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Red area shows location of mirror neurons in the ventral premotor cortex, the part of the brain responsible for coding object-oriented movements such as grasping, holding, and manipulating. This region lies adjacent to the primary motor cortex, which sends electric signals to the muscles.

Marco Iacoboni

What do people really do all day, every day? We “read” the world. And much of the world consists of other people. When a tennis player raises his racquet, for example, you know instantly whether he’s going to take a practice swing or throw his racket across the court in anger. We all make dozens—hundreds—of such distinctions every day. It is, quite literally, what we do, usually without a second thought. It all seems so ordinary.

In fact, it’s extraordinary—and even more extraordinary that it feels ordinary! We achieve our very subtle understanding of other people thanks to certain collections of special cells in the brain called mirror neurons. They are at the core of how we navigate through our lives. They bind us with each other, mentally and emotionally.

Mirror neurons are incredibly powerful; “vicarious” would not be a strong enough word to describe their effects. When we watch movie stars kiss onscreen, some of the cells firing in our brains are the same ones that fire when we kiss our lovers. And when we see someone else suffering or experiencing pain, mirror neurons help us to read her or his facial expression and make us viscerally feel the suffering or the pain of the other person. Those moments, I will argue, are the foundation of empathy (and possibly of morality). Research on mirror neurons gives anyone interested in how we understand one another some remarkable food for thought.

Consider the teacup experiment I published an account of in 2005 [see illustration below]. Test subjects are shown three video clips involving the same simple action: a hand grasping a teacup. In one clip, there is no context for the action, just the hand and the cup. In another, the subjects see a messy table, complete with cookie crumbs and dirty napkins—the aftermath of a tea party, clearly. The third video shows a neatly set table, in apparent readiness for the tea party. In all three video clips, a hand reaches in to pick up the cup. Nothing else happens, and the grasping action observed by the subjects in all three versions of the experiment never changes. Besides the difference in context, there is only one other variation: in the “neat” scenario the cup is full, whereas in the messy one the viewer cannot tell if the cup contains liquid.

Do mirror neurons in the brains of the subjects notice the differences in context and in the contents of the cup? Most definitely. When a subject observes the grasping scene with no context at all, mirror neurons are the least active. The neurons are more active when the subject watches the after-tea-party scene, but they are most active during the neat, full-cup scene. Why? Because drinking is a much more fundamental intention for us than cleaning up. The teacup experiment—now well known in the field of neuroscience—belongs to a wealth of recent empirical evidence suggesting that our brains are capable of mirroring the deepest aspects of the minds of others at the fine-grained level of a single brain cell. Reading the intention of others is only one example of the kinds of distinctions that can be made with a remarkable lack of effort. We do not have to draw complex inferences or run complicated algorithms. Instead, we use mirror neurons.