Mirror neurons (MN) have become the well-known topic of discussion in psychology and biology in the past 20 years. After first experiments where Giacomo Rizzolatti et al. (1996) recognized the unknown action in the brain neurons during their experiments with macaque monkeys, biology and psychology gained new theories to develop. The scientists highlighted neuron action when other people were holding food or when other monkeys were holding food. But the first experiments failed because of the lack of evidence (Rizzolatti & Fabbri-Destro 2010). A couple of years later, this topic got its audience. Scientists recognized abnormal neuron movements in the ventral premotor cortex when they tested the macaque’s responses to different arm’s and mouth’s actions (Ferrari et al. 2003). After that the theory found confirmation from other scientists that conducted their experiments. Cristian Keysers (2011) also proved that MN appear when the sound of action occurs. The whole subject mostly represents mirror systems (MS) of monkeys, birds, and humans (Rizzolatti & Fadiga 1999). However, birds have only a sign of the MS. On the other hand, humans and monkeys are more complex. Human’s MN appeared to function in more parts of the brain. Different mirror actions take place in the premotor cortex, supplementary motor area, primary somatosensory cortex, and frontal and inferior parietal cortex (Molenberghs, Cunnington & Mattingley 2009). Nowadays, there are mostly two sides of the research, such as biological and others. Psychologists, philosophers, and evolutionists argued about it, too but compared to biological articles, there are not many works reflecting that point of view. The proposed origins of the MN usually correlate with genetics, evolutionary reproduction, simple associative learning or pre-adaptation from the side of evolution.
First experiments on macaques opened a variety of ways to examine MN. The most interesting part of the discovery was the answer of neurons to different stimulus. The scientist confirmed that MS took part in some monkey’s actions. Some experiments with food, sounds and different operations led to the theory that monkeys used MS to adapt to different situations. The reason why this theory appeared is that young monkeys could copy mimics and actions of humans (Ferrari et al. 2006). So this fact probably speaks for the associative learning origin of the MN. However, adult monkeys do not use MS for that purpose. Adult species learned everything they needed to survive and the only way they use MN is to watch other monkeys and understand why and for what purpose they act in particular ways. So the other reason for monkeys is to avoid and dangerous situation, to find possible ways to get food, etc. (Rizzolatti & Arbib 1998).
Humans’ MN is a more complicated topic. Firstly, functional magnetic resonance imaging (fMRI) has shown MN action inside inferior frontal cortex and superior parietal lobe when a person does something himself or sees someone doing the same thing (Iacoboni et al. 1999). That is why scientists thought that that part of the brain was the current MS in humans. But newer experiments measured the same activity on the other sides of the brain. The other thing was that MN cannot act as single neuron activists. That was the fact until 2010 when Mukamel et al. captured the single action of neurons (Keysers & Gazzola 2010). He studied brains of the patients with the epilepsy disorder. The research presented an interesting fact that some neurons activated only when someone was doing something or observing the act. The best part of this experiment was that some neurons acted completely different to the MN. These neurons had an opposite action when the patient was watching the action. The particular areas of interest were the motor and temporal cortex areas of the brain. However, these two brain’s regions are not the same as monkeys’. But it is not because monkeys do not have MN there, and not because humans do not have MN in other regions of the brain, but because the measures usually take place in those sides of the brain. The main point is that the mentioned parts of humans’ and monkeys’ brains can represent the most active type of the MN action (Gazzola & Keysers 2009). However, fMRI reports MN activity in the whole brain though it is impossible to say how this action correlates with MS. It is hard to state that the work of MN or just couple neurons fire with the help of neighbors. Some other studies reported that humans did not actually have more MN than monkeys but those were the approximate results. It is complicated to name any neuron as mirror because the actual MS can recruit other types of neurons to act in needed ways (Molenberghs, Cunnington & Mattingley 2012).
However, not every scientist takes the existence of the MN as a fact. Some of them think that MN does not exist in humans at all. It is understandable, because there are not particular evidences to show that the actual group of neurons acts as a mirror except Mukamel’s experiments with epileptic people. And even these experiments are not 100% proof. According to Pascolo, Hickok, etc. there are no clear statements and evidences that MN form the actual new class of neurons specializing on mirror actions (Pascolo, Ragogna & Rossi 2009). These scientists represent the idea of MN as the simple response of the motor system. Dinstein et al. (2008) focused on the problem of inconsistency of the motor system and MS. Other scientists also argued about the selective type of the experiments and about unconvincing results.
Lingnau, Gesierich & Caramazza (2009) conducted another interesting experiment. They came up with the idea to test a person while he is doing something and then observe it, and compare it with the result of the reverse test when the same person will first watch an action and after that actually do it himself. The measures reported the dissonance between the neuron actions during the two different experiments. The scientists concluded that this was a sign of a failure of the MN theory. It was based on the fact that thee was no adaptation in those people who, firstly, see the task and then complete it themselves. Kilner et al. (2009) disproved this evidences with another experiment that was almost the same as Lingnau’s but had the goal in the first place. MS explained the prediction of the goal-relative actions held by the Guinean people.
The other side of the problem was explained by Greg Hickok (2009); he challenged the theory of the MN existence as a well-known fact. He pointed to the mistake that people use MN to feel the other person, and monkey to understand another monkey. He built this strong statement on the ground of unconvincing test with monkeys and humans and highlighted the physiological and neuropsychological dissonance in this theory to refute it.
The other interesting statement appeared in Vladimir Kosonogov’s research (2012). He started to think about the problem from the point of goal-dependence. As Kilner et al. (2009) proved the relativity of the action and its goal for the MN to activate, Vladimir evaluated the possibilities that could exist on the neurological level. The dissociation was in the fact that MN activated only when they recognized the goal-directed action. The problem is how they understand that goal. The only explanation from his point of view was that understanding takes place in other brain parts.
However, not only scientists, but also philosophers argued about this problem. Patricia Churchland responded to this subject in her book Braintrust (2011). In chapter 6, she highlighted the dissonance in the issue that MN can take part in understanding people’s intentions, acts and feelings. She built the point that MN cannot understand such complex behavior by itself. It should be a harder way of the understanding achievement because neurons are not intelligent. Neurons are just cells, the part of the intellectual that might do it. And even though the person can theoretically understand the task, it does not mean that he or she will be able to accomplish this goal.
On the top of these problems there is one more that correlates with evolution. Cecilia Heyes (2009) declined the statement that MN is the basement of the evolution. Her thoughts are different. She thinks that MN is only the type of social adaptation but not the core of the associative learning that can influence the evolution. However, Ramachandran (2000) have exactly opposite feelings about this problem.
The development of the MS falls on the first 12 months of age (Terje, Gustaf & von Hofsten 2006). Scientists cleared the statement that the MS can be trained through the associative learning (Brass & Heyes 2005) and Hebbian theory (Keysers & Perrett 2004). However, it is still impossible to understand clearly how newborn humans can perform that type of learning.
The most interesting questions in the discussion about MN and MS correlate with the potential of this theory. One of the most common associations with the MN definition is that someone can understand another person’s intention with the help of the MS. To support this idea, the scientists recorded the action of the MN in macaques (Fogassi et al. 2005). The experiment included a monkey that watched a man grasp an apple and eat it or grasp it and put it away. 15 out of 19 neurons fired when the monkey saw the action that correlated with the eating activity and did not act when the scientist put the apple away. Other 4 MN represented the opposite measures, they activated only when the person put the food away. The interesting point was that the authors recorded the MN function before the act of eating or rejection of the food. So the actual act of grasping could work as a stimulus for the prediction of the final goal of the act (Fogassi et al. 2005).
Another way MN can influence our life can be the learning facilitation by memorizing the performances, goals and results. MN can help people to react or simulate different aspects faster with the clear program of the action. It correlates with associative learning and adaptation. The wider the variety of programs the person has, the faster and better he or she learns things or adapts to different situations (Kosonogov 2012).
Many scientists, especially Cristian Keysers (2011), independently started to research the relations between MS and empathy. They proved experimentally that MN can fire when people experience an emotion or watch someone experiencing it. Emotions can be different: disgust, pain, happiness, fear, etc. (Wicker et al. 2003). But the regions where the MN action takes place differ from the typical parts of the actions in the brain and the authors did not examine monkeys. An interesting fact is that people who describe themselves as empathic (passing a special test questions) have more active MN in their brain (Gazzola, Aziz-Zadeh & Keysers 2006). So the MS system can be described as a self-relative system.
Another philosophical and psychological point of view is that MN can help human with their self-awareness. Ramachandran (2009) wrote about the secondary self-representation. The person can look at herself or himself and try to predict the action based on the experience or try to understand the past performances. That can be used for deeper understanding of the personal character, improving self-understanding, and learning.
The MRI studies reported that the MN performed in the inferior frontal cortex. That is close to Broca’s area. One of the hypotheses is that this area is a language region. So the actual learning, imitation, understanding of the actions, etc. can take part in the development of the speech in newborn humans. The result of the experiments represented actions of the MN while two experimenters tried to explain words using mimics, hands, etc (Schippers et al. 2010). That can be the sign of the potential repetition of the language and speech of the newborn children. So the MS can explain how babies learn to talk.
Some researchers thhink that automatic imitation is mediated by the MS. It implies the actions and movements that can be performed unintentionally. It is almost similar to reflexes. Potentially a stare can be the sign of the mirror neurons. Another example is how people maintain posture. If it is the actual goal of the person, he or she tries to perform it better, but if the goal is, for example to go to the bathroom, they will not pay attention to this action. This phenomenon can be explained by the fact that people activate their MN when they think about someone maintaining posture, according to their experience and task, but if the task is different the association will be wrong, so they will not do it properly (Kosonogov 2011).
Automatic imitation can be the part of social behavior. But the motor mimicry can usually influence this behavior too. The research represents how it can help people to create affiliation and rapport (Lakin & Chartrand 2003). Mimics and gesticulations can theoretically fire the MS to create images that will help us to understand the opponent, believe him or to feel something. Some researches came up with the idea that the motor mimicry and automatic imitation are the same in terms of the mirror effect, which can be the tool to examine and study social attitudes and behaviors (Heyes 2011). The imitation studies suggest that MS is active during imitation but there are no published works that recorded the actual single MN action. However, it is a fact that the areas of MS take part in the imitation (Molenberghs, Cunnington & Mattingley 2009).
One of the most concerning topic that correlates with MN is autism. EEG and fMRI can record the brain response to different stimulus. Thus when someone sees another person moving, EEG and fMRI will detect the suppressed fire in the brain’s motor areas. It explains how people separate their own and someone’s actions when they are the same. Astonishing news was that autism led to the decrease of inhibition. Oberman, Ramachandran and Pineda (2008) published the research that represents interesting results. They supported the theory of interdependence of autism and MS and the new measures. Children with autism had functional, but less sensitive MS than normal children. Urgently after that Patricia Churchland (2011) responded that those measures could not represent the performance of MS. But at the end coroners reported differences between normal adults and adults with autism. The parts of the brain where scientists reported the MN action were smaller in the brains of adults with autism than in the normal brains. That led to the conclusion that MS disorders could influence social skills, imitation and other functions concerning MN (Hadjikhani et al. 2006). On the other hand, MN alone cannot fully explain the disorder. As explained, there were no results with actual recognition of the special neurons by themselves. Moreover, Dinstein and colleagues found normal MN activity in people with autism (Callaway 2010). The problem is not one sided and requires more research to support the topic.
The most modern theory that also mentions MN is called “theory of mind”. It is almost the philosophical problem. It represents our ability to predict someone’s behavior and goals from our experience. For example, if we see someone going to the restaurant we can expect that he wants to have a meal and we can predict that he knows that this place can serve the food he wanted. The interesting fact is that if you know something that the object does not know, it does not matter; your conclusion will be the same. The way how theory of mind depends on MN is through the simulation theory. These theories differ in the point, that all predictions we make are based on our suggestions of how another person will act in situation with well-known final. That is how people can talk about MN. MS can help with simulation, interpretation and understanding. But these two theories developed earlier without any help of the MS research (Keysers & Gazzola 2007).
The last branch of the research concerns gender differences in MS. The studies by Cheng et al. (2008) reported the different action of the motor resonance in males and females. Females had stronger resonance than males. Other studies showed the differences in empathy in males and females. Females represented better ability to understand other person’s emotions during face-to-face interaction. The explanation can hide in the fact that females are more emotional and expressional than males. But final results concluded that males and females evenly recognize emotions of other people so there was no difference between males and females and the abilities were approximately the same (Schulte-Ruether et al. 2008).
So the research paper is the presentation of summarized information about modern topic called mirror neurons. Firstly, we tried to define the topic using the history and origins of the actual problem. Secondly, we compared the possibilities, theories and data concerning monkeys and humans, highlighted some differences and patches. Thirdly, we found all the existing theories that tried to refute the possibility of the existence of the MN to counterweight the existing evidence. Fourthly, we found out that the development of MN started from the birth till 1 year old. Fifthly, we outlined the possible functions. Those are: understanding intentions (the experiment with the grasping of an apple to prove the possible existence of the MN and predictions of the final goal); learning facilitation (experience gaining, programming ourselves with the help of MS); empathy (feeling, experiencing personal or someone’s emotions); self-understanding (second-order representation, deeper understanding of the personality); language (theory about how babies can learn to speak and act in the society); automatic imitation (goal dependent actions); motor mimicry (social adaptation); correlation with autism (possible explanations of the disorder); theory of mind (personal assumption about someone else’s behavior, predictions); gender differences (how females’ MS is different from the males’ MS).