Mirror Neurons
May 6, 2007 — filipefernandesVideo from PBS: Nova : http://www.pbs.org/wgbh/nova/sciencenow/video/3204/i01.html
A mirror neuron is a neuron which fires both when an animal performs an action and when the animal observes the same action performed by another (especially conspecific) animal. Thus, the neuron “mirrors” the behavior of another animal, as though the observer were itself performing the action. These neurons have been directly observed in primates, and are believed to exist in humans and in some birds. In humans, brain activity consistent with mirror neurons has been found in the premotor cortex and the inferior parietal cortex. Some scientists consider mirror neurons one of the most important findings of neuroscience in the last decade. See for example this[ http://www.edge.org/3rd_culture/ramachandran/ramachandran_p1.html ] essay by Ramachandran on their potential importance in imitation and language acquisition.
Possible functions of the mirror neuron system
Many different functions for the mirror neuron system have been suggested. These include:
Understanding Intentions
Many studies link mirror neurons to understanding goals and intentions. Fogassi et al. (2005) recorded the activity of 41 mirror neurons in the inferior parietal lobe (IPL) of two rhesus macaques. The IPL has long been recognized as an association cortex that integrates sensory information. The monkeys watched an experimenter either grasp an apple and bring it to his mouth or grasp an object and place it in a cup. In total, 15 mirror neurons fired vigorously when the monkey observed the “grasp-to-eat” motion, but registered no activity while exposed to the “grasp-to-place” condition. For four other mirror neurons, the reverse held true: they activated in response to the experimenter eventually placing the apple in the cup but not to eating it. Only the type of action, and not the kinematic force with which models manipulated objects, determined neuron activity. Significantly, neurons fired before the monkey observed the human model starting the second motor act (bringing the object to the mouth or placing it in a cup). Therefore, IPL neurons “code the same act (grasping) in a different way according to the final goal of the action in which the act is embedded” (664). They may furnish a neural basis for predicting another individual’s subsequent actions and inferring intention.
Empathy
Mirror neurons have been linked to empathy, because certain brain regions (in particular the anterior insula and inferior frontal cortex) are active when a person experience an emotion (disgust, happiness, pain etc) and when they see another person experience an emotion. However, these brain regions are not quite the same as the ones which mirror hand actions, and mirror neurons for emotional states or empathy have not yet been described in monkeys. More recently, Keysers and colleagues have shown that people that are more empathic according to self-report questionnaires have stronger activations both in the mirror system for hand actions and the mirror system for emotions providing more direct support to the idea that the mirror system is linked to empathy.
Language In humans
mirror neurons have been found in the inferior frontal cortex, close to Broca’s area, a language region. This has lead to suggestions that human language evolved from a gesture performance/understanding system implemented in mirror neurons. Mirror neurons certainly have the potential to provide a mechanism for action understanding, imitation learning, and the simulation of other people’s behaviour. However, like many theories of language evolution, there is little direct evidence either way.
Autism
Some researchers claim there is a link between mirror neuron deficiency and autism. In typical children, EEG recordings from motor areas are suppressed when the child watches another person move, and this is believed to be an index of mirror neuron activity. However, this suppression is not seen in children with autism. Also, children with autism have less activity in mirror neuron regions of the brain when imitating. Based on these results, some researchers claim that autism is caused by a lack of mirror neurons, leading to disabilities in social skills, imitation, empathy and theory of mind. This is just one of many theories of autism and it has not yet been proven.
Theory of Mind
In Philosophy of mind, mirror neurons have become the primary rallying call of simulation theorists concerning our ‘theory of mind’. ‘Theory of mind’ refers to our everyday ability to predict and explain quite accurately the mental states of others without direct knowledge of them; for example, how you know a friend is in pain when he says “ouch”, or can assume that a person being chased is afraid of the thing after him. According to simulation theory, that knowledge is available because we subconsciously put ourselves in the shoes of the person we’re observing and, accounting for relevant differences, imagine what we would do in that scenario. Mirror neurons have been taken to be the mechanism by which we simulate others in order to better understand them, and therefore their discovery has been taken as a validation of simulation theory (which appeared a decade before the discovery of mirror neurons).
Gender differences
Stronger EEG responses related to the mirror neuron system have been recorded in women compared to men. This finding is consistent with the idea that women tend to be more empathetic, that the mirror neuron system is related to empathy, and that weak responses in the mirror neuron system could be linked to a masculine mind and to autism. However, these ideas have not been tested in full.
Excerpt from Wikipedia, full text and references: http://en.wikipedia.org/wiki/Mirror_neurons
In an article published in February in Nature, a group of researchers presents a study where it is shown that lesions of a certain part of the brain, the ventromedial prefrontal cortex, alters the normal judgements of right and wrong for a selective set of moral dilemmas. Being that this part of the brain is related to emotions, it is apparent that emotions and moral judgement are related.
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