mirror cells Wallman commentary

mirror cells Wallman commentary - Vol 451|17 January 2008...

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Songbirds are champion mimics. A nighting ale, for example, can imitate at least 60 different songs after a few exposures to each 1 . A young bird learns its species’ song through imita- tion, and the ability is also socially important: a bird on its territory will often respond to an intruder’s song by singing a similar song, thus acknowledging the intrusion 2 . What neurons might mediate these imitative and communi- cative powers? On page 305 of this issue, Prather et al. 3 identify a class of brain neurons that are active both when the bird hears a song and when it replies by singing a similar song. As such, these neurons are reminiscent of the mirror neurons discovered in the monkey brain. These respond similarly whether an action is perceived or performed, and they aroused enormous interest as a pos- sible key to understanding such disparate phenomena as imitation and empathy. Mirror neurons are activated both when a monkey performs a discrete action — such as grasp- ing a small object between thumb and fore- finger — and when it sees another monkey or a human do the same 4 , but not when the same action is performed without accomplishing the goal (pretending to grasp the object). To mirror neurons, actions performed or observed are equivalent, so they could medi- ate imitation — a most mysterious form of learning. How does one know what pattern of muscle contraction corresponds to a par- ticular visual effect? The psychologist William James speculated that infants correlate their random limb movements with the sight of their limbs, thereby forming an association between motor outputs and visual inputs that allows them to infer how others make similar limb movements. But one does not need to spend hours in front of a mirror to imitate the facial expressions of others 5 ; nor do French or Italian children need to observe themselves to acquire the facial gestures characteristic of their elders. Mirror neurons may be the link between the sensory information perceived and gestures produced. Mirror neurons might also facilitate our perception and memory of complex sensory stimuli 6 . For example, a sequence of familiar dance steps could be more easily encoded in memory in terms of the commands that the brain sends to move the limbs than it could by remembering all the small visual changes these limb movements produce. This function of mirror neurons would not be independent of their ability to facilitate imitation. Indeed, it is a common experience, when watching a car chase in a film, to feel oneself invol- untarily making small steering or braking movements. The responses of mirror neurons have led psychologists to propose that they provide a way of inferring the workings of another’s mind, and so are essential for the develop- ment of social communication and empathy 7 . This has put the emphasis on mirror neurons’
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mirror cells Wallman commentary - Vol 451|17 January 2008...

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