Mirrors In The Mind

In three new independent studies, researchers have deepened our understanding of the remarkable ability of some specialized areas of the brain to activate both in response to one’s own actions and in response to sensory cues (such as sight) of the same actions perpetrated by another individual.

This ability is thought to be based in the activity of so-called mirror neurons, which have been hypothesized to contribute to skills such as empathy, socialized behavior, and language acquisition. The new findings contribute to our understanding of how conceptually related instances of language and action, and sound and action, are linked in the brain, and how the brain distinguishes actions perpetrated by “self” and by “other.”

The studies are reported by three independent research groups: Lisa Aziz-Zadeh (now at USC) and colleagues at the University of Parma, Italy, UCLA; Christian Keysers and colleagues at the University of Groningen, The Netherlands and UC Berkeley; and Simone Schütz-Bosbach and colleagues at University College London, the Max Planck Institute for Human Cognitive and Brain Sciences in Germany, and the University of Rome. The papers appear in the September 19th issue of Current Biology, published by Cell Press.

Mirror neurons were first identified in the cortex of macaque monkeys: A particular subset of these neurons fire when, for example, a monkey picks up a banana, and when the monkey observes a human picking up a banana in a similar way. Mirror-neuron activity appears to be highly specific, such that a somewhat different set of mirror neurons would fire if a banana were poked, for example, rather than picked up. There is also evidence that mirror neurons link actions not only with visual stimuli, but also with other types of sensory cues. Technical limitations have impeded identification of individual mirror neurons in humans, but brain-imaging studies support the existence of these neurons.
In the new work from Lisa Aziz-Zadeh and colleagues, researchers used a brain-imaging technique to investigate how literal phrases describing actions performed by the mouth, hand, or foot influenced cortical neurons that are activated by the sight of actions being performed by mouth, hand, or foot.

The researchers found a significant concordance between activation of certain cortical areas in response to linguistic descriptions and observed actions relating to the different body parts carrying out the actions. For example, when individuals read literal phrases such as “biting the peach” or “biting the banana,” some brain areas activated that were also stimulated by videos of fruit being bitten. Similar findings were obtained for hand actions (for example, grasping a pen) and foot actions (for example, pressing a piano pedal). Together, the findings suggest that mirror neurons play a key role in the mental “re-enactment” of actions when linguistic descriptions of those actions are conceptually processed.

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