God Soul Mind Brain

fingers. A library of complicated, coordinated grasps was apparently stored in this particular area of the motor cortex, triggered by the activity of one or another set of neurons. Neurons of this type are sometimes called command cells—cells that command a fully coordinated, complicated piece of behavior.

    The grasp cells, by themselves, were already an important discovery. Then Rizzolatti and his colleagues noticed a strange new property while they were studying a grasp neuron in a monkey. At some point during the experiment, the human experimenter picked up a small piece of food to place it within reach of the monkey. As the experimenter grasped the food, and as the monkey watched the experimenter, the monkey’s own grasp neuron became active. The neuron was just as active watching someone else grasp as it was when the monkey himself grasped. In essence, the neuron was shouting out the signal, “A grasp is occurring!”

    One way to interpret this neuron is that it was a motor control neuron, normally involved in controlling grasp. When the monkey saw somebody else make a grasping movement, the monkey mentally imitated the same act, and this neuron participated in the mental mimicry.

    Rizzolatti and his colleagues named this type of neuron a “mirror neuron”—a neuron that responds whether a specific action is performed by the monkey or observed by the monkey. Some mirror neurons represent a precision grip, some represent a whole-hand grip, some represent the act of tearing a piece of paper in half, and so on. A wide range of actions related to the hands have corresponding mirror neurons in this particular region of the monkey motor cortex. Mirror neurons were then discovered in a second region of the monkey brain, also shown in Diagram 8-1. These two mirror neuron areas are directly connected to each other, sending signals back and forth, forming a larger system for mirror neurons.

    After the discovery in monkeys, mirror neurons were found in the human brain. Strictly speaking, nobody has studied the individual mirror neurons in the human brain, although technically the experiment is possible. It would require inserting an electrode into the human motor cortex and measuring the activity of individual neurons. If a person were about to undergo brain surgery in that area of the cortex, and electrodes were going to be used for medical reasons, then the experiment would be ethical. However, it seems that relatively few brain surgeries involve the motor cortex. Instead, the less precise but much pleasanter method of brain scanning has been used. Volunteers are placed in a brain scanner, and general regions of brain activity are measured noninvasively through the skull. Roughly the same area of cortex becomes active whether the participant grasps a peanut or watches a video of someone else grasping a peanut. The mirror neuron system exists in humans just as it does in monkeys.

    Mirror neurons have become one of the hottest industries in current neuroscience. But what exactly is the contribution? What insight have we gained by the discovery of mirror neurons? The debated question used to be: do people constantly mentally mimic the actions (particularly speech) of other people? Lacking any way to spy into the mind, and therefore lacking any evidence, the consensus answer used to be: probably not. When Rizzolatti discovered mirror neurons, he found himself spying in on the brain’s act of mental, sub-threshold, subtle imitation. Mental imitation exists. It is now generally accepted that our motor systems rev up, mentally rehearsing pretty much every action that we watch another person performing. Mental imitation is the norm, not the exception, for monkeys and humans.

    The idea of mental imitation is now being pushed beyond the simple case of grasping a peanut or ripping a piece of paper. Here are a few examples.

    You watch someone accidentally walk into a tree. What do you do? You grimace, squint, suck in your breath, duck your head, and put your hand up to your face. You produce the defensive actions that you expect the other person to produce.

    You see someone smiling—a real, genuine, warm smile. Not only do you tend to smile, but you actually feel a little bit happier. You are imitating not only the motor act, but the emotional state that you perceive in the other person.

    You watch a public speech. The speaker drops his notes and makes a horrible mess of the delivery. You do more than merely note