ads designed to stroke our reptile brain: “feed me”-type messages that convince our fat, sugar and salt-loving reptile brain that we really do need that delivery pizza after all.

Corporate communicators can use this to their advantage as well, but hopefully in less sinister ways. By understanding how consumers respond to various stimuli, one can craft more powerful messages that resonate strongly with the target audience.

In my next post, I’ll give some examples of how this can work for you.