CORE CONCEPTS CORE CONCEPTS Mirror neurons

Jessica Marshall Science Writer

Just over 20 years ago, an Italian team re- authorsofthepaperthatfirstreportedthe ported findings on macaques showing the neurons’ existence (1), but he believes it is existence of a “surprising new class” of neu- only for lack of looking. rons in a particular region of the premotor Although there may be little doubt that cortex of the macaque brain (1). These neu- these neurons exist, researchers differ con- rons were active not only when the ma- siderably in their interpretation of what they caque performed an action—like grabbing an do (6). Some say that the neurons are neces- object—but also when the macaque watched sary to understand the meaning of others’ thesameactionbeingperformedbyaperson behaviors. Others believe that they instead or another monkey. The researchers named play a more straightforward role, helping us these neurons “mirror neurons” and pro- to learn motor tasks or to choose our own posed that they provide the basis for what actions, or that we use mirror neurons to help became known as “action understanding” in predict the actions we are observing, without macaques, allowing them to interpret the assigning a goal to them. For example, when intentions or goals of the person or monkey others’ actions don’t jibe with what we expect, whose actions they are observing. we take particular notice and engage other The findings launched a new field of study areas to try to explain them. An example of a . Image within . Researchers were quick to Nobody disagrees that our brains have a courtesy of Richard Cole, Wadsworth look for mirror neurons in humans. The direct, way of simulating what others are doing or Center, New York State Department of ’ invasive methods used to observe them in predicting others actions and intentions, says Health, Advanced Light Microscopy and macaques cannot be used for studying the James Kilner of University College London. Image Analysis Core. human brain, but other evidence supports their The question is, how much of this ability is existence. “Although the function of mirror embodied in mirror neurons in the motor neurons is highly debatable, I would be very system versus in other areas of the brain? If neurons play a role in disorders like autism surprised if something like mirror neurons indeed mirror neurons are important for un- and schizophrenia. If autism, one hallmark of didn’texistinhumans,” says Greg Hickok derstanding others’ behavior, that raises the which is a difficulty in relating to others, is of the University of California, Irvine. Indeed, question of whether people with motor prob- related to malfunctioning mirror neurons in researchers have since published papers argu- lems therefore interpret the social world dif- the motor system that lead to impairments in ing that mirror-like systems in humans un- ferently,orevenwhetherthereisabasisinthe understanding the meanings of others’ ac- derlie experiences from speech to emotions to motor system for social disorders, Kilner says. tions, then perhaps motor therapies could pain to music (2–5). For example, the same Indeed, one area of great interest—and of be helpful in improving the social skills of brain regions that fired when people smelled additional controversy—is whether mirror individuals on the autism spectrum (7). something disgusting also were active when people saw someone else making a disgusted face (3). The implication of this system is that, 1 di Pellegrino G, Fadiga L, Fogassi L, Gallese V, Rizzolatti G (1992) 4 Singer T, et al. (2004) for pain involves the affective but Understanding motor events: A neurophysiological study. Exp Brain not sensory components of pain. Science 303(5661):1157–1162. cognitively speaking, we are putting ourselves Res 91(1):176–180. 5 Molnar-Szakacs I, Overy K (2006) Music and mirror neurons: From in another’s shoes as we observe an action. 2 Watkins KE, Strafella AP, Paus T (2003) Seeing and hearing speech motion to ‘e’motion. Soc Cogn Affect Neurosci 1(3):235–241. The only other animal besides macaques excites the motor system involved in speech production. 6 Gallese V, et al. (2011) Mirror neuron forum. Perspect Psychol Sci and humans where mirror neurons have been Neuropsychologia 41(8):989–994. 6(4):369–407. 3 Wicker B, et al. (2003) Both of us disgusted in My insula: The 7 Cattaneo L, et al. (2007) Impairment of actions chains in autism found is in songbirds, says Vittorio Gallese of common neural basis of seeing and feeling disgust. Neuron 40(3): and its possible role in intention understanding. Proc Natl Acad the , , one of the 655–664. Sci USA 104(45):17825–17830.

www.pnas.org/cgi/doi/10.1073/pnas.1404652111 PNAS | May 6, 2014 | vol. 111 | no. 18 | 6531 Downloaded by guest on September 29, 2021