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Mirror neurons: the basis of social learning and cognition

Final Activity Report Summary - MIRROR NEURONS (Mirror neurons: the basis of social learning and cognition)

One of the building blocks of social behaviour is the understanding of intentions, actions and emotions of others. Ground-breaking work of Rizzolatti and colleagues (Rizzolatti et al., 2001) designated the importance of the activation of so-called mirror neurons as a way to understand the intentions, actions and emotions of others. These neurons, located primarily in the ventral premotor area and inferior parietal lobule of the brain, are activated not only when performing an action oneself, but also while observing someone else perform that action. It is believed mirror neurons allow us to directly understand the actions of others by internally mimicking (simulating) these actions. There is no need for cognitive interpretation and/or reflection. Such simulation can be measure on both behavioural and neural levels. Observing another person performing a certain action facilitates execution of a similar action in the observer (motor priming). Observing another person's action also activates the mirror neuron system (MNS) in a somatotopic manner (i.e. observing a hand, activates hand brain area, while observing a foot activates the foot brain area).

The goal of the present line of research was to examine how the mirror neuron system is affected by understanding of the meaning of the observed action. If mirror neuron system is directly involved in action understanding than at some level of processing it should be able to dissociate between the same actions that have different meaning. We chose understanding of correctness of observed action in the context of an arbitrary task as a paradigm to study this issue. First, we examine whether observation of incorrect actions leads to motor priming and whether the degree of priming is modulated by action meaning. We used a task in which participants had to observe hand movements of another person and decide whether they were correct and incorrect. Specifically, the actor had to open his hand when a green circle appeared on the screen and to close his hand when a red circle appeared on the screen. The actor made erroneous movements on 25% of the trials.

During the action observation participants heard a tone and had to either open or close their own hand in response. Observer's own response was constant within a block of trials and therefore not related to the response performed by the actor. We found that although observing erroneous action slowed the observers down, they were always faster to respond when their response matched the actor's response. Importantly, the magnitude of this motor priming was not modulated by correctness of the observed action.

Secondly, we recoded ERPs in the similar paradigm and our preliminary results indicate that participants were covertly simulating an action before and after they saw the action. This was evident in a readiness potential (RP) lateralized to the centro-parietal areas in the left hemisphere (since a right hand was observed). Consistent with our behavioural experiment this simulation was not different between correct and incorrect actions. Together with the motor priming results this indicates that the process of mirroring the observed action using own motor system may serve as passive input needed for higher order process of action understanding.

We also found that when participants observe another person making a correct movement a negative potential, resembling error-related negativity (ERN) was present at the central electrodes. However, this potential was larger on correct trials, while the ERN is typically present on the erroneous actions for self-made errors.

Our results suggest that monitoring the task performed by another person is different from performing the task by yourself. Since participants were looking for errors it is likely that they were anticipating and simulating an erroneous response and observing a correct response was inconsistent with their expectations. Therefore, ERN-like activity during action observation could represent a deviation from expectation instead of experiencing other person's error as one's own. MNS probably provides the basis for action understanding but does not carry out understanding by itself.