Researchers understanding of the functions of mirror neurons remains the subject of much debate. A myriad of possible functions have been suggested, including an explanation for the common coding theory (perception-action coupling), understanding and predicting the actions and intentions of others, learning new skills through imitation, theory of mind, language acquisition, and empathy (Fogassi, Ferrari, Gesierich, Rozzi, Chersi & Rizzolatti, 2005; Gallese & Goldman, 1998; Skoyles, 2010; Keysers, 2011). Researchers have also implicated mirror neurons as a possible underlying mechanism for a variety of psychological and cognitive disorders including Schizophrenia and Autism (Oberman, Hubbard, McCleery, Altschuler, Ramachandran & Pineda, 2005). While the scientific community’s interest in mirror neurons is already readily apparent, the necessity for further research in both animal and human models to elucidate their possible functions and development remains.
Discovery of Mirror Neurons
Mirror neurons were first described in the early 1990’s by a group of neurophyisists working at the University of Parma, in Parma, Italy. Their discovery, like many scientific findings, was serendipitous, uncovered accidently in the midst of research designed to explore the functions of “canonical neurons” in Rhesus Macaque monkeys (Rizzolatti & Fabbri-Destro, 2010). Giacomo Rizzolatti, Giueppe Di Pellegrino, Luciano Fadia, Leonardo Fosgassi and Vittorio Gallese were conducting research exploring neuron functioning and mouth movements in Macaques using single neuron recordings in the F5 region of the ventral premotor cortex (Pellegrino, Fadiga, Fogassi, Gallese & Rizzolatti, 1992). It was during their recording of hand and arm movements (e.g. grasping objects) in the Macaques when they discovered that certain F5 neurons are active when conducting motor movements and when observing some experimenter’s motor actions, even without any discernible movement of the Macaque (Pellegrino et al., 1992). Pellegrino and his colleagues originally submitted a description of their findings to Nature, which rejected their manuscript for a “lack of general interest” (Rizzolatti & Fabbri-Destro, 2010). After the rejection from Nature the manuscript was then published in Experimental Brain Research in 1992, after Rizzolatti shared the research findings with Dr. Otto Creutzfeld, the then Coordinating Editor of the journal (Rizzolatti & Fabbri-Destro, 2010). Since the mirror-neuron system’s (MNS) introduction into the scientific community a host of researchers, philosophers, and lay-persons alike have attributed a variety of cognitive processes, pathologies, and deficits to the their existence or dysfunction.
Mirror neuron research is still in its infancy, leaving a complete understanding of its historical significance yet unrealized. While some question the validity, significance, or human application of research providing support for mirror neurons, (Dinstein, Thomas, Behrmann & Heeger, 2007; Lingnau, Gesierich, & Caramazza, 2009; Churchland, 2011) others have gone as far as to deem them as the “driving force behind the great leap forward in human evolution” (Ramanchandran, 2000). He went on to speculate “that mirror neuron’s will do for psychology what DNA did for biology: they will provide a unifying framework and help explain a host of mental abilities that have hitherto remained mysterious and inaccessible to experiments” (Ramanchandran, 2000). These divergent views on the significance of mirror neurons reflect similar processes undergone by previously proposed learning theories, with proponents and opponents seeking to validate their own conceptualization while discrediting others.
In the learning field, several theories invoke brain mechanisms to explain learning in varying degrees including, Thorndike’s neural bond, Pavlov’s cortical mosaic and Gestalt theory’s principle of isomorphism. However, mirror neurons provide the sole, truly neurophysiological, mechanism for learning, describing both a well-documented learning phenomenon and the neural events that underlie it (Olson & Hergenhalm, 2009). The shift from learning theories such as Pavlovian learning and Gestalt theory, to social-cognitive and Hebbian learning reveals a pattern towards the description of ever increasingly complex learning phenomenon. Additionally, learning theory attributed to mirror neurons relies on the understanding of neural activity, moving away from the inclusion of elements such as cognitions, reinforcement and emotion in the explanation of learning. The relatively recent discovery of mirror neurons and the implication of these neurons in the learning process may indicate another transition in the understanding of how humans and other animals represent intricate social learning at a neural or cellular level. This transition, should future research further elucidate our understanding of how the mirror neuron system works, may represent a conceptual advancement of learning theory which could reshape the fields of neuroscience and psychology, while informing educational policy, medicine, rehabilitation, and psychological treatment.
The first research studies designed to explore and understand the functions of mirror neurons were conducted in the Rhesus Macaque monkey. Mirror neurons in these non-human primates were located in the F5 region of the inferior frontal gyrus and the inferior frontal lobule (Rizzolatti & Craighero, 2004). Early mirror neuron experiments in non-human primates explored their possible functional role in mediating imitation and action understanding. Rizzolatti, Fogassi & Gallese (2001), proposed that mirror neurons mediate understanding the actions done by other through a simple mechanism. Specifically, they argued that when an individual observes another person performing an action, neurons tied that specific action become activated in the observer’s premotor cortex. This motor representation of the observed action corresponds to that which is generated during active action, thus transforming visual information into knowledge.
Traditionally, the most direct and simplest way to prove that the mirror-neurons system is the bases for action understanding is to damage the implicated areas and examine the effects of the lesion in the monkey’s ability to recognize the actions in others. However, Rizzolatti et al. (2001), suggest that this method has inherent limitations including (1), the mirror-neuron system is likely present in both hemispheres and recruits large areas of both the parietal and premotor cortices, (2) there may be additional mechanisms that also facilitate action recognition, and (3) large lesions could result in general cognitive deficits making an accurate interpretation of results difficult. Therefore, researchers designed experiments that assessed mirror neuron activity in circumstances in which the monkey would understand the meaning of a specific action however had no exposure to the visual components that would traditionally actuate mirror neurons.
One investigation conducted by Kohler, Keysers, Umilta, Fogassi, Gallese & Rizzolatti (2002), tested whether F5 mirror neurons would differentiate actions from only their sound. Kohler et al. (2002), recorded F5 mirror neuronal activation as a monkey observed an action coupled with a loud noise (e.g. ripping a piece of paper) or was exposed to the same noise without viewing the action. Their results indicated that approximately 15% of the mirror neurons that responded to the presentation of an action along with a sound, also became active with the sound alone. These neurons, which responded specifically to action sounds, were later coined “audio-visual” mirror neurons. Kohler et al. (2002), also conducted a study in which two loud acts were presented randomly in “vision-and-sound, sound only, and motor” conditions. The monkey performed the actions that they witnessed or heard in the sensory conditions. Twenty-nine of a possible 33 examined neurons displayed auditory discrimination for one of the two actions, and the selectivity in visual and auditory modality corresponded to the preferred motor action.
A second set of investigations conducted by Umilta, Kohler, Gallese, Fogassi, Fadiga, Keysers & Rizzolatti (2001), explored whether mirror neurons would fire if a monkey does not observe an action occurring, but has adequate contextual information to develop a cognitive model of the action. Their experiment was comprised on two conditions: (1) a monkey observed a visible action directed towards an object and (2) the monkey saw the same action, however with the final component hidden from view (Umilta et al., 2001). Additionally, in a second set of conditions, the experimenter conducted an identical, fully visible, mimed action with no target object, and a hidden, mimed action. Their results indicate that more than half of the neurons recorded from were active during the observation of grasping and holding actions and when the stimulus-triggering features were unseen by the monkey. Additionally, mirror neurons did not activate in the mimed condition as expected. Umilta et al. (2001), interpreted their results as support for the role of mirror neurons in the phenomenon of action understanding. Both of these studies indicate that mirror neuron activity is correlated with action understanding, and that the visual elements of an action are important to generate mirror neuron activation as they allow for the comprehension of the observed action.
Due to the difficulty of conducting research designed to study single neurons in humans, the majority of evidence for human mirror neurons has been collected through indirect means. The most commonly used methods for exploring the existence and functions of mirror neurons in humans are through neuropsychological lesions and subsequent deficits, functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) studies.
An article published in Science, by Lacoboni, Woods, Brass, Bekkering, Mazziotta & Rizzolatti (1999), using an fMRI, suggests that a mirror neuron system may be active in the inferior frontal cortex and superior parietal lobe, which active when an individual completes an action and when an individual observes another person performing the same action. Gazzola & Keysers (2009), corroborate these findings, providing evidence that even fMRI data for single participants showed large areas of increased cortical activation both during the execution and observation of actions. Furthermore, neuropsychological correlates have provided evidence through lesion studies examining areas that are associated with action knowledge and understanding, pantomime interpretation and motion perception impairments , which suggests an association between the inferior frontal gyrus and these behaviors (Saygin, Wilson, Dronkers & Bates, 2004; Tranel, Kemmerer, Adolphs, Damasio & Damasio, 2003; Saygin, 2007).
One study reporting single neuron recordings conducted by Mukamel, Ekstrom, Kaplan, Lacoboni & Fried (2010), recorded neuronal activity in 21 patients being treated for epilepsy. These patients were implanted with electrodes to isolate the source of their seizures, which allowed the researchers to explore possible functions of mirror neurons simultaneously. Their results showed that a small number of neurons activated both when the partiticapnt performed a task and when they observed the same task being carried out by another person (Mukamel et al., 2010). Furthermore, they were able to identify neurons that exhibited anti-mirror properties, responding when they saw an action performed and becoming inhibited when performing the same action. This study is one of the few investigations in humans that reports direct support for the presence of a mirror neuron system.
Doubts Concerning Mirror Neurons (Weaknesses)
While multiple sources of evidence for mirror neurons have been documented since Pellegrino and colleagues first described their discovery in 1992, individuals in the scientific community have voiced their doubts regarding the existence of a mirror neuron system and question the methodology used in early mirror neuron research. Dinstein et al. (2008), argue that the qualitative nature of the neurophysiological studies describing the individual cell properties of mirror neurons limits what conclusions can be drawn about a mirror neuron system. Dinstein et al. (2008), contend that because early results and interpretations have been based on responses from only 16-22 neurons that differentiated between only two different movement, further neurophysiological studies are needed to evaluate the functions of these neurons, with “a specific emphasis on establishing a causal connection between mirror neurons and the ability of the animal to understand observed movements”.
The existence of mirror neurons has not come under attack due only to questions regarding research methodology and small sample cell sizes. In his article, “Eight Problems for the Mirror Neuron Theory of Action Understanding in Monkeys and Humans”, Hickok (2009), points to several arguments against mirror neurons. Several of the arguments posited by Hicock reflect the opinions of others in the scientific community. Hickok (2009), notes a lack of research evidence examining pharmacological or lesion related interruptions of motor areas in F5, which would result in decreased motor and action recognition. Hickok (2009), argues that if mirror neurons located in F5 are responsible for understanding and predicting motor actions, then lesions in that area should result in the impairment of action understanding. Hickok (2009), argues that current evidence does not substantiate this prediction. Hicock (2009), also argues that the discovery of “mirror neurons” in the M1 (primary motor cortex) of Rhesus Macaque monkeys undermines a previous assumption made about how mirror neurons are believed to work. Specifically, a previous lack of M1 mirror neurons was interpreted as disconfirming evidence for the potential that the Macaques were generating movement responses during perception action covertly. However, now that mirror neuron characteristics have been described in M1 through TMS studies, Tkach, Reimer & Hasopoulos (2007) argue that “mirror” responses could simply be the “facilitation of the motor system via learned associations”.
Lingnau, Gesierch & Caramazza (2009), published an article refuting the existence of mirror neurons in humans using fMRI data. Lingnau et al. (2009), assert that any study that intends to explore the existence of mirror neurons in humans must fulfill two conditions including; (1) a demonstration that “‘execution and recognition of a specific motor act activates a set of neurons in the so-called mirror neuron areas, and (2) activation of neurons within potential mirror neuron areas results from direct activation and not from a prior non-motor categorization on the basis of inferences about potential motor acts from minimal visual cues”. Lingnau et al. (2009), conducted a study using an fMRI to determine if cortical areas believed to contain mirror neurons would acclimate if an identical motor act were repeated. In their study, they carried out experiments in where they compared actions that were observed first and then subsequently executed, to motor actions that were executed first and observed second. Their results suggested that there was substantial asymmetry between the two methods, which they interpreted as evidence against mirror neurons in humans (Lingnau et al., 2009). They stated:
“Crucially, we found no signs of adaptation for motor acts that were first executed and then observed. Failure to find cross-modal adaptation for executed and observed motor acts are not compatible with the core assumption of mirror neuron theory, which holds that action recognition and understanding are based on motor simulation” (Lingnau et al., 2009).
Some researchers have attempted to explain the development or mirror neurons rather than refute their existence entirely. Heyes (2009), suggests that mirror neurons may be a byproduct of “associative learning, the same kind of learning that produces Pavlonian conditioning”, rather than an evolutionary adaptation for action understanding. The evolutionary adaptation hypothesis of mirror neurons posits that humans and non-human primates are born with mirror neurons, and that experiences play a minor role in their development. Conversely, Heyes’ “Associative Sequence Learning Hypothesis” argues that each mirror neuron is refined through sensorimotor experiences by watching and completing the same behavior. Heyes (2009), suggests that while both hypothesis provide conceivable accounts for the origins of mirror neurons, the “Associative Sequence Learning Hypothesis” has three advantages; (1) it offers a parsimonious, empirically testable account for the differences between humans and primates, (2) it supports evidence which demonstrates that mirror neurons are involved in a variety of social and cognitive functions, however do not have a significant or specialized role in action understanding, and (3) is corroborated by data indicating that even through adulthood, the mirror neuron system can be influenced by sensorimotor learning.
Possible Functions of Mirror Neurons
One possible function often attributed to mirror neurons is understanding and predicting the goals and intentions of others’ actions. Fogassi et al. (2005), recorded activity in forty-one potential mirror neurons located in the inferior partial lobe (IPL), a cortical region recognized as an association cortex that is responsible for the assimilation of sensory and motor information, in Rhesus Macaques. During experimental trials, the Rhesus Macaques observed an experimenter grasp food and bring it to its mouth or grasp a target object and place it in a separate container (Fogassi et al., 2005). The recordings indicated that approximately 15 of these mirror neurons fired when the Rhesus Macaque observed the experimenter grasping the food item to eat, however did not activate when they observed the experimenter grasp the object to be placed in a container. Additionally, several of the recorded mirror neurons activated in a reverse pattern, firing when the experimenter placed and object in a container and not when the food item was grasped to be eaten. These findings are significant because they suggest that the type of action and not simply the movement of the experimenters arm determined how mirror neurons respond. Furthermore, because the neurons would fire before the Rhesus Macaques observed the investigator initiating the second motor act (food to mouth vs. place object in cup), that they “code the same act” (grasping) in a different manner as it relates to the final goal of the behavior. Fogassi et al. (2005), argue that this activity suggests that mirror neurons may be a neural mechanism for the prediction of another person’s actions and inferring their intentions.
Theory of Mind
In a similar vein as understanding the intentions of others, Theory of Mind, which refers to the capacity to infer another individual’s “mental state”, such as beliefs, thoughts and desires from the experiences of their overt behavior. While a number of competing models attempting to account for the capacity for theory of mind in humans have been posited, the most salient in regards to mirror neurons is Simulation theory. Simulation theory (ST) posits “that we represent the mental states and processes of others by mentally simulating them, or generating similar states and processes in ourselves” (Gordon, 1986). Researchers have interpreted mirror neurons as the neural mechanism that allows humans to simulate others behaviors and actions to better understand them (Gallese & Goldman, 1998). While simulation theory predates the discovery of Mirror Neurons, researchers have begun to interpret them as a potential mechanism by which we simulate others to better understand them and subsequently inform our scenario simulations (Gallese & Goldman, 1998).
Several proponents of mirror neuron theories have implicated these neurons in the production, expression and understanding of empathy described as the understanding and vicarious experiencing of the emotions, thoughts and experiences of other (Preston & de Wall, 2002; Decety, 2002: Decety & Jackson, 2004; Gallese & Goldman, 1998; Gallese, 2001; Keysers, 2011). Several experiments using fMRI, EEG and MEG have reported increased brain activation in areas understood to be involved in the experience of emotions (i.e. disgust, happiness, emotional pain, etc.). These brain areas, in particular the insula, anterior cingulated cortex and inferior frontal cortex are active both when people experience emotions, and when they see other’s experiencing an emotion (Keysers, 2001).
Botvinick, Jha, Bylsma, Fabian, Solomon & Prkachin (2004), hypothesized that observing faces expressing pain would elicit activity in neural systems that also activate while experiencing direct pain. While they were not exploring the possibility of mirror neurons specifically, their predictions imply a neural mechanism that activates during both a firsthand experience of pain, and a mirroring effect while observing other in pain. Their results indicated that when participants were subjected to painful thermal stimulation and when they observed others endure painful thermal stimulation, the expected cortical regions were activated. Singer, Seymour, O’Doherty, Kaube, Dolan & Frith (2004), provide corroborative evidence for similar cortical activation during the experience of direct pain and observing others pain using fMRI recordings. Singer et al. (2004), examined cortical activity while participants were subjected to a painful stimulus, and then compared results to when participants observed a light signifying that their loved one was receiving the same painful stimulus. Additionally, activation of specific cortical areas, including the anterior insula and rostral anterior cingulate cortex, was correlated with the participant’s score on an empathy measure, suggesting that individuals who exhibited elevated cortical activation levels in response to direct and observed pain experienced higher levels of empathy. Gazzol, Aziz-Zadeh & Keysers (2006), provide more direct support for a link between empathy and mirror neurons, reporting that individuals that rate themselves higher on empathy measures show stronger activation in the mirror system for hand actions.
Further evidence for an underlying neural mechanism for processing others emotional responses was reported by Wicker, Keysers, Plailly, Royet, Gallese, Rizzolatti (2003). Using fMRI, Wicker et al. (2003), observed participants inhale odorants, which elicited strong feelings of disgust, and watching videos of faces conveying the emotion of disgust. Their results indicated that observing “disgusted” faces and experiencing the feeling of disgust, activated the same areas of the anterior insula and anterior cingulated cortex, both areas commonly associated with the experience and expression of disgust.
The belief that Mirror Neurons are involved in language acquisition stems from a gestural language origins theory, which posits that verbal language evolved from a communication system that used hand gestures. Skoyles (2000), suggests mirror neurons are critical to any theory of gestural communication, arguing that they can explain (a) “how signs could be made that we readily understood, and (b) why verbal language arose from these abilities after early gestural language became extinct”. Skoyles (2000), posits that the motor imitation characteristics of mirror neurons, which activates when an animal performs an action, and when that animal sees the same action being performed, provides a neural mechanism for the acquisition and learning of gesture signs. Additionally, many neuroscience researchers agree that the ventral premotor cortex (F5) region (where mirror neurons have been identified in Rhesus Macaques) is the homolog of Broca’s Areas, believed to be one of the primary language areas in humans (Rizzolatii & Arbib, 1998). In conjunction, these two points provide a means by which hand movements could have taken on the role of gestures, and how mirror neurons could be responsible for Broca’s area turning into a specialized language area (Skoyles, 2000).
While some investigators are still researching the existence and possible functions of mirror neurons in humans, other have begun to discuss how the mirror neuron system, and more specifically its dysfunction, may be related to a variety of psychological and cognitive disorders. The most commonly cited disorders implicating a mirror neuron dysfunction as an underlying neurological mechanism include Autism, Schizophrenia, and Antisocial Personality Disorder. Other researchers suggest that mirror neurons might also be implicated in language deficits, depression, and Asperger’s. Because the scientific community’s understanding of mirror neurons remains in its nebulas stage, and due to methodological restrictions for the continued research of mirror neurons, conclusions about their role in psychological and cognitive disorders is tentative at best.
In 2005 researchers from University of California and Mt. Sinai School of Medicine published a paper providing evidence for mirror neuron dysfunction in Autism Spectrum Disorders (ASD) (Oberman et al., 2005). Oberman et al. (2005), connected 10 children with a diagnosed Autism Spectrum Disorder and 10 matched controls to an electroencephalograph, and recorded brain wave patterns over the sensorimotor cortex, believed to indicate mirror neuron activity, during several experiment tasks. Oberman et al. (2005), argue that because brain wave activity in these areas are suppressed when typically developing individual both perform and observe a specific action, that a lack of suppression may suggest dysfunction in the mirror neuron system. Their results indicated that controls showed substantial suppression responses while performing and observing a task, while participants with ASD only showed suppression when performing a task. The investigators hypothesize that this lack of suppression supports the notion of a dysfunctional mirror neuron system. Conversely, several researchers argue against the “broken Mirror Neuron” explanation for autism, suggesting that it is too simplistic and that indirect measures such as fMRI and EEG do not necessarily represent mirror neuron functioning (Dinstien et al, 2009).
Some researcher point to Theory of Mind as a mediator between mirror neuron dysfunction and psychological disorders such as Schizophrenia. Frith (1994), suggests that defective Theory of Mind abilities lead to disorders of “willed action, self-monitoring, and monitoring of others” in Schizophrenia. He asserts that failure to recruit mirror neuron systems may lead to a failure in self-monitoring and the production of positive symptoms such as hallucinations and delusions. Neuroimaging research corroborates this view, finding that brain areas currently understood to be involved in Theory of Mind often function abnormally in individuals with Schizophrenia (Ang & Pridmore, 2009).
The application of Mirror Neurons to the Industrial/Organizational Psychology field are all but nonexistent in the literature. Predicated on the assumption that Mirror Neurons are involved in phenomenon such as understanding intentions, motor mimicry, empathy, Theory of Mind, and observational learning at a neural level, several I/O applications can be inferred. For example, an understanding of Mirror Neurons may provide a basis for the development and implementation of on the job training modules designed to have trainees observe job specific tasks by supervisors or exemplars. If mirror neurons are involved in motor mimicry and learning specific motor tasks, than observing models perform work tasks may provide additional benefits to speed of task learning and efficiency. Additionally, mirror neuron theory may inform ways to establish empathy and theory of mind training in work environments to foster a caring and supportive work culture. Establishing supportive work environments and promoting empathy may increase productivity and efficiency in employees and may reduce work related confrontation. Specifically, providing empathy training to supervisors and managers may help reduce workplace stress and authority resistance by fostering more caring and genuine relationships between management and employees.