2009 Conference on Neuroesthetics
"Monkey Inferior Parietal Mirror Neurons Coding Action Semantic Equivalences"
The anterior portion of the inferior parietal area possesses comprehensive representations of actions embedded in behavioral contexts. Mirror neurons, which respond both to self-executed and observed actions, exist in this brain area in addition to those originally found in the pre-motor cortex. We found that parietal mirror neurons responded differentially to identical actions embedded in different contexts. Another type of parietal mirror neuron represents inverse and complementary property of responding equally to different, dissimilar actions made by self and others for an identical purpose. Here, we propose a hypothesis that these sets of inferior parietal neurons constitute neural bases to encode the semantic equivalence of various actions across different agents and contexts.
Pier Francesco Ferrari
"From Monkey Mirror Neurons to Behavior"
Mirror neurons belong to a class of neurons found in the premotor and parietal cortices of macaques which activated by both execution and observation of goal-related actions. These neurons would serve the recognition of others’ actions by matching the visual description of an action onto the monkey’s cortical motor representation of that action. The capacity to match the own behavior with that of others has been documented in macaques and other monkeys species by using a paradigm in which the monkey has to recognize when being imitated by a human experimenter.
More recent findings show that some mirror neurons could also enable the monkey to detect the motor intention of an individual. They discharged differently during the observation of a grasping act of the experimenter depending on the final goal of the action. A model based on action chains has been hypothesized to explain the behavior of these mirror neurons in the course of their visual discharge. During the observation of a grasping motor act that leads to a specific goal (for example eating) a specific neuronal chain is activated. In the observer, as well as during the motor performance, all the elements of that chains will be activated (for example reaching, grasping, bringing to the mouth, biting). This will therefore allows the observer to activate an internal representation of what, most likely, the acting agent is going to do, also by observing the first elements of the action. The temporary inactivation of this circuit produces impairments in the monkey performance that reflects the incapacity to recruit the proper motor chains for the achievement of a specific motor goal.
It has also been proposed that mirror neurons could be partly responsible of the primate capacity to repeat observed actions (i.e response facilitation and imitation). Several lines of research show that macaque and other monkey species are able to repeat observed familiar actions and basic imitative processes that do not require the acquisition of a new behavior. However, their possible direct role in mimicry has not yet been empirically demonstrated in the monkey.
Recently, electroencephalography in newborn macaques has shown that motor areas become active both during the observation and imitation of communicative gestures. Thus, infant macaques are provided at birth with a neuro-physiological mechanism, probably underpinned by mirror neurons, that allow them to understand others’ behaviors and intentions and to tune the own behavior with others in an interactive exchange.
"Mirroring People: Neural Mechanisms of Mirroring in Humans"
My talk will be divided in two parts. In the first one I will review brain imaging findings suggesting that human brain areas that presumably contain mirror neurons are important for imitation and empathy. In the second one, I will discuss recent data obtained using a rare clinical opportunity, that is, electrodes implanted in the depth of the brain of neurological patients. While the electrodes were implanted exclusively for medical reasons, we had the opportunity to measure responses from individual neurons of the human brain. We found mirror neurons in many human brain areas. We also found a new class of mirror neurons that may be important to control unwanted imitation and to differentiate self from other. The depth electrodes data in the human brain suggest that mirror neurons are pervasively represented in the brain and may provide an important cellular mechanism for understanding other minds.
"The properties of mirror neurons in the light of the organization of the motor system"
The neurophysiological studies of the last two decades have provided evidence that the motor cortex is not simply involved in movement programming and execution, but plays a main role in coding the goal of motor acts. This endows the motor cortex with a storage of motor representations (motor knowledge) that can be addressed by different types of sensory inputs through dedicated parieto-premotor circuits. The matching between sensory input and motor representation allows the emergence of different types of cognitive abilities. An example of the outcome of these matching mechanisms is represented by mirror neurons, found in both ventral premotor and inferior parietal cortex of the monkey. These neurons activate both when the monkey executes a hand or mouth motor act and when it observes a similar motor act performed by another individual. Some of them are activated also by the sound of the motor act (audiovisual mirror neurons). It has been proposed that the mirror neuron system underpins action understanding. More recent studies have demonstrated further properties of mirror neurons. First, they appear to play a very important role in understanding action intention. Second, a percentage of them appear to code also the sector of space in which the observed action is performed, suggesting a possible role decoding social information in order to interact with other individuals.
The mirror system does exist also in humans. The frontal and parietal areas activated during action observation are very similar to those containing mirror neurons in monkeys. Several studies demonstrated that in humans the mirror neuron circuit is involved not only in action understanding, but also in other important functions such as imitation, language, and emotion understanding. In addition, it is becoming plausible that this system can be an important tool in rehabilitation of patients with motor impairments.
"Human premotor cortex codes observed goal-related actions irrespective of the physical appearance of the agent"
Although a substantial body of evidence indicates that the “mirror” system chiefly represents the goal of the observed action, findings from a recent neuroimaging study in macaque seem to challenge this view. In particular, it was found that activity within a key “mirror” territory (premotor area F5c) during the observation of hand actions was modulated by the type of agent performing the observed action, i.e., a person in full view or an isolated hand. Area F5c responded for a model acting, but not for a hand-alone acting. This was taken as the demonstration that mirror area F5c was modulated by the physical appearance of the acting agent, even when the goal of the observed action remained the same. Naturally this contrasts with the idea that “mirror” representations are mainly related to the goal of the observed action.
Whereas a variety of neuroimaging studies have brought to the conclusion that a “mirror” system might exist in humans, no studies have investigated whether such system in its entirety or in a specific sector of it (e.g., the possible homologue of monkey area F5c) is differently alerted by the observation of different agents acting. Here I shall report on a study specifically designed to address this question. The results indicate that the ventral premotor cortex is similarly activated by both a model and a hand-alone acting. I shall contend that what is represented within the preemotor cortex is not bounded to the physical appearance of the acting agent, but it is a rather abstract representation centered on the goal of the action.
"Enactive Understanding and Motor Intentionality"
Most of our social interactions rest upon our ability to understand the behavior of others. But what is really at the basis of this ability? The standard view is that we understand the behavior of others because we are able to read their mind, to represent them as individuals endowed with mental states such as beliefs, desires and intentions. Without this mindreading ability the behavior of others would be meaningless for us. Over the last few years, however, this view has been undermined by several neurophysiological findings and in particular by the discovery of mirror neurons. The functional properties of these neurons indicate that motor and intentional components of action are tightly intertwined, suggesting that the basic aspects of intentional understanding can be fully appreciated only on the basis of a motor approach to intentionality. The aim of this paper is twofold: to develop this approach in order to account for the crucial role of motor intentionality in action and intention understanding below and before any meta-representational ability, and to shed new light on the ontogeny of mindreading, by explaining how the first forms of understanding in infants may be intentional in nature, even without presupposing any explicit and deliberate mentalizing.
Ilan M Dinstein
"The human mirror neuron challenge"
Since the discovery of mirror neurons in the macaque monkey over a decade ago, numerous studies have searched for their human equivalents. This endeavor has proven extremely challenging. The defining characteristic of monkey mirror neurons is that they are selective for particular movements whether observed or executed. We and others have recently used fMRI adaptation and classification techniques in attempts to isolate movement-selective cortical responses in humans. To estimate responses to particular movements we recorded fMRI responses as subjects repeatedly executed or observed a small number of hand movements. In the adaptation study we found that commonly described candidate “mirror system” areas exhibited adaptation (repetition suppression) when the same movement was executed repeatedly or observed repeatedly, a signature of movement selectivity. But there was no evidence for cross-modal selectivity (i.e., adaptation from executed to observed movements or vice versa), as would have been expected of mirror neurons. In the classification study we compared the responses across observation and execution of movement using multivariate pattern classification techniques. Our results showed that candidate human “mirror system” areas responded with distinctly different spatial patterns during the observation and execution of the same hand movement. Both of our studies suggest that fMRI responses in candidate human “mirror system” areas are mostly generated by distinct visual and motor neural populations rather than a single population of mirror neurons. While mirror neurons are likely to exist in humans, they seem to comprise only a minority of the neurons in “mirror system” areas. Our studies emphasize the difficultly in studying human mirror neurons and question the conclusions of previous fMRI studies on the matter. We suggest that finding a reliable methodology for isolating their responses in humans is essential to substantiate hypotheses regarding their role in understanding the actions/intentions of others, feeling empathy, learning by imitation, and understanding language.