The sight of a stranger’s foot getting hammered induces an instant surge of sympathy within us. Watching a friend nauseate after eating something repulsive quickly causes our own stomachs to turn. This ability to understand and relate to another individual’s internal state has provided great motivation for research. One source of explanation arose from research on mirror neurons-which fire both during execution and observation of a behaviour (Rizzollati & Arbib, 1998). This particular class of neurons plays a crucial function in human social interactions. The importance of the mirror neuron system (MNS) for communication can be understood through its influence on nonverbal communication including facial expressions and hand gestures and verbal language. Furthermore, disorders affecting human communication-such as autism and schizophrenia-convey the impression of stemming from a malfunctioning MNS.
Generally, human social interaction involves both verbal and nonverbal forms of communication. Obvious examples of nonverbal communication are facial expressions and hand gestures. A recent functional magnetic resonance imaging (fMRI) study by Montgomery and Haxby (2008) found evidence supporting the claim that the MNS contains distinct representations for facial expressions and hand gestures. Particularly, this study examined the inferior parietal lobule and the frontal operculum as the potential MNS brain regions involved in nonverbal communication. Further evidence comes from another fMRI study by Montgomery, Isenberg and Haxby (2007)-which demonstrated the activation of the MNS during hand movements used to manipulate objects and hand gestures used to communicate.
A third fMRI study by Van, Minderaa and Keysers (2007) highlighted similar results by examining other putative MNS brain regions-inferior frontal gyrus, posterior parietal cortex, insula and amygdala-thought to be associated with facial expressions. Activity spontaneously increased in the MNS of participants that produced and observed certain facial expressions (Van et al., 2007). A study by Enticott, Johnston, Herring, Hoy, and Fitzgerald (2008) demonstrated an associations between mirror neurons and facial emotion processing. Instead of using fMRI as a method of analysis, Enticott and colleagues (2008) used the transcranial magnetic stimulation (TMS) technique. In brief, much evidence supporting the involvement of the MNS in the processes of facial expression and hand gesture exists. Such forms of communication form the basis for the later, more complex, verbal language development.
Taking this thought further, verbal language also seems to be linked to the MNS. Firstly, Rizzollati et al. (1998) marked the discovery of mirror neurons in the F5 area within the monkeys’ frontal cortex. This primate-specific F5 area has been considered to be the homolog of the human Broca’s area, which is a region crucial for language (Rizzollati et al., 1998). With this in mind, Horwitz et al. (2003) demonstrated that both spoken and signed language are associated with mirror neurons firing in Broca’s area as a result of the production of language. In addition, an fMRI study by Aziz-Zadeh, Wilson, Rizzollati, and Lacoboni (2006) made evident that the MNS of the premotor cortex is activated both when participants observed mouth, hand and foot movements and when participants read phrases related to these body parts. Overall, these findings suggest that indeed the MNS influences verbal language.
Moreover, another way of understanding the importance of the mirror neurons’ influence on human social interaction is by considering the consequences of a malfunctioning system. Autism spectrum disorder is characterized by social and language impairments. In other words, individuals with autism tend to be less interactive when it comes to communicating with others. Part of the MNS-the posterior inferior frontal and rostral inferior parietal areas are affiliated with social behaviour and imitative learning; however these areas have deficits in autistic individuals (Locoboni & Mazziotta, 2007). In one study individuals with autism spectrum disorder showed significantly different electroencephalography (EEG) recordings of mirror neurons compared to a control group consisting of healthy individuals (Oberman, Hubbard, McCleery, Altschular, Ramachandran, & Pineda, 2005).
Similarly, schizophrenia is another disorder characterized by deficits in social communication, especially of the nonverbal type. Research by Kato Y., Muramatsu, Kato M., Shibukawa, Shintani, and Mimura (2011) using magnetoencephalography recordings on the right inferior parietal cortex showed atypical mirror neuron activity in non-treated schizophrenia patients. Likewise, similar results were found in a study that tested mirror neuron activity using TMS,; it was demonstrated that during action observation a reduction in motor facilitation occurs in schizophrenia patients (Enticott, Hoy, Herring, Johnston, Daskalakis, & Fitgerald, 2008). Clearly, communication impairments observed in individuals with autism and schizophrenia are influenced by the MNS.
In conclusion, human social interaction is influenced by mirror neurons. Evidence supports this statement through research done on the involvement of the MNS in nonverbal communication, including facial expressions and hand gestures and verbal language. Research has also suggested that an impaired MNS negatively affects social interaction, which is exemplified in the cases of autism and schizophrenia.
Taken as a whole, combining mirror neurons’ role in imitative behaviour and social interaction-the process through which humans possibly acquire new social knowledge becomes evident. Additionally, the presence of mirror neurons in primates as well as humans provide evidence for the development of social interaction over the course of evolution. Thus, in order to further strengthen their existing relationship, future research should examine the co-evolution of mirror neurons and social interaction.