Mirror neurons: reflecting the pain of others?

Why do we sometimes wince or feel faint-hearted when we see another person being injured? Recent discoveries are helping neuroscientists begin to explain the brain mechanisms underlying the empathy we feel towards the pain of others.

Functional neuro-imaging has shown that imagining a scene (a cow eating grass in a field, for example) activates the visual cortex despite the absence of sensory stimuli. There could be an analagous situation in the somatosensory cortex, one of the brain regions which interpret tactile information and pain. If this were the case, the thought of a painful experience, or the observation of someone else in pain, could engage the somatosensory cortex, making that person feel faint-hearted or perhaps experience a painful sensation themselves, even in the absence of any tactile stimuli.

Evidence that this might occur comes from a collaborative study carried out last year at UCL's Institute of Cognitive Neuroscience, in which it was found that a woman experienced the sensation of being touched when she observed another person being touched.

The discovery of a type of cell called the mirror neuron may also help us to understand the brain mechanisms behind these phenomena.

Mirror neurons were discovered by Giacomo Rizzolatti and his colleagues at Parma University. Rizzolatti found that these cells, located in area F5 of the premotor cortex, fired not only when macaque monkeys grabbed an object, but also when they observed another monkey, or a human, grabbing an object.

The human brain is now known to contain its own mirror neuron system, located in the premotor cortex, superior temporal sulcus and the parietal cortex, all of which are connected either directlyor indirectly to the somatosensory cortex. Mirror neurons may therefore provide an explanation, at the cellular level, of how we empathize with the pain of others.

Our species is a social animal which relies on interactions with others and, since their discovery in the early 1990s, many neuroscientists have speculated on the significance of mirror neurons in human evolution.

The mirror neuron system has, in fact, been implicated in empathy and processes which require imitation learning, such as language acquisition. Some neuroscientists also believe that abnormally functioning or non-functioning mirror neurons may be the biological basis of autism.