Smiles are contagious.

And no, that's not just what mom tells you as she carts you off to school, assuring you that you'll make plenty of friends. Just keep smiling.

In fact, scientists have long noted that animals reflect each other's expressions — smiles, frowns and everything in between — as an essential means of communication.

Rhesus macaques, for instance, can intuit each other's mental states based on their expressions — and, more importantly, they can mirror them.

So too, researchers claim, can we.

It all comes down to a special kind of brain cell identified by Italian scientists back in 1992 called a mirror neuron.

These neurons communicate from person to person, or primate to primate, essentially mirroring each other's expressions and the feelings that go along with them. Ultimately, they may form the pillars of empathy.

Here's how neuroscientist Marco Iacoboni expressed it in a 2008 interview with Scientific American:

"When I see you smiling, my mirror neurons for smiling fire up, too, initiating a cascade of neural activity that evokes the feeling we typically associate with a smile. I don't need to make any inference on what you are feeling, I experience immediately and effortlessly (in a milder form, of course) what you are experiencing."

A diagram showing how mirror neurons work. Mirror neurons are also known as 'monkey see, monkey do' cells. (Photo: VectorMine/Shutterstock)

While some scientists have hailed mirror neurons as "the basis of civilization," others suggest their role may be somewhat overrated.

There's little doubt, however, that the discovery of mirror neurons represented a shift in our understanding of how we communicate.

Before then, scientists figured we interpret other people's actions using strictly logic. That person is smiling. Hence, she must be happy.

(Never mind that smiles can be produced independently of feeling.)

But mirror neurons suggest we can understand a person's inner thought processes on a biological level. We don't consciously deduce their state of mind. We feel them. And we simulate them.

Ever see someone stub their toe? You probably recoiled in your own phantom pain. Those would be the mirror neurons firing. Or, maybe you've seen someone exuberantly happy. You don't know the reason for their joy, but you feel it too. Again, mirror neurons.

"Mirror neurons are the only brain cells we know of that seem specialized to code the actions of other people and also our own actions," Iacoboni explained in Scientific American. "They are obviously essential brain cells for social interactions. Without them, we would likely be blind to the actions, intentions and emotions of other people."

And not just people. Our mirror neurons may extend also to animals. Maybe that accounts for why some people can't drive past an injured animal on the road — even after countless people already did?

Perhaps, those firing mirror neurons are the source of empathy — and the better they function, the better we're able to relate to our fellow living beings.

But there's a flip side. What happens when the mirror neuron system is on the fritz? Research suggests there's a link between autism and misfiring neurons. A 2005 study from the University of California, San Diego, for example, looked at 10 people with autism. The researchers noted their mirror neurons didn't function in a typical way but rather responded only to what they did themselves, rather than to the actions of others.

"The findings provide evidence that individuals with autism have a dysfunctional mirror neuron system, which may contribute to many of their impairments — especially those that involve comprehending and responding appropriately to others' behavior," study co-author Lindsay Oberman noted in a press release.

But mirror neurons may serve a purpose far beyond empathy. They may also be key to learning a language or skill. As any teacher will tell you, a language can't strictly be taught from a textbook. It has to be heard and absorbed and mirrored.

The same goes for learning to play guitar. Let the instructor play for you.

And, as your mom might remind you, the same may be said for a smile. If you send one out there, you'll get one back.

Good vibrations, indeed.

What are mirror neurons, and how do they make us more empathetic?
Mirror neurons help us imitate each other's expressions and the feelings that go with them.