Beyond unpleasantness: the interplay between social cognition and the somatic-affective states of pain and disgust

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Thesis

Reference

Beyond unpleasantness: the interplay between social cognition and the somatic-affective states of pain and disgust

ANTICO, Lia

Abstract

Embodied models argue that social cognition (e.g., understanding others' affective states, reacting to a mistreatment) is grounded in representations of basal sensory-affective experiences, such as pain and disgust. However, it is unclear whether the information accessed relates to sensory-specific representations of the first-hand state or instead to broader (supra-ordinal) dimensions that act orthogonally between different states, such as unpleasantness, arousal, or salience. In this thesis, I examined the role played by two qualitatively different (but comparably unpleasant) first-hand experiences of pain and disgust on emotional facial processing (Study 1), social exclusion (Studies 2 & 3), and the combination of the two (Study 4). I analyzed behavioural, physiological and neural responses (using fMRI) from healthy participants, which were engaged in a new experimental set-up developed for assessing whether pain and disgust influenced (or were influenced by) social behaviour in dissociated or comparable fashion at sensory-specific or supra-ordinal (unpleasantness) level.

ANTICO, Lia. Beyond unpleasantness: the interplay between social cognition and the somatic-affective states of pain and disgust. Thèse de doctorat : Univ. Genève et

Lausanne, 2020, no. Neur. 277

URN : urn:nbn:ch:unige-1405170

DOI : 10.13097/archive-ouverte/unige:140517

Available at:

http://archive-ouverte.unige.ch/unige:140517

Disclaimer: layout of this document may differ from the published version.

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DOCTORAT EN NEUROSCIENCES des Universités de Genève

et de Lausanne

UNIVERSITÉ DE GENÈVE FACULTÉ DE PSYCHOLOGIE ET SCIENCES DE L’EDUCATION Professeur Corrado Corradi-Dell’Acqua, directeur de thèse

BEYOND UNPLEASANTNESS. THE INTERPLAY BETWEEN SOCIAL COGNITION AND THE SOMATIC-AFFECTIVE STATES

OF PAIN AND DISGUST

THESE

Présentée à la Faculté de Psychologie et

des Sciences de l’Education de l’Université de Genève

pour obtenir le grade de Docteure en Neurosciences

par

Lia ANTICO

de Loreto Aprutino (Italie)

Thèse N° 277 Genève Université de Genève

2019-2020

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To the women of my life,

mum Mafalda and grandma Iolanda

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Placer le rêve et l’émotion au cœur de l’aventure scientifique

Bertrand Piccard

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Abstract

The inspiration for this dissertation comes from the desire to study social interactions, and how we understand other people’s affective states. In those situations, we wanted to know what type of information is taken into account while we recognize others’ emotions or we experience social misconduct, and how this information shapes our somatic and affective experience.

Extended research in psychology and neuroscience supported embodied models of social cognition, arguing that several key elements of our inter-personal relationships (e.g., understanding others' affective states, reacting to a mistreatment) are grounded in representations of basal sensory-affective experiences, such as pain and disgust. However, it is still unclear whether the information accessed relates to sensory-specific representations of the first-hand state or instead to broader (supra-ordinal) dimensions that act orthogonally between different states, such as unpleasantness, arousal, or salience. For instance, it might be that when people observe pain in others, they simulate on their own body either the same detailed aching experience (sensory-specific representation), or a more general discomfort common also to disgust (supra-ordinal representation).

To address this question, we tested the role played by two qualitatively different (but comparably unpleasant) first-hand experiences of pain and disgust on: emotional facial processing (Chapter 2), social exclusion (Chapters 3 & 4), and the combination of the two (Chapter 5). Across four studies, we measured behavioural, physiological, and neural activity in approximately ~ 230 neurotypical individuals, with the aim of assessing whether pain and disgust influenced (or were influenced by) social behaviour in dissociated or comparable

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fashion, and therefore to isolate influences occurring at sensory-specific or supra-ordinal (unpleasantness) level.

Chapter 2 describes a study testing whether the representations of first-hand pain and disgust affected the subsequent classification of facial expressions of pain, disgust, surprise (arousing neutral control), and hybrid combinations thereof. We found that the evaluation of others’ facial expression was influenced by the prior experience, with more frequent pain classifications following thermal stimuli, and more frequent disgust classifications following olfactory stimuli. Critically, this modulation was cross-modal in nature, as facial traits of diagnostic of both pain and disgust (but not those of surprise) were biased in comparable manner by each first-hand stimulation. This suggests that one’s aversive experiences and the appraisal of others’ facial responses share a coding information that is best described in terms of supra-ordinal representation of the unpleasantness (but not arousal) of the experience.

In the studies described in Chapters 3 and 4, participants were engaged in a virtual- tossing ball game (Cyberball), in which they were included and excluded by confederates.

Subsequently, they were asked to rate the unpleasantness of thermal painful and olfactory/gustatory disgusting stimulations. The behavioural and physiological results (Chapters 3-4) revealed that social exclusion led to reduced sensitivity to pain, with lower subjective unpleasantness ratings and decreased cardiac responses. Furthermore, the analysis of brain activity (Chapter 4) revealed that social exclusion, as opposed to inclusion, showed higher response of posterior insular and opercular regions, structures often involved in sensory-discriminative components of the pain experience. Furthermore, pain-related neural response in the posterior insula decreased following social exclusion, whereas increased signal was observed at the level of the dorsal and ventral medial prefrontal cortex, regions often

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implicated in cognitive control and affect regulation. Finally, the implementation of a priori neurological multivariate models for pain and cognitive control revealed a decrease of brain signal informative about physical pain during exclusion, but also an increase of brain signal informative about cognitive control. None of the modulations observed for painful behavioural, physiological, and neural responses generalized to the case of disgust. Overall, these results show that social exclusion influences preferentially the sensitivity to pain, thus suggesting that the interplay between sufferance of physical and social nature is best interpretable in terms of a pain-specific coding.

Finally, Chapter 5 describes an experiment in which we combined the two paradigms from the previous studies, by replacing the thermal and olfactory stimulations used in Chapter 2 with Cyberball gaming sessions. This was aimed at testing whether social exclusion is sufficiently similar to thermal pain to lead to the same influence in the appraisal of facial expressions. Unfortunately, we found no evidence in favour of this hypothesis. Instead, social exclusion seemed to facilitate specifically the recognition of disgust, an effect interesting in its own right, but unrelated with the main experimental question of the present dissertation.

Overall, our results confirm seminal accounts that social behaviour shares some representational levels with first-hand pain and disgust. However, it seems that different social processes underlie different components underlying these somato-affective experiences: the evaluation of others’ states shares a supra-ordinal code of unpleasantness, whereas social exclusion appears to tap a pain-specific representation, possibly encoding information about sensory properties of the aching experience, or/and mechanisms for its regulation. Indeed, the two pain-specific and supra-ordinal components seem distinct from

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one another, as social exclusion does not influence the evaluation of facial expression in the same way as thermal pain.

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Résumé

L’inspiration de cette thèse vient du désir d’étudier les interactions sociales et la façon dont nous comprenons les états affectifs des autres. Dans ces situations, nous voulions savoir quel type d’information est pris en compte lorsque l’on reconnaît les émotions des autres ou que l’on subit des inconduites sociales, et comment ces informations façonnent notre expérience somatique et affective.

Des recherches approfondies en psychologie et en neurosciences ont soutenu des modèles incarnés de la cognition sociale, faisant valoir que plusieurs éléments clés de notre relation interpersonnelle (par exemple, comprendre les états affectifs des autres, réagir à un mauvais traitement) sont fondés sur des représentations d'expériences sensori-affectives basales, telles que la douleur et le dégoût. Cependant, on ne sait toujours pas si les informations récoltées concernent des représentations sensorielles spécifiques à l'expérience propre, ou plutôt des dimensions plus larges (supra-ordinales) qui agissent orthogonalement entre différents états, telles que le désagrément, l'arousal ou la saillance. Par exemple, il se peut que lorsque les gens observent la douleur chez les autres, ils simulent sur leur propre corps, soit la même expérience douloureuse détaillée (représentation sensorielle spécifique), soit un inconfort plus général commun également au dégoût (représentation supra-ordinale).

Pour répondre à cette question, nous avons testé le rôle joué par deux expériences qualitativement différentes (mais comparativement désagréables) de douleur et de dégoût sur: le traitement émotionnel du visage (chapitre 2), l'exclusion sociale (chapitres 3 et 4) et la combinaison des deux (chapitre 5). À travers quatre études, nous avons mesuré l'activité comportementale, physiologique et neurale chez environ 230 individus neurotypiques, dans le but d'évaluer si la douleur et le dégoût ont influencé (ou ont été influencés par) le comportement social de manière dissociée ou comparable, et donc isoler les influences

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survenant en manière spécifique au niveau sensoriel ou supra-ordinal (liée, par exemple, au désagrément).

Le chapitre 2 décrit une étude testant si les représentations de première main de la douleur et du dégoût ont affecté la classification ultérieure des expressions faciales de la douleur, du dégoût, de la surprise (un contrôle arousing neutre) et des combinaisons hybrides de celles- ci. Nous avons constaté que l'évaluation de l'expression faciale des autres était influencée par l'expérience antérieure, avec des classifications de douleur plus fréquentes suite à des stimuli thermiques et des classifications de dégoût plus fréquentes après des stimuli olfactifs. De manière critique, cette modulation était de nature intermodale, car les traits du visage de diagnostic de la douleur et du dégoût (mais pas ceux de la surprise) étaient biaisés de manière comparable par chaque stimulation de première main. Cela suggère que les expériences d’aversion et l’évaluation des réponses faciales des autres partagent une information de codage qui peut être mieux décrite en termes de représentation supra-ordinale du désagrément (mais pas de l’excitation) de l’expérience.

Dans les études décrites dans les chapitres 3 et 4, les participants étaient impliqués dans un jeu de ballon virtuel (Cyberball), dans lequel ils étaient inclus et exclus par les autres joueurs.

Ensuite, on leur a demandé d'évaluer le caractère désagréable des stimulations thermiques douloureuses et des stimulations olfactives / gustatives dégoûtantes. Les résultats comportementaux et physiologiques (chapitres 3-4) ont révélé que l'exclusion sociale conduisait à une réduction de la sensibilité à la douleur, avec des évaluations de désagrément subjectif plus faibles et une diminution des réponses cardiaques. En outre, l'analyse de l'activité cérébrale (chapitre 4) a révélé que l'exclusion sociale, par opposition à l'inclusion, conduit à une réponse plus élevée des régions insulaires et operculaires postérieures, des

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structures souvent impliquées dans les composantes sensori-discriminantes de l'expérience de la douleur. De plus, la réponse neurale liée à la douleur dans l'insula postérieure a diminué suite à l'exclusion sociale, alors qu'une augmentation du signal a été observée au niveau du cortex préfrontal médial dorsal et ventral, régions souvent impliquées dans le contrôle cognitif et la régulation des émotions. Enfin, la mise en œuvre de modèles à priori neurologiques multivariés, pour la douleur et le contrôle cognitif, a révélé une diminution du signal cérébral informatif sur la douleur physique lors de l'exclusion, mais aussi une augmentation du signal cérébral informatif sur le contrôle cognitif. Aucune des modulations observées pour les réponses comportementales, physiologiques et neuronales de la douleur ne s'est généralisée au cas du dégoût. Globalement, ces résultats montrent que l'exclusion sociale influence préférentiellement la sensibilité à la douleur, suggérant ainsi que l'interaction entre souffrance de nature physique et sociale est mieux interprétable en termes de codage spécifique à la douleur.

Enfin, le chapitre 5 décrit une expérience dans laquelle nous avons combiné les deux paradigmes des études précédentes, en remplaçant les stimulations thermiques et olfactives utilisées au chapitre 2 par des sessions de jeu Cyberball. Cela visait à tester si l'exclusion sociale est suffisamment similaire à la douleur thermique pour conduire à la même influence dans l'appréciation des expressions faciales. Malheureusement, nous n'avons trouvé aucune preuve en faveur de cette hypothèse. Au lieu de cela, l'exclusion sociale semblait faciliter spécifiquement la reconnaissance du dégoût, effet intéressant en soi, mais sans rapport avec la principale question expérimentale de cette thèse.

Dans l'ensemble, nos résultats confirment des travaux précurseurs selon lesquelles le comportement social partage certains niveaux de représentation avec sa propre expérience

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de la douleur et du dégoût. Cependant, il semble que différents processus sociaux sous- tendent différents composants sous-jacents à ces expériences somato-affectives: l'évaluation des états des autres partage un code supra-ordinal de désagrément, alors que l'exclusion sociale semble exploiter une représentation spécifique à la douleur, peut-être en codant des informations sur les propriétés de l'expérience douloureuse, et / ou mécanismes de sa régulation. En effet, les deux composantes spécifiques à la douleur et supra-ordinales semblent distinctes l'une de l'autre, car l'exclusion sociale n'influence pas l'évaluation de l'expression faciale de la même manière que la douleur thermique.

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Remerciements

Je souhaite exprimer toute ma gratitude envers le Professeur Corrado Corradi-Dell’Acqua pour sa supervision patiente et bienveillante tout au long du doctorat. Son esprit critique et sa passion pour la recherche scientifique m’ont inspirée et accompagnée pendant la réalisation de ce projet et également la rédaction de la thèse.

Je souhaite remercier les membres de l’examen oral et du jury présents lors de la soutenance publique de la thèse, les Professeurs Andrea Samson, Sophie Schwartz, Nicolas Silvestrini et Patrik Vuilleumier, pour le temps consacré à la lecture du manuscrit, ainsi que leurs encouragements et commentaires judicieux.

De plus, je souhaite remercier toutes les personnes qui ont été des enseignants importants pour moi : les Dr Sylvain Delplanque et Dr Gil Sharvit qui m’ont appris à utiliser l’olfactomètre, le gustomètre et la thermode et à analyser les données physiologiques; les Dr Eva Pool et Dr Kim Doell pour leur aide respective avec le preprocessing des données IRM et l’utilisation de l’ICA in FSL, ainsi qu’avec la tâche du Cyberball.

Je remercie également les Dr Christophe Mermoud et Dr Frédéric Grouiller pour leur aide sans faille avec les soucis techniques au BBL, ainsi que Bruno Bonnet et la Dr Laura Riontino pour m’avoir aidée avec beaucoup d’humour dans l’acquisition des données IRM.

Mes sincères remerciements vont aussi aux étudiants du Theory of Pain Laboratory et toutes les collaboratrices et tous les collaborateurs qui m’ont accompagnée pendant les expériences au laboratoire, ainsi que tous les participants qui y ont pris part.

De plus, je remercie ma collègue « jumelle » Giada Dirupo et tous mes compagnons de route, avec lesquels j’ai partagé des moments mémorables et instructifs pendant ces quatre ans de

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doctorat, durant les séminaires, les conférences nationales et internationales, les Journées de la science, à la nuit des musées ou simplement dans les couloirs du Campus Biotech.

Par ailleurs, je souhaite remercier mes amies et amis, et tout particulièrement ma famille, pour leur soutien précieux et leur fidèle confiance au cours de ma vie.

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Chapter 1 Theoretical Introduction

1.1 General purpose

In the last fifteen years, research in psychology and neuroscience showed that there is a very strong relationship between somatic states, such as pain and disgust, and social cognition.

This has been documented by empirical evidence obtained through two independent methodologies. At the behavioral level, several experiments demonstrated the ability of somatic states to induce changes in subsequent social tasks (and vice versa), whereas at the neural level neuroimaging techniques have revealed an overlap of activity patterns evoked by first-hand pain/disgust and social cognition. This evidence suggests that there is a common code between first-hand somatic states and our ability to interact with others.

However, we still do not know whether the nature of this relationship is state-specific, as embodied theories would suggest, and/or whether it is based on broader aspects that are shared between different states. For instance, we do not know whether physical pain specifically influences the evaluation of others' pain, whether physical disgust specifically influences the moral judgment of social behaviours, or whether common characteristics between those negative states (such as unpleasantness or arousal) influence in a broader fashion the evaluation of others’ emotional and social behaviours. Although embodied theories argue that witnessing suffering in others (e.g., pain, disgust), or reacting to social misconducts (ostracism or unfair behaviours) activates covertly affective and neural representations of first-hand somatic and affective experiences, such as pain and disgust, empirical evidence is grounded in measures which are often confounded between different states. More specifically, pain and disgust are multidimensional states, characterized by both state-specific and common components with other states. For instance, they share several

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features, such as an intrinsic unpleasantness, arousal, and evaluation of potential life-threats.

Furthermore, pain and disgust elicit similar facial muscles responses (e.g., corrugator supercilii) and neural activity in the same brain regions (e.g., anterior insula and anterior mid- cingulate cortex). Despite recent studies having partially dissociated the neural activity of pain and disgust in the insular and cingulate regions by employing sophisticated analyses, such as multivariate pattern analyses (MVPA), the low spatial resolution of current neuroimaging techniques might prevent such techniques from isolating the most subtle state-specific responses, thus making it difficult to assess whether these are re-enacted during social interactions. Thus, we do not know when we find an overlap of representations of first-hand pain or disgust and those of social cognition, whether this overlap taps a component that is state-specific or rather a component that is related to more general aspects.

Thus, this thesis aims at understanding whether the relationship between first-hand somatic experiences and social cognition is played on mechanisms that are state-specific, as suggested by embodied theories, and/or are related to more general aspects that are common between different states. To investigate this, we planned to match accurately first-hand pain and disgust for the level of unpleasantness and to systematically compare whether these influence (or are influenced by) different tasks of social cognition in a similar or dissociated fashion. We predicted that, if social cognition is grounded in sensory-specific representations of first-hand pain and disgust, then we should find modulations only for one of the two somatic-affective experiences. Alternatively, if social cognition underlies a supra-ordinal coding of unpleasantness, we should expect similar modulations to be associated with both kinds of somatic-affective experiences. For the purpose of the current dissertation, we chose two seminal social cognition paradigms, both at the core of hot debates involving embodied

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interpretations in neuroscience: processing of emotional facial expressions and social exclusion.

The purpose of this introductory chapter is to provide the reader with the theoretical background underlying theories of embodied social cognition (section 1.2), by focusing, in particular, on emotional facial processing (section 1.2.2.1) and social exclusion (section 1.2.2.2). Subsequently, it will discuss differential and shared aspects between first-hand pain and disgust, both at the theoretical level (section 1.3.1), and through the description of their behavioural/physiological (section 1.3.2), and neural responses (section 1.3.3). Based on the reviewed information, the last section (section 1.4.4) will describe in more detail the aim of the present dissertation, and will provide a schematic description of the rationale underlying the planned experiments.

1.2. The Evolution of Embodiment theories in social cognition

This section will review the theoretical advances in the research of embodied models in cognition (section 1.2.1). Subsequently, it will focus on embodied models in social cognition (section 1.2.2), in particular, in the processing of emotional facial expressions (section 1.2.2.1), and in social exclusion (section 1.2.2.2). It will discuss about definitions, and describe seminal models and discoveries that led to change of perspectives.

1.2.1. Embodiment theories in cognition

Embodied models argue that cognition is grounded in the representations of basal sensory, motor, and affective experiences. By embodiment theorists mean the relationship of the mind to bodily states, such as body postures, actions, and facial expressions, that arise when we interact with the world (Barsalou et al., 2003; de Vignemont & Singer, 2006; Gentsch et al., 2016). Embodied theories of cognition have been developed in contrast to the traditional cognitivism, mostly adopted by scientists from 1950s to 1980s. Cognitivists proposed the computational theory of mind, according to which the mind is viewed as a computer that

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processes information, and the body is considered exclusively as a peripheral input and output device. Thus, cognitive processes are seen as computational procedures that are based on symbolic and abstract mental representations of the experience (Fodor, 1975, 1983; Pylyshyn, 1984). Most importantly, these mental representations are considered as amodal re- descriptions of a given experience because they are stored in memory independently from the sensory, motor, or affective modalities that have characterized originally the experience itself. For instance, according to the cognitivist view, the format in which our brain stores the concept of “cello” is abstract , and independent of whether this is experienced through vision, audition, or action (for professional players). To describe the cognitivist approach, Hurley (2001) used the metaphor of “mental sandwich”, where sensory and motor states are the bread and cognitive processes are the meat. According to her, cognitivists move aside the bread and eat only the meat, as they study cognitive processes, but they neglect the body.

Conversely, embodied models of cognition conceive the mind as a system that rather supports the body in its sensory and motor functioning to interact successfully with the environment. Cognitive processes are not considered as abstract and amodal re-descriptions of the perceptual, motor, and affective states of a given experience, but as modality-specific representations of these states (Wilson, 2002). For instance, according to the embodied view, the format in which our brain stores the concept of “cello” relies on the sensory, motor, and even affective interactions that we had with the musical instrument. In other words, we store in our mind several modality-specific representations, such as a “visual cello”, an “auditory cello”, a “motor cello”, and so on (Barsalou et al., 2003).

Several embodied models followed one another, by highlighting the importance of perceptual and motor aspects in cognitive processes. On one hand, they inherit the primacy of perception by phenomenology. Interestingly, the phenomenologist Merleau-Ponty (1945)

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proposed to overcome the mind-body dualism and introduced the notion of the corporeity of perception, according to which our bodies are the perceivers in the interaction with the environment. On the other hand, these models inherit the importance of motor aspects by the American pragmatism and the ecological psychology of Gibson. According to pragmatists, concepts are not mere representations of objects, but rather the representations of functions and practical uses of these objects (Mead, 1934). For instance, Mead proposed that the concept of “horse” does not correspond to the representations of the animal, but rather to those of potential interactions with the animal (e.g., how we approach him or climb on to him - Mead, 1934). Similarly, embodied models of cognition inherit the notion of affordance from the ecological psychology elaborated by Gibson, according to which perception guides and supports actions, enabling the individual to extract useful and functional information to interact with the environment (Gibson, 1973).

During the last thirty years, numerous findings in psychology and neuroscience have been interpreted in terms of embodiment, and cognition has been labeled as “situated”,

“grounded”, “embodied”, and “enacted”. Although these labels have been used to generically highlight the crucial role of the body’s interactions with the world in cognitive processes in contrast with the classic cognitivism, they claimed slightly different assumptions. Here, I provide a brief clarification of the meaning of these labels and their respective assumptions.

1) Proponents of situated cognition argued that the environment plays a crucial role in shaping cognitive processes. Cognition is linked to the interaction with the world, and cannot be separated from the physical and socio-cultural contexts, or situation in which it has been acquired. According to situativity theorists, for instance, learning happens in and

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from interacting with others or the environment (Chiel & Beer, 1997; van Gelder & Clark, 1998).

2) Grounded cognition refers more specifically to the “ground”, that is our senses, and less to the “body”. According to Barsalou (2008), modality-specific representations of the sensory and motor states acquired with experience can be re-enacted for later cognitive use. Importantly, these representations are deeply rooted in our sense organs, and are quite independent from the representations of our body, although they are closely related to them.

3) Goldman and de Vignemont (2009) went back to the importance of the notion embodied and its relation to the body. According to them, mental processes are represented under the bodily format not only for sensory, motor, and affective functions, but also for some social cognitive functions, such as emotion contagion, empathy, and so on. For instance, in empathy, perceiving or imagining another person suffering elicits suffering in oneself.

In both cases, the feeling of suffering involves a representation in body format.

4) Enacted cognition stated that cognitive processes arise through an active mutual interaction between the sensorimotor capacities of an organism and his environment.

Here, perception must be understood as an explorative activity, rather than as a passive one. According to enactivists, for example, we cannot recognize and classify objects by exploring them exclusively through our sense of touch, without using also our motor actions (O’Regan & Noë, 2001).

Despite the fact that these labels highlighted different components that constitute the foundations of cognitive functions, such as in situ interactions for situated cognition, sensory components for grounded cognition, body format for embodied cognition, and sensorimotor

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components for enacted cognition, all of them hold that the bodily states play a crucial role in the mind.

At the end of the twentieth century, research made great efforts to understand the neural basis of behaviour and cognition. Importantly, in 1989, Damasio elaborated the convergence-divergence zones (CDZ) theory to explain the neural mechanisms of memory retrieval. He suggested that CDZ are a neural network organized in multiple hierarchical levels.

The convergent projections feedforward the information from the sites whose activity is recorded (e.g., early sensory cortices, and motor cortex), whereas the divergent pathways feedback the information from higher level areas to former sensory and motor levels (Damasio, 1989). In addition, this theory proposed that convergence zones capture the modality-specific patterns of information and merge them into amodal codes related to the representations across modalities, by establishing associative relationship between them.

While, divergence zones reproduce the original modality-specific patterns from the amodal code. Critically, Barsalou (Barsalou, 1999; Simmons & Barsalou, 2003) extended the CDZ theory to argue that a given experience is translated in terms of modality-specific re- enactments of its sensory, motor and, affective components. Hence, in his seminal theory of perceptual symbol systems, he explained that the process of re-enactment is characterized by two phases: 1) the storage of the modality-specific states arisen during the experience, and 2) the partial re-enactment of these states on later occasions. In other words, coming back to the former example of the concept of “cello”, when we see, listen to, or play this musical instrument, first we partially store the bodily states that arise during the interaction with it.

Second, when we will talk, think about, or remember this concept, the stored states will be partially simulated. This approach does not mean that bodily states will manifest overtly, but

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that they will be simulated covertly, with cerebral (and spinal) activations similar to those observed during the original bodily states (Barsalou et al., 2003).

A schematic illustration (see Figure 1.1) shows how the modality-specific information is captured (A) and re-enacted (B). For instance, during the perception of a face, the visual information reaches the brain through sensory channels and neurons fire in feature maps organized topographically to code the pattern of the specific sensory representation.

Subsequently, conjunctive neurons in an association area capture a particular pattern related to the sensory representation (i.e., convergence). During the re-enactment, in absence of bottom-up stimulation, conjunctive neurons in the association area fire to partially reactivate the earlier sensory representation, and neurons in feature maps fire to re-enact the earlier sensory representation (i.e., divergence). For example, when we remember the face of a person, conjunctive neurons can partially reactivate the visual pattern activity while they were perceiving it. Similarly, when we imagine playing the cello, conjunctive neurons partially activate the motor patterns that produced those movements. However, re-enactments are partial recreations of experience and, thus, they are potentially inaccurate, unconscious, and influenced by biases and errors (Barsalou, 1999; Barsalou et al., 2003).

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Figure 1.1: Schematic representation of the capture (A) and re-enactment (B) of the modality-specific information proposed by Damasio (1989) and Barsalou (1999; Barsalou et al., 2003, p. 65).

Furthermore, in the theory of perceptual symbol systems, Barsalou (1999) proposed that two constructs called simulators and simulations play a role in the re-enactment process.

Essentially as concepts, simulators capture specific contents of a given category across modalities and integrate them into a multimodal representation stored in memory. Later, they can re-activate specific contents of the category called simulations. For example, every time the simulator face encounters an exemplar of the category face, neurons activate a neural pattern in feature maps. Subsequently, overlapping conjunctive neurons capture the patterns of all exemplars of faces encountered and link the features across different faces to each other in convergence-divergence zones to establish a multimodal representation of the category face. Then, the simulator face, for instance, might produce simulations by re-enacting a smiling face, on a particular situation, whereas on others it might re-enact an angry or sad face. Figure 1.2 provides a schematic explanation of the capture (A) and re-enactment (B)

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processes operated by the system of simulators and simulations (Barsalou, 1999). Re- enactment processes can be influenced by many factors, such as genetics, culture, language development, and so on (Barsalou et al., 2003).

Figure 1.2: Schematic illustration of processes of capture (A) and re-enactment (B) operated by the system of simulators and simulations (Barsalou, 1999; Barsalou et al., 2003 p. 68).

1.2.2 Embodiment theories in social cognition

In the last fifteen years, research in psychology and neuroscience provided empirical evidence to explain the cognitive and neural processes underlying our ability to interact with others and understand their actions, intentions, and feelings. In fact, intersubjective relations not only

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denote the essential social trait of the human mind, but they offer an opportunity to understand how the human mind develops and works. Again phenomenological traditions provided relevant insights that influenced the way of thinking about the body’s role in social cognition. Some phenomenologists used the analysis of the body to articulate the foundations of intersubjectivity in contrast to the individual solipsistic view, according to which only one’s own mind exists and other’s mental states are unknown. For instance, Husserl emphasized the relationship between the self and others’ bodies in intersubjective interactions. He pointed out that we do not perceive others’ bodies as mere physical objects, but as living bodies that have posture, execute actions, and with whom we can interact (Husserl, 1989).

According to Merleau-Ponty, human relationships are grounded in the body. “Other minds are given to us only as incarnate, as belonging to faces and gestures” (Merleau-Ponty, 1964, p.

16). He argued that other’s mental activities are not separated from others’ bodies in a dualistic way, but they both participate in interactive processes by talking to each other. Thus, his notion of intercorporeity can be considered as a basis of embodied accounts related to the human ability to interact with and understand others.

According to these accounts, we can understand others by perceiving and simulating their gestures, body-postures and facial expressions. During infancy we learn how to move, engage in relationships, and express our emotions from interacting and observing how other people move, engage in relationships, and express their emotions. For example, if a child smiles at her mother, she will smile back. If someone turns his gaze towards a certain direction, we will look toward that direction. These embodied interactions have been described in terms of perception-action loops that occur between oneself and others. In other words, perceiving the actions of another person activates the same potential actions in the perceiver and vice versa (Prinz, 1990). In the field of action understanding, Prinz (1990)

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elaborated the common coding theory, according to which perceptions and actions have shared representations because they rely on common neural substrates. This theory claims that sensorimotor properties of neurons would lead to activating simultaneously perceptions and actions associated with the same event.

The discovery of the mirror neurons in animal research in the 1990s captured great attention in psychology and neuroscience because they have been considered as a neural evidence of these perception–action loops between oneself and others. In fact, mirror neurons are active when monkeys execute actions as well as when they observe the same actions executed by someone else (di Pellegrino et al., 1992; Rizzolatti et al., 1996). This discovery inspired a line of research in social neuroscience suggesting that in humans the neural mechanisms underlying imitation and understanding of other’s behaviours rely on shared neural representations of both perceptual and motor processes. In the light of embodied models of cognition reviewed above, observing other’s actions re-enacts automatically the representations of the same actions in the brain of the observer, as if he or she executed those actions in front of the mirror (Decety & Grèzes, 2006; Gallese, 2007;

Gallese et al., 2004; Iacoboni & Mazziotta, 2007).

Furthermore, Gallese and Goldman (1998) linked the discovery of mirror neurons to their simulation theory, suggesting that the ability to share other’s mental states depends on shared embodied simulations between the self and other. Importantly, they explained that we understand actions, goals, and intentions of other people by taking our own mind as a model for other people’s minds. In other words, we automatically simulate our actions and intentions, by putting ourselves in others’ shoes (Gallese, 2003; Gallese & Goldman, 1998).

Critically, Gallese (2003) underlined that self-simulations are automatic and unconscious and, thus, they do not require any cognitive deduction of what actions and feelings of other people

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mean. Therefore, the simulation theory is in contrast with the theory theory that, conversely, argues that the ability to understand others is based on deliberate theoretical inferences that try to predict and explain other’s behaviours (Ratcliffe, 2006), and other’s thoughts and points of view (mostly known as theory of mind - Leiberg & Anders, 2006). Finally, another theory called the interaction theory emphasizes the primary role of embodied interactive relations in the comprehension of others’ minds and feelings. It argues that we understand others’

intentions and emotions by simply interacting and perceiving their bodily postures, facial expressions, and actions, not by inferring any belief or meaning of their behaviours (Gallagher, 2001, 2004). For example, when we see a happy face, we do not have to read the mind of the person for understanding his or her feeling. Happiness is already expressed on the face.

1.2.2.1 Embodiment theories in the processing of emotional facial expressions

Crucially, social neuroscience extended the investigation of shared neural networks between the first-hand experience and observation in others from the domain of actions (Rizzolatti et al., 2001) into those of sensations (Keysers et al., 2004), and emotions (Carr et al., 2003; Leslie et al., 2004; Wicker et al., 2003). A seminal paper of Preston and de Waal in 2002 suggested that when we witness an emotional state of another individual we activate automatically the representation of the same state in ourselves (Preston & de Waal, 2002). This mechanism was used as model for empathy, mostly defined as the conscious ability to recognize and share the same feelings and emotions of others (de Vignemont & Singer, 2006).

A large number of studies compared brain responses to the experience of a given emotion in oneself with those evoked by directly observing or imaging the same emotion in others through several neuroimaging techniques, such as functional magnetic resonance imaging (fMRI - Botvinick et al., 2005; Gu & Han, 2007; Jackson et al., 2005; Morrison et al., 2007; Saarela et al., 2007; Singer et al., 2004), electrophysiological recordings (Bufalari et al.,

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2007; Cheng et al., 2008; Han et al., 2008), transcranial magnetic stimulation (TMS - Avenanti et al., 2005), and laser-evoked potential (Valeriani et al., 2008). The majority of these studies investigated empathy for pain and supported the model of Preston and de Waal by finding similarities of cortical activations between both felt and seen pain in anterior mid-cingulate cortex (also termed dorsal anterior cingulate cortex; aMCC/dACC) and in anterior insula (AI - see Figure 1.3; Jackson et al., 2005; Lamm et al., 2011; Singer et al., 2004, for meta-analyses, see Fan et al., 2011; Lamm et al., 2011), two regions known to be responsible for the self- experience of pain (Apkarian et al., 2005; Derbyshire, 2000; Peyron et al., 1999).

Figure 1.3: Shared and distinct activations between self- and other pain found by the meta-analysis of Lamm et al., 2011. Common activations in AI, aMCC, precuneus and thalamus are color-coded in red and displayed at the voxel-wise conjunction threshold P=0.0001, uncorrected, whereas distinct activations for self-pain in posterior insula (PI), S1, and aMCC are color-coded in green and displayed at a threshold of P(FWE)=0.01, k=20.

Remarkably, it has been also found that exclusively the direct observation of limbs or body parts of people in painful situations was associated with strong activations in the posterior

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insula (Corradi-Dell’Acqua et al., 2011) and primary/secondary somatosensory cortices (S1 and S2) implied to underlie the sensory-discriminative components of the painful experience (Lamm et al., 2011). This has been interpreted consistently with the fact that observing others’

injuries allows a more direct and immediate mapping between self and others, as opposed to being informed about the same event through abstract associations.

In addition to neuroimaging evidence, a few studies showed that analgesic manipulations acting on the opioid system can reduce not only the physical and emotional sensitivity towards one's own suffering, but also towards that of others (Braboszcz et al., 2017;

Rütgen et al., 2015a; Rütgen et al., 2015b). These findings indicate that self-nociception is crucial in empathy for pain and presumably it should recruit a neural network that is partly similar to that activated by first-hand experiences (Bastiaansen et al., 2009; Caruana et al., 2011; Goldman & de Vignemont, 2009).

Even more interestingly, key role of aMCC (extending to the supplementary motor area) and AI (extending to the inferior frontal gyrus) in empathy have been provided by studies investigating also different affective experiences other than pain (for meta-analysis, see Bzdok et al., 2012). More specifically, three recent meta-analyses compared systematically studies on empathy toward physical pain and other negative emotional states, leading to overlapping effects in these two regions (Ding et al., 2020; Kogler et al., 2020; Timmers et al., 2018, see Figure 1.4).

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Figure 1.4: Convergence of brain activations for empathy for pain and for other negative states in AI, aMCC, SMA, and IFG, provided by the meta-analysis of Timmers et al., 2018.

Furthermore, a few studies implemented more sophisticated analyses, such as the multivariate pattern analysis (MVPA), and they found similar distributed patterns of neural activity in AI, middle-posterior insula and aMCC between felt and seen pain (Corradi- Dell’Acqua et al., 2011; Corradi-Dell’Acqua et al., 2016; Qiao-Tasserit et al., 2018; Wagner et al., 2019; O’Connell et al., 2019, but see Krishnan et al., 2016), disgust, unfairness (Corradi- Dell'Acqua et al., 2016), and fearful anticipation of pain (O’Connell et al., 2019).

Taken together, these findings are in line with the predictions of embodied theories, proposing that when we empathize with other’s emotional states we re-enact the representation of the same emotional states in ourselves, by activating the brain network engaged for first-hand experience of the same emotions. Moreover, it is interesting to notice that this shared neural activation has been suggested to play a role not only in tasks asking to explicitly empathize with others, but also in those where participants had to simply observe others’ emotional faces. In fact, it exists a wide literature in psychology and neuroscience on emotional facial processing that supports embodied theories. This line of research points out

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that perceiving emotions on the face of another person implies the embodiment of the same emotions in the perceiver, as if this person was in front of the mirror looking at his/her own face (Decety & Grèzes, 2006; Gallese, 2007; Gallese et al., 2004; Iacoboni & Mazziotta, 2007).

Behavioral studies showed that observers imitated spontaneously facial expressions and gestures seen in others (Iacoboni, 2009; for review, see Wood et al., 2016), and felt the corresponding emotions (Bandura & Rosenthal, 1966; Berger, 1962). Interestingly, it has been found that, after one second of exposure to emotional faces, electromyography (EMG) recorded the activity of facial muscles congruent to those contracted in the observed faces (Dimberg et al., 2000). This tendency to mimic others’ facial expressions is termed facial mimicry and it is held to occur unintentionally and unconsciously (Dimberg et al., 2000).

More interestingly, it has been suggested that mimicking faces plays a causal role in the processing of facial expressions. In particular, several studies showed that manipulating specific facial muscles on either the lower or the upper half of the face, through the biting-a- pen procedure, hindered the recognition of facial expressions that involve the same muscles (Oberman et al., 2007; Ponari et al., 2012). In addition, Borgomaneri et al. (2020) blocked facial mimicry and asked participants to perform emotion and gender recognition tasks. In line with previous studies, they observed that mimicry manipulation impaired the recognition of facial and, even, bodily expressions, but not that of the actor’s gender. Therefore, these authors argued that facial mimicry is not a mere reproduction of motor expressions, but an internal simulation of the emotions observed in others (Borgomaneri et al., 2020). Further studies reported the impact of facial mimicry interference also on brain responses to others’ emotions (Davis et al., 2017; Hennenlotter et al., 2009). For instance, Hennenlotter et al. (2009) recorded the functional brain responses to imitation of facial expressions after having induced in participants temporal denervation of frown muscles, through botulinum toxin (BTX)

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injections, and compared them with those relative to the control condition in absence of BTX treatment. They observed that the imitation of angry faces was associated with reduced activity of the left amygdala and its lower functional connectivity with brain stem, that is known to be involved in autonomic responses to emotions, such as heart rate and skin conductance (Hennenlotter et al., 2009). Consistently, another study recorded electroencephalography (EEG) and showed that mimicry interference influenced event- related potentials by eliciting a negative-going waveform that peaks 400 ms after the presentation of a face. As amplitudes with such timing have been interpreted as the result of more demanding processing of semantic information (Paulmann & Pell, 2009), authors argued that disrupting facial mimicry might make more difficult to understand the emotional content of faces (Davis et al., 2017).

Hence, in line with the studies that showed the activation of the mirror-neuron system in oneself during the observation of actions in others (di Pellegrino et al., 1992; Rizzolatti et al., 1996; Rizzolatti et al., 2001), it has been found that the perception of pain and other emotional facial expressions in others re-enacts self-bodily states in relation to the emotions observed, such as automatic imitations of others’ facial expressions and the recruitment of premotor areas involved in performing similar facial movements (motor simulation), such as premotor cortex (Carr et al., 2003; Hennenlotter et al., 2005), as well as areas involved in experiencing the same affective state (emotional simulation), such as AI and frontal operculum (FO - Botvinick et al., 2005; Jabbi et al., 2007; Wicker et al., 2003). For example, when people watched videos displaying facial expressions of disgust they activated AI involved in the direct experience of disgust evoked by disgusting odours and tastes (see Figure 1.5 - Jabbi et al., 2008; Wicker et al., 2003).

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Figure 1.5: Overlap (white) of brain activation between the brain response to the observation (blue) of faces expressing disgust and the exposure (red) to disgusting odours (Wicker et al., 2003).

Importantly, Jabbi and Keysers (2008) found enhanced functional connectivity between the premotor cortex and AI/FO during the observation of emotional compared to neutral faces.

More importantly, by modeling the direction of the connectivity, they argued that it was the activity in the premotor cortex that influenced AI/FO, and not the opposite, thus supporting the hypothesis that motor simulation has an impact on emotional processing (Jabbi & Keysers, 2008).

Furthermore, a large number of studies has proven that experiencing a particular emotion can affect the perception and appraisal of facial expressions of the same emotion in others and vice versa. For instance, watching movies inducing happiness, sadness, or fear enhanced participants’ sensitivity towards facial expressions of the congruent state (Niedenthal et al., 2001; Niedenthal et al., 2000; Qiao-Tasserit et al., 2017). Niedenthal and colleagues (2000) used computerized happy and sad faces that gradually became neutral and asked participants to detect the offset of the initial emotion. They found a congruent effect.

Participants in happy states saw happy expressions lasting longer on the face and, thus,

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detected at later frames when happy faces became neutral than participants in sad states.

Interestingly, Qiao-Tasserit and colleagues (2017) found this emotion-congruent effect on the interpretation of ambiguous facial expressions. They exposed participants to happy, fearful and neutral movies and asked them to perform a forced-choice emotion classification task with morphed faces, ranging from fear to happiness. They observed that induced fearful states increased participants’ propensity to interpret ambiguous faces as more fearful than those relative to induced neutral or positive states.

Consistently, in the domain of pain, several studies revealed that the observation of pain in others can increase the perception of pain felt on oneself and vice versa (Gerdes et al., 2012; Mailhot et al., 2012; Reicherts et al., 2013 ; for review, see Wieser et al., 2014). For example, Mailhot et al. (2012) exposed participants to dynamic clips of painful and neutral facial expressions, and subsequently they administered to them painful shock stimulations and asked to report self-pain ratings. Results showed that after being exposed to painful faces participants rated painful stimulations as more unpleasant than those after being exposed to neutral facial expressions (Mailhot et al., 2012). Critically, these authors recorded the activity of the muscle called corrugator supercilii of participants following the painful stimulation.

They observed higher muscle responses to painful stimulations after the exposure to painful faces compared to the responses after the exposure to neutral faces. Therefore, these results seem to be in line with studies reporting automatic imitation responses following the observation of emotions in others (Dimberg, 1982; Dimberg et al., 2000).

Crucially, a few studies have revealed also the reverse effect. For instance, Gerdes and colleagues (2012) in their study induced pain through pressure stimulations and measured its impact on the processing of angry and happy faces. They asked participants to rate the valence and arousal of facial expressions, and to contract compatible and incompatible facial muscles

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in response to faces. In particular, in the compatible condition, participants had to react to happy faces with the muscle called zygomaticus major (used when we smile), and to angry faces with the corrugator supercilii, (used when we frown). Whereas, in the incompatible condition, the instructions were the opposite. Results showed that painful stimulations (relative to non-painful) were associated with fewer errors of the corrugator supercilii, in the incompatible condition, and delayed contractions of both muscles exclusively in response to happy faces. Whereas, pain did not modulate muscle responses to angry faces nor the valence and arousal ratings of both faces. Thus, the authors interpreted these findings suggesting that pain affected selectively the automatic processing of emotional happy faces. (Gerdes et al., 2012). Consistently, one study investigated the mutual effect of first-hand and vicarious pain, by asking participants to rate the arousal and valence of pain, fear, joy and neutral dynamic facial expressions while they were receiving a painful (vs non-painful) thermal stimulation (Reicherts et al., 2013). Results revealed that facial expressions of pain and fear were rated as more arousing while participants received painful stimulations compared to non-painful stimulations. Self-pain ratings were augmented after exposure to painful faces compared to all other faces. In addition, authors recorded responses of facial muscles to painful stimulations and found that the activities of orbicularis oculi and zygomaticus muscles were higher than those relative to control conditions and correlated positively with subjective pain ratings.

Taken together, these reviewed behavioral and neuroimaging studies support embodied theories of social cognition, suggesting that the observation of others’ facial emotional expressions is partly instantiated in neural structures and, thus, in representations of similar facial expressions and feelings in the perceiver (Bastiaansen et al., 2009; Caruana et al., 2011; Goldman & de Vignemont, 2009).More importantly, it has been shown that motor

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and emotional self-simulations of others’ emotions can serve adaptive purposes, by improving emotion recognition. For instance, Chartrand and Bargh (1999) considered facial mimicry and behavioral coordination as the “social glue”, and they provided empirical evidence that they play adaptive roles in social interactions, by facilitating interpersonal bonding, greater liking between people and social understanding (Chartrand & Bargh, 1999).

1.2.2.2 Embodiment theories in social exclusion

We humans are inherently social. In real life, we engage ourselves in social interactions and appreciate the value of making and maintaining social connections. Even in situations of forced social isolation, due to the restrictions linked to Covid-19, we still continue to engage ourselves in many social virtual interactions, by overscheduling our lives on virtual platforms for having meetings, sharing dinners, celebrating birthdays, and so on (Timsit, 2020).

Undoubtedly, social behaviour is important for our health and survival. It constitutes a dominant force that shapes physiological and neural activities, and, thus, how we behave and think (Cacioppo et al., 2000). In the 1990s, Dunbar proposed the “social brain hypothesis” as an explanation of brains unusually large for body size observed in primates compared to all other vertebrates. He showed that in primates the size of neocortex correlates positively with the size of social groups. Thus, evolved large brains may be driven by processing the cognitive demands associated with living in large and complex social groups (Dunbar, 2009; 1998). Most importantly, Dunbar claimed that these cognitive mechanisms are the precursors of the evolution of social cognition because they are responsible of strong bonded social groups, in which individuals interact each other more frequently and come to mutual aid against other group members (Dunbar, 2009). In fact, positive and long lasting human relationships are associated with mental and physical health (Cacioppo et al., 2000; Jaremka et al., 2011).

Whereas, being rejected by others and losing a loved one are associated with distress,

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negative mood, and suffering (Jaremka et al., 2011; Onoda et al., 2010). Interestingly, we describe these experiences of social disconnection as one of the most upsetting, devastating, or even painful experiences that we had ever to endure, even though there was no tissue damage or potential physical hurt (Jaremka et al., 2011). We use metaphors that usually we refer to physical pain, such as « heartbreak », « hurt feelings ». This phenomenon is not only visible in English language, but also in many other languages around the world (MacDonald &

Leary, 2005). Is it only a mere linguistic coincidence or is there something more underneath?

In the last fifteen years, research in psychology and neuroscience has suggested different views on how the human brain represents the break of social bonds. Several scholars tested the metaphors of « heartbreak » and « hurt feelings » by investigating the relationship between social exclusion and physical pain (Eisenberger et al., 2003; Kross et al., 2011;

Novembre et al., 2015). Experimentally, they induced social exclusion through several paradigms. Some studies showed images of disapproving faces to participants (Kross et al., 2007), or pictures of participant's ex-partners with whom the romantic relationship broke badly (Kross et al., 2011). Others used the “future life” paradigm, through which participants received a negative feedback regarding their future social relationships resulting from the scores obtained in fake personality tests (DeWall & Baumeister, 2006). However, the paradigm mostly used is the cyberball game provided by Williams (2000). This task asks participants to play at a virtual ball-tossing game with other players that include (inclusion condition) or exclude (exclusion condition) them in the game. In reality, the other players are confederates and the game is controlled by a computer. Several studies found overlapping brain activations between social exclusion and physical pain in AI and aMCC (Eisenberger et al., 2003; Kross et al., 2011; Novembre et al., 2015). Consistent with the models of empathy for pain described above, the activations of AI and aMCC have been considered as re-enactments of the affective

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properties of physical pain. Interestingly, two of these studies used a within-subject design to compare suffering of physical and social nature, and they reported overlapping activations also for S2 and posterior insula (PI - Kross et al., 2011; Novembre et al., 2015, see Figure 1.6), regions held to be implicated in sensory properties of physical pain (Davis, 2000; Peyron et al., 2000).

Figure 1.6: Brain overlap between social rejection (Ex-partner > Friend) and physical pain (Hot >

Warm) in AI, dACC/aMCC, thalamus, and S2. Bar graphs demonstrate the β-values associated with social rejection and physical pain did not differ (all two-tailed paired sample t statistics < 1.75, all P values > 0.09 - Kross et al, 2011).

Remarkably, the subjective distress felt by participants during the exclusion correlated positively with the neural activity of AI and aMCC (DeWall et al., 2012; Eisenberger et al., 2003;

Krill & Platek, 2009; Masten et al., 2011, 2012; Onoda et al., 2009). Whereas, it correlated negatively with the neural activity in the right ventral prefrontal cortex (RVPFC - Eisenberger et al., 2003), a region known to be involved in the regulation or inhibition of pain distress and negative affect (Hariri et al., 2000). The authors of these studies interpreted their results suggesting that the greater was the activity in AI and aMCC, the more participants felt distressed by social exclusion, whereas the greater was the activation in RVPFC, the less participants felt distressed by social exclusion.

Beyond unpleasantness: the interplay between social cognition and the somatic-affective states of pain and disgust

Thesis

Reference

Beyond unpleasantness: the interplay between social cognition and the somatic-affective states of pain and disgust

BEYOND UNPLEASANTNESS. THE INTERPLAY BETWEEN SOCIAL COGNITION AND THE SOMATIC-AFFECTIVE STATES

OF PAIN AND DISGUST

Lia ANTICO

To the women of my life,

mum Mafalda and grandma Iolanda

Placer le rêve et l’émotion au cœur de l’aventure scientifique

Abstract

Résumé

Remerciements

Table of contents

Chapter 1

Theoretical Introduction