A MULTIPLE REPRESENTATIONS MODEL OF THE HUMAN MIRROR NEURON SYSTEM FOR LEARNED ACTION IMITATION

The human mirror neuron system (MNS) is a fundamental sensorimotor system that plays a critical role in action observation and imitation. Despite a large body of experimental and theoretical MNS studies, the visuospatial transformation between the observed and the imitated actions has received very limited attention. Therefore, this work proposes a neurobiologically plausible MNS model, which examines the dynamics between the fronto-parietal mirror system and the parietal visuospatial transformation system during action observation and imitation. The fronto-parietal network is composed of the inferior frontal gyrus (IFG) and the inferior parietal lobule (IPL), which are postulated to generate the neural commands and the predictions for its sensorimotor consequences, respectively. The parietal regions identified as the superior parietal lobule (SPL) and the intraparietal sulcus (IPS) are postulated to encode the visuospatial transformation for enabling view-independent representations of the observed action. The middle temporal region is postulated to provide the view-dependent representations such as direction and velocity of the observed action. In this study, the SPL/IPS, IFG, and IPL are modeled with artificial neural networks to simulate the neural mechanisms underlying action imitation. The results reveal that this neural model can replicate relevant behavioral and neurophysiological findings obtained from previous action imitation studies. Specifically, the imitator can replicate the observed actions independently of the spatial relationships with the demonstrator while generating similar synthetic functional magnetic resonance imaging blood oxygenation level-dependent responses in the IFG for both action observation and execution. Moreover, the SPL/IPS can provide view-independent visual representations through mental transformation for which the response time monotonically increases as the rotation angle augments. Furthermore, the simulated neural activities reveal the emergence of both view-independent and view-dependent neural populations in the IFG. As a whole, this work suggests computational mechanisms by which visuospatial transformation processes would subserve the MNS for action observation and imitation independently of the differences in anthropometry, distance, and viewpoint between the demonstrator and the imitator

A multimodal investigation of matching mechanisms in automatic imitation

In recent years, research on imitation focused on investigating the underlying neural mechanisms; to this aim simple paradigms were developed to experimentally investigate the phenomenon. Following the natural tendency of humans to mimic gestures and postures of their conspecifics, paradigms of automatic imitation are nowadays widely used in the field. The main aim of my dissertation is to investigate how imitation occurs using an automatic imitation paradigm, in particular focusing on the matching processes that are required to map model and performers actions.The dissertation contains six chapters. In chapter 1, I will provide a brief background of the current theoretical accounts of imitation and of the concepts of automatic imitation and compatibility effects. I will particularly focus on the questions concerning automatic imitation that are still to be fully addressed, particularly those related to the distinction of imitative and spatial compatibility. I will also address the neuroimaging and neuropsychological literature on the neural correlates of imitation. In chapter 2, I will present a neuroimaging study I carried out to investigate the imitation components. Throughout all the studies of this thesis, we used a simple automatic imitation paradigm that is suitable to differentiate between the spatial compatibility and the imitative compatibility, due to the anatomical correspondence between model and performer. Results of the first study showed that the parietal opercula are active anytime the anatomical correspondence between model and performer is present. Hence, in chapter 3 I will present a study in which double-pulse TMS was used to investigate the role of the parietal opercula in automatic imitation, and in particular in coding the imitative compatibility. Results showed that when the activity in the parietal opercula is interfered by TMS, the imitative compatibility effect disappears. In the second part of my thesis I have investigated the factors that can interact with and modulate imitative behaviors. Chapter 4 contains an fMRI study in which the role of the model in imitation is investigated. Using a simplified version of the automatic imitation paradigm, I found that the fronto-parietal network, usually associated to imitation, is more active when participants perform actions that are compatible with those performed by a human model than by a non biological model. Moreover, in this study I have also investigated how different emotional contexts can influence the automatic tendency to imitate. The results showed that the activation of the fronto-parietal network is suppressed by emotional context, such as an angry face, that does not promote affiliative tendencies. In chapter 5 I will describe a neuropsychological study on brain damaged patients. Associations and dissociations between automatic imitation and action imitation were investigated, to analyze the differences between the two types of imitation. Moreover, the role of putative body representations in imitation and whether these body representations are needed for imitation has been investigated. Lastly, in chapter 6 I will wrap up the main results of my dissertation and I will argue that I was able to provide evidence that in automatic imitation an anatomical matching operates between the model and the performer, and that this is sustained by the parietal opercula. In addition I clarified the importance of the model, showing that the activity of fronto-parietal regions supporting imitative behaviors is modulated by model identity

Motion as manipulation: Implementation of motion and force analogies by event-file binding and action planning\ud

Tool improvisation analogies are a special case of motion and force analogies that appear to be implemented pre-conceptually, in many species, by event-file binding and action planning. A detailed reconstruction of the analogical reasoning steps involved in Rutherford's and Bohr's development of the first quantized-orbit model of atomic structure is used to show that human motion and force analogies generally can be implemented by the event-file binding and action planning mechanism. Predictions that distinguish this model from competing concept-level models of analogy are discussed, available data pertaining to them are reviewed, and further experimental tests are proposed

The Tie between Action and Language Is in Our Imagination

In this thesis, the embodied cognition proposal that action words are directly and automatically mapped into the perceiver\u2019s sensorimotor system, and understood via motor simulation, has been put under the lenses of neuropsychology, psychophysics, transcranial magnetic stimulation (TMS), and functional magnetic resonance imaging (fMRI) investigation. The objective was to establish whether the tie between language understanding and motor simulation is necessary for the former to be effective, to the extent that a virtual identity can be recognized between action and language systems..

The neuroanatomy of pictorial reasoning in autism

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 163-177).Individuals with autism present with a constellation of social, behavioral, and cognitive symptoms. A striking characteristic is the contrast between their language and visual processing abilities. The work in this thesis combines behavioral, functional MRI, and diffusion tensor imaging methods to examine the neurobiological basis of the discrepancy between linguistic and visuospatial skills in autistic cognition. A pictorial reasoning task, designed to manipulate the degree to which language vs. visuospatial abilities may be differentially engaged in solving picture puzzles, was administered under three conditions: visuospatial, semantic and a hybrid visuospatial-cum-semantic condition. Whereas participants with Asperger's syndrome and typically developing controls (CTRL) were found to exhibit similar performance profiles, high-functioning individuals with autism (HFA) differed from these two groups: they were least efficient on the semantic condition and appeared to benefit from and favor the use of visuospatial mediation in problem solving. Results from functional MRI revealed a pattern of decreased activation in fronto-temporal language areas, and an increased reliance on posterior brain regions in the parietal and ventral temporal lobes in HFA, supporting the earlier behavioral findings. Specifically, the inferior frontal gyrus appeared to play an important role in verbal mediation and semantic integration in CTRL, whereas HFA relied more extensively on inferior and ventral regions of the temporal lobe, in keeping with a cognitive preference for visual strategies.(cont.) An examination of white matter integrity yielded a similar finding in the relationship between structural neuroanatomy and cognitive profile, such that connectivity patterns were related to the semantic mediation difficulties and visual processing preference in the HFA group: tracts relevant for semantic processing in CTRL were disrupted in HFA along the superior longitudinal fasciculus and in the frontal lobe, whereas parietal and inferior temporal white matter supporting visuospatial processing were intact in HFA The results suggest that performance in high functioning autism may be related to deficits in frontal cortex connectivity, in favor of visualization strategies in higher-level cognition. The findings appear to support the use of visuospatial vs. linguistic tasks to differentiate between potential subtypes on the autism spectrum.by Chérif P. Sahyoun.Ph.D

Social cognition and behavioral responses in kinematic interactions

As social beings, humans are constantly probed to infer intentions from verbal and non- verbal communication and to react according to the kinematic signals of other people. In this way, social cognition is tightly bound to our ability to perceive, predict and perform socially relevant actions. Being characterized by impairments in social interactions, in- dividuals with autism spectrum disorder (ASD) demonstrate insensitivity to predictive social stimuli as well as abnormal kinematic control both on the behavioral and the brain level. Underlining the severe consequences of impaired social interactive capabilities, autistic individuals are at high risk of social exclusion and concomitant mental health issues. Therefore, the investigation of the behavioral and brain responses to social ac- tions might yield valuable insights into the fundamental dynamics of social interactions, which could lay the foundation for clinical research and interventions in ASD. In order to provide first insights, the main goal of this thesis was to identify the non-pathological brain mechanisms in perceptual action prediction and action control within a social context. For this purpose, two functional magnetic resonance imaging (fMRI) experiments in healthy control participants were conducted: The first study of this thesis addressed the effect of observing communicative, i.e. predictive, actions on visual perception [interpersonal predictive coding (IPPC)]. By the use of point-light displays, we replicated behavioral findings of improved visual discriminability of a point-light agent after seeing a communicative as compared to an individual action of another point-light agent. Furthermore, our findings suggest a perceptual integration of social event knowledge implemented by the superior frontal gyrus (SFG) during predictive trials and a specific role of the amygdala in setting network configurations to meet the demands of the specific social context. Moving from a spectator perspective to direct involvement in a social interaction, the second study of this thesis examined the interaction of gaze processing and action control during an encounter with an anthropomorphic virtual character. The key finding of this second study comprises an increased functional coupling during high action control demands between the right temporoparietal junction (TPJ) as central gaze processing region and brain areas implicated in both action control processes and social cognition such as the inferior frontal gyri. The results of the two studies demonstrate that predictive social actions as well as direct gaze signals can modify multimodal functional integration in the brain, thereby recruiting and modulating activation in brain structures implicated in ASD. In this way, the two studies of this thesis underline the interdependence of social cognition and kinematic processes while providing a reference point for future studies on ASD