between observing action and understanding emotion. This link has been most clearly demonstrated in the case of facial expressions — if I observe the muscles of the face in a position to convey an emotional state, clearly I perceive the emotion. What has been shown recently is that observing such facial expressions leads to two kinds of brain activations in the observer: The first set of regions activated are those that would be used by the observer to execute the identical face movements, just as with hand or mouth movements. However, additional regions are also active, and these are precisely the ones that would be involved if the observer were to feel the observed emotion personally. Thus the circuitry for action observation in the human brain is interdependent with parts of the brain critical for understanding more complex nuanced aspects of the world.
Mirror Neurons
It turns out that there may be cellular building blocks in the brain that are particularly important for observing and executing actions, and may ultimately lead to an explanation of action understanding and imitation- based learning. In fact, such structures would contribute to any form of understanding that could be partly explained by imagined re-enactment of perceived actions (e.g., seeing an emotional facial expression, hearing a cry of pain). The cells under discussion are a type of nerve cell, or neuron, discovered in the front part of the monkey brain by Professor Giacomo Rizzolatti and his colleagues at the University of Parma. The scientists trained monkeys to perform specific actions like grasping an object or licking their lips, and were performing electrical recordings in regions in the front of the
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brain known to coordinate movements. These recording machines note brain activity both visually, as a graph on a screen, and auditorily, by a loud series of clicks, indicating the firing of a neuron. Rizzolatti and his team were focusing on a particular region in the front of the brain, and were having the monkey perform all sorts of hand, mouth, and eye movements to see how the brain cells were organized to make these movements happen. One day (or so the story goes), one of the researchers returned from lunch while the electrical recordings were being made, and was finishing off a cone of superb Italian gelato, when all of a sudden the recording device starting making a loud series of clicks. The returning scientist stopped licking his ice cream cone to see what was going on, and the noise stopped. When he restarted licking his gelato, the clicks resumed, and when he stopped again, they stopped. The investigators had discovered a type of neuron that was sensitive to the monkey observing a particular human action.
It was not surprising that following training to perform an action, some neurons in the motor region of the brain responded while performing that action, when the same neurons would not have responded beforehand. However, it was extremely surprising to find that some of those neurons also responded vigorously when the monkey observed the very same learned actions. Through a methodical and systematic approach, this group was able to make a more elaborate and far-reaching set of observations. For a small subset of neurons, if a monkey had learned to reach for a particular object, seeing another monkey reach for the same object would cause the neuron to fire. For a different subset of neurons, if the
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