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We will now focus on the first system, which involves learning based on observation and imitation. The anatomical organization of the first system responds to a somatopic hierarchy of the ventral premotor cortex, being the motor acts of the legs located in the dorsal zone; the facial behaviors located ventrally, and the manual ones with an intermediate distribution. The location of proximal motor acts moving the hand towards a point are represented dorsally, while the simple act of grasping produces a ventral activity in the premotor cortex.

On the other hand, the observation of motor acts produces a differential activation in the parietal cortex, as well. The observation of transitive acts produces an activation of the intraparietal sulcus, as well as an activation of the parietal convexity adjacent to that area.

The observation of intransitive acts -regardless of whether they are symbolic acts or mimic repetition- find a specific activity in the posterior part of the supramarginal gyre, which extends to the angular gyre. Finally, the observation of acts performed with tools specifically activates the most rostral part of the supramarginal turn. The mirror neuron system produces an evocation of the observed motor actor within the premotor cortex itself. This activity is coordinated at the same time in the parietal lobe.

It is necessary to differentiate the sequence of observation processes in order to correctly delimit the neuronanatomy of the first exposed system frontoparietal. In this system, we will talk about observed behaviors that suppose a visuomotor priming for the execution -or not- of an action. Therefore, we will exclude the conception of motorvisual priming, which implies predictions of consequences during the planning of actions. In other words, a human observing a bark does not activate the premotor and parietal areas, since it does not possess that behavioral repertoire in the cortex.

On the other hand, the activity of the system is proportional to the experience of the observer in the behavior he is observing. The functional connectivity of the frontoparietal system of mirror neurons presents a sequence during observation.

Originally this sequence originates in the occipital lobe, where the main characteristics of the observed stimuli are recorded. All the information is sent to the integration areas in a series of steps that vary from 20 msec. Iacoboni et al. For them, the dorsal zone of the pars is activated when the act is observed and when it is imitated; but a ventral activity only occurs when it is imitated. In fact, Iacoboni et al. For them, the mirror neuron system is fundamental for learning through imitation.

And the activation sequence would be completed as follows: i first there is an activation of the upper temporal furrow, where the ventral representations of the observed movements are found. From there ii is passed to a codification of action goals, through the frontoparietal system, in which the dorsal prefrontal cortex would be in charge of computing the different aspects of the action, such as the goal itself or the meaning, archiving this information, sending information to the parietal lobe and correcting computations over space.

This efferent information would be sent from the frontoparietal mirror neuron system, through the opercularis pars, to the upper temporal furrow again.

At this point, there would be a computation of the fit that exists between the predicted consequences in the planned imitative action, and the visual description of the observed action. In short, the frontoparietal mirror neuron system constitutes a learning system based on feedback. In fact, what is transferred from the visual areas to the motor areas is not a detailed motor program, but a prototype of the action, an action with meaning that is processed in the opercularis pars of the lower frontal rotation; and that then guides the motor planning according to a precise detailed representation of the observed action, represented in the upper temporal furrow and in the lower parietal lobe.

When the observed action is novel, before the execution period, there is an activation of the frontoparietal mirror neuron system, as well as an activation of the AB 46 area and the anterior medial cortex. This activation translates into an executive control mechanism, probably as part of the Shallice supervisory mechanism on which Baddeley relies to formulate the working memory mechanism.

In our case, such a system could involve a top-down motion planning computation, in which the working memory manages the observed contents and plans the motion based on them, producing a frontoparietal activity that corresponds to the mirror neuron mechanism. The mirror neuron system should not be conceived as a separate neuronal module, but as an intrinsic mechanism underlying most areas related to motor movements. In fact, and as we will see later, the disruption of this system does not cause a selective deficit in focal lesions.

Rather, the implication of this system is proven in disorders of the development of the nervous system, and in lesions of the frontal lobe. As mentioned above, the mirror neuron system overlaps with other systems, and the control system is no exception, as it suppresses spontaneous imitation behaviors. Frontal injuries cause a series of deficits characterized by the appearance of impulsive behaviors generated by external stimuli.

Normally, the condition arises from a bilateral lesion, although it may also be due to a less frequent unilateral lesion. The observation of the behaviour of others can elicit an activation of the premotor and parietal zones, dependent on the mirror neuron system. In healthy subjects, this activation does not occur because there is suppression by the frontal lobe. Its deterioration implies a destruction of these mechanisms, transforming potential acts into acts of fact.

The ecopraxia constitutes the forced and critical imitation of observed behaviors, normally with the presence of perseverations. Although it usually occurs as a disorder associated with damage to the basal ganglia, it is also produced by a frontal deterioration, which produces a disinhibition of the mirror neuron system.

A fundamental task of learning is imitation, which produces the development of some basic skills of social development, especially in the acquisition of gestural identification, postural, and allows the development of understanding of the intentionality of the other. These neurons are triggered when the subject performs behaviours related to a goal, but especially when he observes these behaviours in others, discriminating between the different components of the action according to whether they are more or less relevant from the intentional point of view; even before objects that are not present.

From the foregoing it can be deduced that mirror neurons not only handle contents related to motor or visual patterns, but also abstract, both in terms of the sensory modality of the contingency a sound with meaning and in terms of elements of a non-present or abstract nature, which present a relationship, in terms of learning, with intentionality, a reality in which the understanding of the motives of others plays an important role.

The integrated motor information presents significant procedural characteristics: processing of movement, of parts of the body, follow-up of the action aimed at a goal of an external subject, etc.

The proximity to frontoparietal systems that support various types of sensorimotor integration suggests that the coding of the action implemented in the mirror neuron system is linked to some form of sensory integration.

Imitation is one of the many forms of this type of integration. In such integration, the observing subject makes comparisons between the existing information in the primary areas visual inputs and the observed behavior, as explained above. This differentiation is observed at the neuronal level, distinguishing the interactions between the system of mirror neurons and preparation structures for prefrontal and parietal execution during learning by imitation, and the interaction between the system of mirror neurons and the limbic system during emotional contagion.

Probably, as we will discuss later, the mirror neuron system in autism also allows this distinction to be made, with one of the interaction systems being more damaged than the other. They are activated in the imitated action, but also in the action that is being observed even without imitating it.

They have two levels of congruence: strict, in which neurons are activated exclusively in substantially identical actions and observations; and approximate congruence, in which they are activated in response to the observation of an action that is not necessarily identical to the action performed, but achieves the same goal.

Activation thresholds are defined by the logic of the action, not by the object or the distance of the action.

From these properties it can be inferred that they handle abstract contents of the observed actions. But what is the degree of abstraction of this codification?

There is a sensory recognition of sonorous actions sonorous inputs in the mirror neuron system. This provides a basis for understanding speech and language as a code that is learned — at least in initial phases — through physical and gestural imitation.

As mentioned above, there is a functional hierarchy in the mirror neuron system when the subject observes a motor action in order to learn it. The basic levels of motor processing have been extensively studied. However, the mirror neuron system responds to a hierarchy in which the processing of movements is of high rank, producing computations between the consequences of the action and the goals.

In order to compute such knowledge, the components that present the context of the action must be dissociated: first, the object itself, which is the goal. Existing studies have not been conclusive until relatively recently. However, by means of neuronal suppression techniques such as Magnetic Stimulation, high-end processing has been dissociated from merely kinematic processing.

Therefore, there is differential processing of objects, even if the action is the same e. On the other hand, this dissociation also implies the analysis of the expected consequences of the action, which presents a higher hierarchy level than the previous one. It is very important to bear in mind that goal processing implies the processing of the movements necessary to achieve that goal, but they are aspects with a different level of processing, being the processing of the motor program not its planning a lower processing range.

They found that the consequences of an observed action are processed in the lower frontal rotation and lower right parietal lobe, as well as in the left postcentral groove and in the left intraparietal anterior groove. Together they have proposed a hierarchical model that is composed as follows: On the one hand, there is a low-level -cognitive- processing that involves the processing of the motor pattern. The processing of the motor pattern takes place in a system that involves both visual and motor analysis of the action.

Visual processing would be performed in lateral occipital areas, while kinematic pattern processing is performed in the lower frontal regions. High-level processing, defined by an analysis of goals, is performed in a system involving two areas of the right hemisphere: the intraparietal lobe and the lower frontal rotation — to a lesser degree.

In this goal processing, goal-objects are also processed laterally in the left lower parietal cortex. Is there a neuronal hierarchy when the observed actions are executed? Yes, and the hierarchical range differentiates the complexity of the actions, that is, when the actions are simple, when they are complex -composed by different steps-, as well as when they respond to an intentionality. In this case, the lateralization of neuronal activity does not seem so evident.

There is evidence that the planning of simple acts occurs in the motor and premotor cortex, as well as in the left lower parietal cortex. However, it appears that the lower right parietal lobe is involved in complex behaviors that require several steps, such as the London Towers task Newman et al. This area seems important for sending feedback on the consequences of the motor act, and next to the cerebellum it can compute corrections of movement in space or in planning.

This theory has been supported by several clues. Firstly, a left lateralization of the mirror neuron system has been demonstrated.

On the other hand, the activation of the mirror neuron system in the brain of the macaque allows to extrapolate its zones to ours: the areas in the macaque would coincide with the AB 44 of the human, adjacent to the Broca area.

From the theory of semantic expression, which proposes that language is learned in a bottom-up process, and from the motor theory of discourse perception, which proposes that the objective of discourse analysis is facial expressions associated with sounds, rather than sounds, it has been discovered that during discourse perception the motor areas of discourse are activated, which coincide with the mirror neuron system.

In addition, it has been discovered that the processing of linguistic material produces motor activation, and that the neuronal activity produced by the processing of linguistic material related to parts of the body and actions, activates the somatotopic zones of the brain related to reading.

The second mirror system is the emotional one. As we have said before, this system is involved in the adoption of empathic behaviors, but it does not necessarily work separately from the first system, although this point will be addressed later. The mirror neuron system is also located in cortical areas that mediate emotional behavior. Observing the pain of others produces an activation of the cingulate cortex, the amygdala, and the insula.

The insula is especially important in the integration of sensory representations, both internal and external. It has an agranular structure and is cytoarchitecturally similar to motor areas. Therefore, the insula functions as a communication node between the limbic system and the somatopic cortical activation associated with pain, both internal and external, which constitutes the evolutionary basis of empathy.

However, this base is not unique. The system of empathy would be framed in such a way: In the first place there must exist a node in this system, which is the amygdala, which is necessary for the emotional activation of the subjects. Secondly, the zones of expression and emotional regulation. Thirdly, the high-level processing node composed of the mirror neuron system. This system consists of the insula and the middle anterior frontal cortex.

The interaction of this system with emotion varies depending on the complexity of the emotional act. The mirror neuron system works in two ways when it comes to social cognition. First, it is necessary for prediction and attribution of thought theory of mind.

Secondly, it sets in motion mechanisms of affective recognition and expressiveness.


Books by Marco Iacoboni

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Marco Iacoboni

Marco Iacoboni, a neuroscientist at the University of California at Los Angeles, is best known for his work on mirror neurons, a small circuit of cells in the premotor cortex and inferior parietal cortex. What makes these cells so interesting is that they are activated both when we perform a certain action—such as smiling or reaching for a cup—and when we observe someone else performing that same action. In other words, they collapse the distinction between seeing and doing. In recent years, Iacoboni has shown that mirror neurons may be an important element of social cognition and that defects in the mirror neuron system may underlie a variety of mental disorders, such as autism. Mind Matters editor Jonah Lehrer chats with Iacoboni about his research. Did you immediately grasp their explanatory potential? I thought that mirror neurons were interesting, but I have to confess I was also a bit incredulous.


The Mirror Neuron Revolution: Explaining What Makes Humans Social


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