magazine issue 10 2007 / Issue 5

On Mirror Neurons or Why it is Okay to be a Couch Potato

• written by Daniëlle van Versendaal

Have you ever wondered why, when you see someone stretch out and yawn, suddenly, you start to feel drowsy and feel the urge to do the same? Or how about the tendency of people to copy each other’s postures? In social psychology this phenomenon is called postural mirroring. All this mimicking is the result of so-called mirror neurons in our brain.

One example is the way our face crumples (as depicted above) when we see someone eating sour food such as a lemon. It is almost like we are experiencing the same thing. In fact, our brains are representing the internal state of others. Our mirror neurons enable us to learn certain movements, think about dancing classes and even to empathise with the people around us.

The Scientific Discovery of Aping

About 15 years ago mirror neurons were discovered serendipitously at the University of Parma in Italy. Researchers Giacomo Rizzolatti and Vittorio Gallese were initially studying the planning of movements in monkey brains. They first found that specific neurons responded when specific actions were performed. For instance a subset of neurons were active when the monkeys grasped for a peanut and other neurons that started firing when they actually chewed on a peanut.

One day, on of the researchers reached out for a peanut to give to the monkey. They then saw the same neurons in the monkey’s brain starting to fire as if it was reaching for it himself. There was almost no difference between a monkey’s brain reaching for a peanut or a monkey observing a human being doing the same thing. Rizzolatti and Gallese published their findings in 1996 in the scientific journal Brain and termed their discovery mirror neurons (Gallese, Fadiga, Fogassi & Rizzolatti, 1996).

Mirror neurons are active when someone observes a movement as well as when someone performs the act himself. The same is true for the facial expression of emotion, which is why links have been made between mirror neurons and empathy. Also, researchers now have come to realize that mirror neurons as such probably are not a type of cell in the brain. Instead, mirroring is thought to be an emergent property of the network structure of the brain. We therefore sometimes also talk about the mirror system.

The brain area of interest to the Italian researchers is the premotor cortex, a brain area involved with the planning of our movements. The premotor cortex is connected to the motor cortex which controls our muscles and therefore movements. Thanks to the work of a famous neurosurgeon, Wilder Penfield, we now know a lot about the anatomy of these brain structures. When he operated on the brains of epilepsy patients, he stimulated their cortex with small electrical pulses and saw their limbs moving as a result. He mapped this brain area and showed the precise topography of each body part represented by a specific part of the cortex.

The anatomy of the motor cortex: a large bulge (called a ‘gyrus’) spanning across the entire hemispheres of the brain. Every part is controlling a specific body part. Note that especially our hands and face are controlled by a proportionally large part of our brain. This shows how expressive our faces and fine our manual motor skills are. The premotor cortex where the mirror system was first discovered lies just in front of the motor cortex these two areas are well connected.

A lot of attention has been given to the mirror system since its discovery. It is also studied in human subjects. In their minds, people perform the actions they observe. Mirroring properties in humans have been found in the premotor cortex, and additionally, the parietal lobes show similar involvement, especially when the mimicking of emotions is involved (Gallese & Goldman, 1998).

Our Brains in Action

Sometimes, we can see mirror neurons in action. For instance, when we copy each other’s posture, facial expression or sometimes even accents are unconsciously mirrored. When our brain acts after observing the actions of others, neurons in the premotor area have activated our actual motor cortex. The more attention someone gives to an act of observation, the more likely that person will copy the behaviour they see. There is a theory in social psychology that when people mimic each other’s posture they like each other. The other way around works as well, copying someone, providing it’s done unconsciously, makes you more attractive and likeable.

When we are watching sports on TV, our premotor and motor cortices are constantly active. There is strong evidence that watching sports heightens our muscle tension very slightly. Our mirror system is therefore the ideal excuse for not going to the gym, but watching a game instead, sitting comfortably on your couch.

More recently, it was found that even hearing about movements can activate our premotor cortex (Aziz-Zadeh, Lacoboni, Zaidel, Wilson & Mazziotta, 2004).It is suggested that our mirror system might have been involved with the development of language. Let’s experiment!

If I tell you “Stretch your right leg” do you feel inclined to do so?

Sports can be very healthy and watching it just as strenuous. Thanks to your mirror system you never have to feel guilty again for being a bit of a couch potato, your premotor cortex is constantly moving.

References

Aziz-Zadeh, L., Iacoboni, M., Zaidel, E., Wilson, S. & Mazziotta, J., (2004). Left hemisphere motor facilitation in response to manual action sounds. European Journal of Neuroscience, 19, 2609–2612.