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Mirroring Minds

Publié le 1 juillet, 2008 | Pas de commentaires

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Social interaction depends on the ability to recognize the beliefs, knowledge and experiences that determine the actions of others. How we gather this abstract information was largely unknown before the last decade,when researchers discovered mirror neurons in the monkey brain. In the decade following this discovery, these neurons have been implicated in a host of human behaviours from imitative learning to empathy.

ogglog, Brainbow, 2007
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The idea that humans can relate to what others are experiencing is nothing new. Adam Smith described this notion over a century ago: “The mob, when they are gazing at a dancer on the slack rope, naturally writhe and twist and balance their own bodies, as they see him do.1” To the observers on the ground, watching a tightrope walker’s perilous traverse is more than just a passive affair. They can be seen to mimic the erratic movements, despite the fact both feet are planted firmly on the ground. Even autonomic functions are affected, with increased heart rate and sweaty palms a likely characteristic of many audience members. Such a reflexive response, however, does not occur when one watches inanimate objects or other species. The sight of a Bald Eagle perched atop a wavering spruce is not likely to instill the same fear and anxiety that is experienced while watching the tightrope walker.

A natural awareness of the experience of others is critical for the social interaction exhibited by the human species, and is arguably one of the fundamental characteristics that distinguishes us from animals. And yet, until recently, its biological basis has remained poorly understood. Social scientists had long acknowledged the categorical difference between our perception of the inanimate world and our perception of others 2. On the other hand, cognitive neuroscience largely ignored this qualitative difference, focusing rather on how stimuli is integrated and organized within the individual mind. The chasm between the fields of neuroscience and social science led to a multitude of theories, each attempting to explain the social perception of humans.

Trends changed in the mid 1990s following the discovery of a population of neurons in the premotor cortex—an area involved in movement planning and coordination—of Macaque monkeys that fired, not only when the animal performed a specific action, like reaching for a banana, but also when the animal observed this action performed by another monkey, or even a participating researcher 3. Scientists have named these nerve cells “mirror neurons” and have suggested that they are involved in assigning meaning to an observed action. Although this may seem like a relatively benign observation, these simian mirror neurons are thought to represent a primitive version of the human mirror neuron system. While experiments testing mirror neurons in humans is ethically unfeasible, indirect studies such as brain imaging and behavioural analysis, strongly support the existence of a similar system in humans. Recent evidence suggests that in humans, mirror neurons have evolved beyond serving to understand basic movement and have acquired the ability to relate meaning to abstract representations, providing tools required for basic social interaction.

Imitative learning

The finding that mirror neurons are activated during both observation and execution of an action suggests that humans understand others by mentally reconstructing observed experiences in their own minds. A logical corollary of this mental mimicry is the ability to integrate an observed action into our own behavioural repertoire—referred to as imitative learning. Contrary to popular thought, learning through imitation is a phenomenon that developed relatively late along the evolutionary scale, and is generally regarded as limited to some primate species, humans in particular 4. It is far more efficient than the more rudimentary trial-and-error learning, and is likely central to the development and dissemination of skills fundamental to human evolution, such as tool manipulation.The existence of a mirror neuron system, which provides a direct link between ‘watching and doing’, has been postulated to be at the basis of this improved imitative learning. Even culture, which can be viewed as an imitation of norms, values and behaviour within a society, is linked to imitative learning, and therefore possibly to a mirror neuron system 5.

Language and Empathy

The motor theory of language evolution argues that the roots of human communication began as a collection of commonly accepted gestures 6. However, until recently there lacked a sound scientific theory that could explain the evolutionary chasm separating the primitive gestural patterns from modern language that uses abstract sounds to communicate simple needs as well as complex ideas. The observation that mirror neurons are similarly activated during both speech and gestural movements suggest these neurons may represent the evolutionary bridge between these two communication patterns (7). The role of mirror neurons in language is further supported by the observation that passively listening to someone speak activates specific neurons in the motor areas responsible for mouth movement 7.

Understanding language, however, involves more than an objective assessment of sounds and symbols. The complete meaning and value of a poem, for example, cannot be completely understood by a paraphrase of its words, but also involves the emotions it inspires in its readers. This ability to sense and understand the emotional undertones is important not only for appreciating fine poetry, but is a fundamental tool required for effective social interaction. Theories on how humans perceive the emotional state of others had remained purely in the fields of social psychology until the discovery of mirror neurons. The fact that these neurons simulate observed actions of others implies that we make assumptions regarding the emotional states accompanying an observed behavior by ‘stepping into the mental shoes’ of another person 8. More commonly referred to as empathy, evidence has been mounting to further support the role of mirror neurons in this ability.

Similar to language processing where listening to sounds activates mouth motor areas, watching the facial expression of others activates brain regions involved in making that same face 9. Although this activation is not overtly executed as a perceived action, minute changes in behaviour have been observed that are thought to reflect this internal mimicry. For example, a plethora of behavioural studies have found that posture, facial expressions and even tone of voice are subtly modified by the speaker depending on who they are interacting with. This imitation is enhanced if the speaker identifies with the listener, suggesting a thorough understanding of the meaning and intentions of an action is imperative for this emotional mimicry 10. Further, when subjects are inhibited from subtly mimicking facial expressions (by being told to hold a pen between their lips), they are less accurate at reading the emotions of others, suggesting that internal emotional mimicry (represented by subtle changes in facial expression) is required to accurately understand the feelings of others 11.

The idea that a solid neural substrate correlates with empathy raises a number of intriguing ideas regarding the basis of human nature. Are there differences in the mirror neuron system between individuals? And if so, how does this manifest itself into behavioural differences. A number of studies investigating children with autism have found important deficits in their mirror neuron system, which could potentially explain their difficulties in understanding and relating to others 7. Furthermore, would individuals with psychopathic tendencies, many of whom seemingly lack empathy, also reveal deficits in their mirror neuron system? While these questions and many others remain to be adequately addressed scientifically, they highlight an interesting link between neurobiology and the enigmas of human behavior.


Scientists have postulated that mirror neurons may have developed in primates as a simple cluster of cells in the premotor cortex responsible for assigning meaning to an observed grasping of an object. Following a tortuous evolutionary journey these neurons developed in humans as a complex network able to understand abstract concepts, such as the communicative and emotional intentions of others, providing the framework necessary for social interaction. Historically, this ability to interact with and understand others has been studied in isolation within various fields ranging from linguistics to behavioural psychology, and each field has proposed their own theories and hypotheses relating to specific aspects of how humans interact with one another. The novelty of the mirror neuron system is that it represents the first neural substrate fundamental to human social interaction, and provides a single theory explaining this human behaviour. Future research into mirror neurons will likely see a union of these disparate fields, hopefully leading to a more global understanding of human social behaviour.


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