The mirror neuron system

• Researchers came across mirror neurons quite by accident. Rizzolatti et al. were studying electrical activity in a monkey’s motor cortex (part of the brain controlling movement) when one of the researchers reached for his lunch in view of the monkey. The monkey’s motor cortex became activated in exactly the same way as it did when the animal itself reached for food.
• Gallese and Goldman suggested that mirror neurons respond not just to observed actions but to intentions behind behaviour. Rather than the common-sense view that we interpret people’s actions with reference to our memory, Gallese and Goldman suggested that we simulate others’ actions in our motor system and experience their intentions using our mirror neurons.
• It has also been suggested that mirror neurons are important in other social-cognitive functions, for example, ToM and perspective-taking. If mirror neurons fire in response to others’ actions and intentions this may give us a neural mechanism for experiencing, and hence understanding, other people’s perspectives and emotional states. Just as we can simulate intention by making judgements based on our own reflected motor responses, this same information may allow us to interpret what others are thinking and feeling.
• Ramachandran suggested mirror neurons are so important that they have effectively shaped human evolution. The uniquely complex social interactions we have as humans require a brain system that facilitates an understanding of intention, emotion and perspective. Without these cognitive abilities we could not live in the large groups with the complex social roles and rules that characterise human culture. Ramachandran suggests that mirror neurons are absolutely key to understanding the way humans have developed as a social species.
• A major source of evidence concerning mirror neurons and perspective-taking comes from the study of mirror neurons in autistic children. If autistic children can be shown to have a dysfunctional mirror neuron system then this may go a long way to explaining autism.
• Ramachandran and Oberman have proposed the ‘broken mirror’ theory of autism. This is the idea that neurological deficits that include dysfunction in the mirror neuron system prevent a developing child imitating and understanding social behaviour in others. This manifestation itself in infancy when children later diagnosed as autistic typically mimic adult behaviour less than others. Later, problems with the mirror neuron system lead to challenges in social communication as children do not fully develop the usual abilities to read intention and emotion in others.
• There is evidence from neuroscience for the role of mirror neurons in a range of human behaviours. Haker et al. scanned the brains of people as they watched a film of people yawning. Levels of activity in the Brodmann’s Area 9, believed to be rich in mirror neurons, increased when participants yawned in response. Contagious yawning is widely believed to be the result of empathy, so this study links mirror neuron activity to empathy.
• Another study by Iacoboni et al. showed that activity in the inferior frontal gyrus (also rich in mirror neurons) increased significantly when the participants tried to understand the intentions behind a hand-grasping gesture (picking up a cup). In other words, mirror neurons encoded why an object was being grasped. This means that mirror neurons may play a role in important aspects of social cognition, including empathy and understanding intentions.
• A limitation of mirror neuron research is measuring neuron activity. Animal studies of mirror neurons often involve implanting electrodes in the brain in order to study electrical activity in individual neurons. However, it is ethically impossible to use this procedure in humans and such animal studies tell us little about human cognition. An alternative is scanning methods, however, scanning techniques only measure activity in brain areas not individual cells. Therefore there is no direct evidence for mirror neuron activity in humans.
• A strength of mirror neuron research is support for explaining autism. Brain scans have shown a smaller average thickness of the pars opercularis in autistic people. This is an area thought to be especially rich in mirror neurons and thought to be involved in perspective-taking. Other studies using scanning methods that show activity rather than just structure, have found lower activity levels in regions of the brain believed to be associated with high concentrations of mirror neurons, again in autistic people. This suggests a cause of autism may be related to the mirror neuron system.
• Although some research has supported a link between autism and abnormal structure or function in the mirror neuron system, a systematic review of 25 studies by Hamilton concluded that evidence was highly inconsistent and results were hard to interpret. This means there may not be a link between autism and mirror neuron activity after all.