IF THERE IS ANYTHING about your “self” of which you can be sure, it is that it is anchored in your own body and yours alone. The person you experience as “you” is here and now and nowhere else.
But even this axiomatic foundation of your existence can be called into question under certain circumstances. Your sense of inhabiting your body, it turns out, is just as tenuous an internal construct as any of your other perceptions—and just as vulnerable to illusion and distortion. Even your sense of “owning” your own arm is not fundamentally different—in evolutionary and neurological terms—from owning your car (if you are Californian) or your shotgun (if you are Sarah Palin).
Outlandish as such a notion may seem, what you think of as your self is not the monolithic entity that you—and it—believe it to be. In fact, it is possible to pharmacologically manipulate body ownership with a drug called ketamine, which reliably generates out-of-body experiences in normal people. Patients on ketamine report the sensation of hovering above their body and watching it. If someone gives them a sharp poke, they might say, “My body down below is feeling the pain, but I don’t feel it myself.” Because in such patients the “I” is dissociated from the body it inhabits, they do not experience any agony or emotional distress (for this reason, ketamine is sometimes used as an anesthetic).
Your sense of body ownership, and of being a distinct entity, seems to derive in part from a network of brain cells known as mirror neurons. Located in the premotor cortex, they interact with your prefrontal cortex, the part of the brain that makes plans and decisions. Ordinarily, when you move your hand to, say, reach for a pen (a motion that is accompanied by your sense of having free will), certain motor-command neurons in the motor cortex fire. Intriguingly, as Giacomo Rizzolatti of the University of Parma in Italy and his colleagues Marco Iacoboni and Vittorio Gallese have demonstrated, some of these neurons also fire when you merely watch another person perform the same action.
Mirror neurons allow you to put yourself in another person’s shoes. Your brain says, in effect, “The same neurons are firing as when I move my hand, so I know what he is feeling and what he is up to.” In addition, neurons we might loosely call “touch mirror neurons” fire when you are touched or watch someone else being touched. That humans have these abilities made intuitive sense to Charles Darwin, who noted that when you watch a javelin thrower about to release the spear, your leg muscles flinch unconsciously and that when a child watches his mother use a pair of scissors, he clenches and unclenches his jaws in uncontrollable mimicry. In this phenomenon we see an evolutionary prelude to the ability to imitate and emulate—the basis of cultural transmission of knowledge.
Yet as you grow to adulthood, you no longer irresistibly mime the actions of whomever you happen to be looking at; your self doesn’t feel like a puppet controlled by others. You preserve your sense of free will and agency (although patients with Tourette syndrome do sometimes engage in unconscious mimicry).
The tendency to unconsciously mimic the person you are with is normally inhibited by your prefrontal cortex (the most evolutionarily advanced part of the brain, which is pronounced in humans). We recently suggested in an essay on the Edge Foundation Web site (www.edge.org) that interactions between the mirror neuron system and feedback from the prefrontal cortex is what gives the self its peculiar dual character of simultaneously maintaining individuality and reciprocity with others.
Derangements in this system would lead to out-of-body experiences, which may explain the mechanism of ketamine. Under its influence you “empathize” with your body the same way you empathize with other people, and you are able to simultaneously detach yourself from it—just as you detach yourself from others.