Mirror neuron functioning: an explanation for gender differences in empathy?

2 Table of contents . 3 1. The mirror neuron system in humans . 4 1.1 Evidence for a mirror neuron system in the human brain . 4 1.2 Conclusiveness of the found evidence . 5 1.3 Measuring the level of mirror neuron activity . 5 2. The importance of mirror neurons in everyday functioning . 7 2.1 Mirror neurons and imitation . 7 2.2 Mirror neurons and empathy . 9 3. Mirror neurons and autism spectrum disorders . 10 4. Gender differences . 13 5. The autistic male brain . 16 Discussion . 19 Summary . 21 References . 22 Mirror neuron functioning: an explanation for gender differences in empathy? 4 The mirror neuron system in humans Evidence for a mirror neuron system in the human brain The first article on mirror neurons was published eighteen years ago; tungsten microelectrodes were used to record 184 single neurons from inferior area 6 (F5) of the macaque‟s brain, while acting and observing actions. The results showed that specific neurons in the monkeys‟ brain, that discharge during making certain goal directed movements, also discharge when observing another individual making these movements (Pellegriono, Fadiga, Fogassi, Gallese and Rizzolati, 1992). These neurons were called mirror neurons, and it was stated that they become activated during movement observation as well as during execution of that exact same movement. After this concept of mirror neurons was born, a lot of research followed, trying to prove the presence of these neurons in human beings. The first experiment on human mirror neurons contained a magnetic stimulation study (Fadiga, Fogassi, Pevesi and Rizzolati, 1995). While being stimulated on the left motor cortex, subjects observed another person making goal directed (the grasping of an object), and pointless (the tracing of geometrical figures in the air) movements. Stationary objects and light dimming were observed as a control condition. The motor evoked potentials of four different muscles (involved in the movements that the participants were observing) that were recorded during these tasks, showed a significantly increase in the first conditions in comparison to the control conditions. This outcome indicates that the activity of the motor system had increased during observing movements made by another person, and that therefore it could be possible for humans, to be in the possession of a system resembling to the one found in monkeys. This involvement of the motor system in movement observation was also demonstrated with the use of a quantified electro encephalography (qEEG). Cochin, Barthelemy, Lejeune, Roux and Martineau (1998) recorded qEEG signals from participants while watching an individual perform actions and while observing moving and stationary objects as control conditions. Neural activity in centro-parietal regions of the brain was found in the experimental condition, were this was not found in the control conditions, indicative of involvement of the sensimotor cortex in movement observation. Neuro-imaging studies also contributed to the increased probability of the existence of a Mirror neuron functioning: an explanation for gender differences in empathy? 5 MNS (mirror neuron system) in human beings, for example with the use of functional magnetic resonance imaging. Iacoboni and colleagues (1999) performed an fMRI on subjects while they were watching someone else move their fingers and while performing finger movements of their own. During this action and action-observation two areas were found in which overlap in activity was present; the inferior frontal cortex and rostal-most region of the right superior parietal lobe. This overlap in activity could indicate that neurons in those areas were firing in both conditions and that therefore mirror neurons are present in those specific regions of the human brain. Conclusiveness of the found evidence Research as described above does makes it likely to believe that humans are in the possession of a system resembling to the one found in monkeys. However, a recent article by Turella and colleagues (2007) argues that from the great range of research on the topic of mirror neurons in humans, due to inaccurate designs and methodological problems no study is sufficient enough to prove this existence of mirror neurons. Additionally, even though many different techniques were used in attempt to prove the presence of a MNS in human beings, al these methods (EEG‟s, MRI‟s, TMSand PET-studies) are only capable of providing indirect evidence for this concept, since they are unable to record single neurons. Therefore, the evidence of previously described research cannot be seen as conclusive, and it cannot be concluded that human beings are in the possession of a so called mirror neuron system. Unfortunately, single neuron recording, that was used to prove the mirror neuron existence in monkeys, is unethical in human beings, so the question remains if there ever will be conclusive evidence for the existence of human MNS. Currently the mirror neuron debate is still going on; a consensus has not been reached. However, the many research concerning this issue does make a reasonable case for its existence in human beings. And even though the presence of mirror neurons in humans cannot be directly proved, this study starts from the idea that our brain is in the possession of them. Measuring the level of mirror neuron activity The research discussed above, is indirect prove of a MNS in human beings. It is expected that the amount of mirror neuron activity is different for different people, brain areas and situations. However, to measure the level of mirror neuron functioning, the methods used above are not sufficient enough. For measuring the functioning of the MNS, the electroencephalographic μrhythm has been proposed. The μ-rhythm is a specific α-rhythm that can be measured with the Mirror neuron functioning: an explanation for gender differences in empathy? 6 use of an EEG-scan. This EEG μ-rhythm is produced in the sensorimotor cortex and ranges between 8 and 13 Hz. During rest, this rhythm is most prominent, when moving or observing biological movements it is attenuated (Muthukumaraswamy, Johnson and McNair, 2004). It is proposed that attenuation of the EEG μ-rhythm reflects desynchronization of the cell assemblies lying underneath. This desynchronization therefore suggests that the load on these cells has increased (Pfurtscheller, Neuper, Andrew & Edlinger, 1997). The exact relationship between the μ-rhythm and mirror neurons is not clear. However, it has been proposed that the μ-rhythm might reflect ‘downstream modulation of motor neurons by cells in the premotor cortex, some of which are mirror neurons’ (Muthukumaraswamy, Johnson and McNair, 2004). Even though the relationship between the MNS and the μ-rhythm is unclear, for this study, μ-rhythm is considered to be a good method for indicating the level in which mirror neuron activity is present. Mirror neuron functioning: an explanation for gender differences in empathy? 7 The importance of mirror neurons in everyday functioning Mirror neurons and imitation Going from the concept that mirror neurons become activated during observing as well as during execution of an action, a hypothesis followed arguing that these neurons are at the base of an observation-execution matching mechanism. The idea of this mechanism is that during action observation the motor circuit produces an “activation pattern” that is also produced when the observer executes this particular action (Gallese, 2001). In other words; our motor system becomes activated as if we are performing an action, when in fact we are only observing one. This observation-executing matching system is thought to be important when it comes to actionunderstanding and -recognition (Muthukumaraswamy, Johnson & McNair, 2004). A similar idea was also proposed when trying to explain the process of imitation. During our daily activities imitation is an important quality to have at ones disposal. The process of imitation contains observation of a specific action, processing and executing. It is a process in which the brain can „plan‟ a movement after only observing one. The „direct matching hypothesis‟ was proposed; a hypothesis similar to the one described above. It also states that in the human brain, due to mirror neuron activity, observed actions are directly matched with a neural representation of that action. It is believed that this lies at the base of the ability to imitate observed behavior, and that