Mirror Neurons: Fact and Hype

Neurons that fire both when a monkey acts and when it watches someone else act: a fascinating discovery from Parma, the grand claims made for it — empathy, language, autism — and what the evidence supports.

The discovery

In the early 1990s, Giacomo Rizzolatti and colleagues at the University of Parma were recording from neurons in a premotor area of the macaque monkey brain (area F5) that fired when the monkey grasped objects. They noticed that some of these neurons also fired when the monkey simply watched an experimenter grasp an object. They called them mirror neurons, and published key reports in 1992 and 1996. Similar cells were later found in the monkey parietal lobe.

The big claims

The discovery was quickly linked to grand ideas. Mirror neurons were proposed as the basis of understanding others' actions, of imitation, of empathy, of the evolution of language (area F5 is considered a possible counterpart of Broca's area) — and their dysfunction as a cause of autism (the "broken mirror" hypothesis). One prominent neuroscientist predicted mirror neurons would do for psychology what DNA did for biology.

The pushback

Critics, notably Gregory Hickok in The Myth of Mirror Neurons (2014), argued that the claims outran the data. People with damage to motor regions can still understand actions they cannot perform; monkeys, which clearly have mirror neurons, don't imitate well or have language; and evidence for a broken mirror system in autism has been inconsistent. Mirror-like activity might reflect associative learning — linking seeing and doing — rather than a dedicated system for understanding minds.

What's solid

Neurons with mirror properties exist in monkeys. In humans, most evidence comes from brain imaging showing overlapping activity for doing and observing actions; a 2010 study by Roy Mukamel and colleagues recorded single neurons in epilepsy patients and found some with mirror-like responses. Most researchers accept that motor systems help process others' actions — the debate is about how much they explain, especially for empathy and social understanding.