The functional role of the parieto -frontal mirror circuit: interpretations and misinterpretations

1. The functional role of theparieto-frontal mirror circuit:interpretations and misinterpretations GiacomoRizzolatti and CorradoSinigaglia

2. Basic knowledge • Mirror mechanism • Unifies perception and action • Its functional role depends on its anatomical location (different cortical areas, different species) • First discovered in ventral premotor F5 and particularly F5c sensory representations of the behavior of others motor representations of the same behavior in the observer’s brain

3. Basic knowledge • Motor act : A movement with a specific motor goal (such as reaching, grasping and manipulating) • Movement : A displacement of joints or body parts without a specific goal (generated spontaneously or produced artificially by electrical or magnetic stimulation of motor areas) • Motor action : Several motor acts organized in a chain, leading to the achievement of a specific motor intention (grasping a cup of coffee for drinking).

4. Aim • Focus on the parieto-frontal mirror circuit • Mirror based action understanding ?? The comprehension of an observed action based on the activation of a motor programmein the observer’s brain. The observed action is understood ‘from the inside’ as a motor possibility, rather than from the outside’ as a mere visual description. In macaque and human brain Anatomical organisation Functional role

5. The parieto-frontal mirror network in macaque • STS AIP and PFG(STShigh order visual information about biological motion, not motor properties , not mirror areas • IT AIP (object identity) • AIP,PFG  F5 • F5 connected with F6 (pre-SMA) and prefrontal cortex(area 46) Mirror neurons also in LIP and VIP !

6. The human parieto-frontal network the inferior section of the precentralgyrus, the posterior part of the inferior frontal gyrus • Brain imaging, TMS, EEG, MEG • two main regions the inferior parietal lobule, including the cortex located inside the intraparietalsulcus Single-subject fMRIanalyses evidence that other cortical areas (the primary and secondary somatosensory cortices and the middle temporal cortex) become active during action observation and action execution

7. What do parieto-frontal mirror neurons encode?

8. Evidence for goal coding in monkeys F5 motor neurons encode motor acts not movement Similar results for IPL • The mirror neurons in F5 and IPL do not differ in their motor properties from parieto-frontal motor neurons that do not have visual properties. When they fire in motor act observation, they send information about the goal of the observed motor acts • Different degrees of generality • strictly congruent (grasping with a particular grip) • broadly congruent (grasping achieved in different ways)

9. F5 mirror neurons- spatial relationships between the agent and the observer mirror neurons may encode the goal of the motor acts of another individual in an observer-centred spatial framework The observer can organize his own future behavior in cooperation or competition with the observed individuals.

10. Evidence for goal and single-movement coding in humans (1) fMRI studies • video clips with human or robot arms grasping an object or by using a tool • activation of parieto-frontal mirror neurons • tools a rostralsector of the left anterior supramarginalgyrus • aplasic individuals (without arms and hands) • parieto-frontal mirror circuit that was active during movements of the feet and mouth was also recruited by the observation of hand motor acts that they have never executed but the motor goals of which they could achieve using their feet or mouth! • TMS and fMRI studies, listening to action-related sounds

11. Evidence for goal and single-movement coding in humans (2) • the parieto-frontal mirror circuit of humans also becomes active during the observation of individual movements (not goal-related), TMS experiments observation of movements of others results in an activation of the muscles involved in the execution of those movements ???

12. Understanding the actions of others • Observing actions performed by another individual elicits a motor activation in the brain of the observer similar to that which occurs when the observer plans their own action • F5 mirror neurons in monkey fire in the absence of visual information describing the motor act of the experimenter.

13. Criticism (1) • Csibra : “if mirror activity represents a copy of the observed motor act, it is not sufficiently general to capture the goal of that motor act; conversely, if it is sufficiently general for goal understanding, it cannot be interpreted in terms of a direct matching mechanism between sensory and motor representations” two kinds of sensory–motor transformation movement mirroring, mapping the observed movements onto theobserver’s own motor representation of those movements goal mirroring, mapping the goal of the observed motor act onto the observer’s own motor representation of that motor act

14. Criticism (2) • goal understanding  STS (visual analysis of actions of others) • Only neurons that can encode the goal of the motor behaviour with the greatest degree of generality can be considered to be crucial for action understanding • STS  spatio-temporally adjacent visual representations of body part movements. not visual • representations of the same motor goal achieved by • different effectors • Parieto-frontal mirror neurons can be triggered by different visual stimuli (for example, hand and mouth actions) that have a common goal (for example, grasping)

15. Also…TMS adaptation paradigm • specific neural populations within the stimulated cortical region can be targeted. • One population is ‘adapted’ and will therefore be less active. • TMS targets less active neural populations  the adapted • population will be facilitated more strongly by TMS • Adaptation-inducing videos of a hand or foot acting on various objects and asked to respond as quickly as possible to a picture of a motor act similar to that of the movie • TMS over ventral premotor cortex, IPL and STS • TMS over both premotorand IPL  reaction times to ‘adapted’ motor acts regardless of the effector performing the observed motor act • TMS over STS  reaction times to ‘adapted’ motor acts only if the same effectorexecuted the act in the movie and in the test picture

16. Critisism (3) • There are several behaviouralinstances in which individuals understand the actions of others even if they are unable to perform them. Inferential reasoning : The capacity to attribute to an agent mental states that might account for the observed motor action in terms of the reasons (needs, desires and beliefs) underlying it. Broadly congruent mirror neurons

17. However…non mirror mechanism ? • What about the parieto-frontal mirror circuit when we observe actions that do not belong to human repertoire ?? • Dog biting vs. dog barking !!!! • STS active in all cases

18. Mirror-based action understanding ? True or false ? • STS recognition of the visual aspects of motor behavior • When the observed action impinges on the motor system through the mirror mechanism, that action is not only visually labeled but understood the observed action is understood from the inside as a motor possibility and not just from the outside as a mere visual experience

19. Understanding motor intentions of others - macaque • IPL, F5: action-constrained mirror neurons ‘Chains’ of neurons in which each neuron encodes a given motor act and is linked to others that are selective for another specific motor act. Together, they encode a specific motor action (for example, grasping for eating or grasping for placing ). The same neurons have mirror properties Why the individual is performing the action

20. Understanding motor intentions of others -human • fMRI right parieto-frontal mirror circuit during action understanding • Experiment of Cattaneo: grasping for eating and grasping for placing, EMG myolohyoid muscle both execution and observation of the eating action produced a marked increase of mylohyoid muscle activity as early as the ‘reaching’ phase, whereas no mylohyoid muscle activity was recorded during the execution and the observation of the placing action As soon as the action starts, the entire motor program for the action starts  intention, anticipatory representation of the motor behavior of another individual

21. Intention understanding is a multi-layer process involving different levels of action representation, from the motor intention that drives a given chain of motor acts to the propositional attitudes (beliefs, desires and so on) that — at least in humans — can be assumed to explain the observed behavior in terms of its plausible psychological reasons • Mentalizing network anterior sector of anterior cingulate cortex and other areas ? understanding the reasons behind an agent’s motor intention requires additional inferential processes

22. The mirror mechanism and autism

23. Conclusions • Mirror mechanism basic mechanism that unifies action execution and action observation, allowing the understanding of the actions of others from the inside (goals, intention, anticipation, prediction) • a primary way in which individuals relate to one another, as shown by its presence not only in humans and monkeys, but also in evolutionarily distant species ???

24. Thanks for your attention !!! Vasiliki ! Katerina!