VANCOUVER: The debate surrounding the development of mirror neuron systems was revived yesterday when an article was published countering the popular theory that mirror neurons, associated with human cognitive development, evolve through individual experience and are not an innately inherited set of mature traits.
The opinion piece by Richard Cook of City University London appeared in Biology Letters. It cites recent research conducted on macaque monkeys that evaluated ‘tool-use’ and ‘audiovisual’ mirror neuron activity to conclude that the term ‘mirror neuron’ is a serious misnomer.
Less than a third of the neurons studied in the monkeys actually ‘mirrored’ observed behaviour. The research discredits the popular theory that we are born with a set of mature mirror neurons that have been honed into their present form by our ancestors when the properties aided their survival.
Mirror neurons play role in human development
This dominant theory of an inherited behaviour set, accepted at present by a number of cognitive neuroscientists and psychologists, purports that the mirror neuron system provides the physiological mechanisms needed for fundamental sensorimotor behaviour.
Said Cook, “The conceptualisation of mirror neurons as hardwired links between the descriptions of observed actions and the ‘motor programs’ required to produce those actions, made them very useful for theorising.”
This same theory also controversially credits the mirror neuron system with contributing to our understanding of the actions of others, the learning of new skills by imitating, and empathy.
The role of mirror neurons may have been greatly exaggerated
In its most hypothetical form, the mirror neuron system was described as one prominent neuroscientist as ‘the driving force behind the great leap forward in human evolution’, playing a role in language abilities, and in a malfunctioning form, as an underlying factor in cognitive disorders, such as autism.
“Many authors used mirror neurons to explain how our brains solve certain problems, like how we understand and predict the actions of others. However, that these links are frequently imperfect, non-matching and seemingly acquired through experience, poses a challenge for psychologists and neuroscientists seeking to understand how mirror neurons contribute to human cognition”, said Cook.
“In many cases, the mirror neurons that typically emerge through day-to-day experience may be incapable of mediating the putative functions ascribed to them.” According to the research cited by Cook, the role of mirror neurons may have been greatly exaggerated.
Studying single neuron function in the human brain is an inexact science, so the majority of hypotheses have been concluded utilising indirect data. The majority of experiments are conducted on monkeys; animals with fronto-parietal circuits similar to humans.
Raw data shown in monkey trials is extended, albeit theoretically, to human mirror neuron systems. Ascribing the mirror neurons behavioural traits when their very existence and role in humans is still subject to argument complicates the competing theories further.
Cook supports the research collected by Cecilia Heyes of the University of Oxford, who rejects the ‘driving force’ theory of mirror neuron systems. Her data suggests that the individual’s mirror neuron system is “acquired during the course of an individual’s lifetime as a product of correlated experience of observing and promoting actions.”
The ‘tool-use’ mirror neurons in monkeys could be seen firing both when they observed an action being performed with tools and when they performed the action independently. ‘Audiovisual’ mirror neurons were also activated when a sound such as metal striking metal was heard, observed, or performed.
Are mirror neurons hardwired?
“Because the monkeys’ ancestors could not have been exposed to these sights and sounds, these reports argue against the view that mirror neurons are hardwired; that evolution has put them there because they helped our ancestors survive. It appears that the properties of mirror neurons are determined by experience.”
Naznin Virji-Babul of the Univerity of British Columbia recently published findings in Brain and Behaviour that sought to ascertain which of the two competing hypotheses could be observed in human infants. Citing the ongoing research, she said, “The origin of the sensorimotor mirror neuron system, whether it is innate or acquired through experience, is one of the most important problems in neuroscience.
“Both perspectives need to be considered”
“Cook’s discussion of the topic is both timely and important …[and his] hypothesis that the mirror neuron system develops in response to experience is intriguing. I am particularly interested to determine whether this hypothesis is compatible with new results.”
Virij-Babul’s recent research suggests that, at face value, “there may be a basic mirror neuron system optimised to detect coherent motion that is already present in newborns and young infants. That these studies also show previous movement experiences enhance the basic system suggests that both perspectives need to be considered.”
That an unarticulated, underdeveloped mirror neuron system is present in infants in order to better arm them for survival is sure to ensure that the debate will continue for some time. Cook’s support of Heyes’ theory, disputing the presence of a mature system in place from birth, resonates with Virij-Babul’s assertion that both perspectives remain relevant, with Cook concluding that “natural selection may have refined our capacity for associative learning – our ability to connect or link–up events that reliably co-occur – rather than endow us with a mirror neuron system.”
The opinion article in Biology Letters
Virij-Babul’s paper, publishing in Brain and Behaviour