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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

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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