Social dimension of primates’ peripersonal space – MySPACE

Our first objective was to understand how the emotions conveyed by faces in the space close to the body affect our perception abilities, our physiological state and our brain activity. We therefore combined behavioral analysis, physiology and neuroimaging (functional Magnetic Resonance Imaging - fMRI) to characterize the impact of a social element, by varying its emotional content (a neutral, happy or angry face). ), its position in the space that surrounds us (near or far) on the representation of peripersonal space. Then, the notion of peripersonal space having initially been defined on the basis of the properties of neurons recorded in monkeys, our second objective was to bridge the gap between this data and the brain activities identified in neuroimaging in humans, a link that is far from being elucidated to date. This project presented two important methodological challenges: 1) the development of protocols exploiting virtual reality to precisely control visual information at different distances from our body and 2) the development of similar protocols applicable to humans and monkeys. These developments have made it possible to remove a technological barrier by measuring brain activity in the presence of avatars that come close physically - and virtually - to the participants whose way of perceiving this information and their bodily responses were measured. Finally, in order to establish causal relationships between structure and function, we tested the representation of space close to the body in patients with selective lesions while recording their internal state.

With MySpace, we have conducted fMRI studies in humans and monkeys allowing us to reconcile the two sources of knowledge of the representation of EPP on the primate brain. This critical objective allows us to relate neuronal properties to activations recorded in fMRI, a link that is far from clear to date. We also compared our results in a real versus virtual situation, the latter being increasingly used for theoretical or therapeutic purposes in biomedical research. The results of these two studies show relatively similar activations involved in the processing of stimuli in the close space, whether with a real object 2 cm from the face or a virtual object 30 cm from the body. In humans, our results also demonstrate that the near space is, in itself, special and benefits from improved perceptual processing, even under extremely disadvantageous conditions, to allow us to interact quickly and flexibly with our surroundings and optimize behavioral responses both towards objects and other individuals around us to avoid potential threats. In particular, with social stimuli in near space such as faces, our results highlight the subtle interactions between the characteristics of these social factors (such as for example their gender and their emotional state), our specific characteristics (our sex and our personality traits) and our physiological reactions (reflecting our internal state measured via pupil diameter, heart rate and heart rate variability or facial muscle activity). These results have led us to propose a role for PPS in social interactions and the notion of interpersonal distance, beyond the sensorimotor functions that are usually attributed to it. This idea is in line with the conceptions of PPS in relation to self-awareness, by emphasizing the participation of interoceptive signals and our own characteristics in the perception of the environment of the stimuli presented close to the body. We explored this hypothesis in patients with lesions of the temporal lobe following surgical resection of a glioma. Thus, the results and developments of MySpace open the way to new and very interesting perspectives on the functions of PPS and its potential role in social interactions.

All of this work, at the interface between neuroscience and social psychology, has shed new light on how social information close to our body affects our daily behaviors by shaping our perception of the world and interactions with our peers. The immersive virtual reality approaches developed as part of the MySpace project have made it possible to remove a technological barrier by measuring brain activity with visual information that physically - and virtually - approaches participants. The benefit of lifting these obstacles represents a major asset of this project. The research question at the heart of the MySpace project concerns the social dimension of peripersonal space (the space around the body), a question that strongly resonates with the notion of social distancing which is discussed with COVID-19. These data allow us to better understand how the brain enables distance adjustments in social interactions. Understanding how social information modulates this space could pave the way for new strategies to mitigate it, and the use of virtual reality could represent a promising avenue. One of the avenues that arises from MySpace and that we are currently exploring is the possibility of training participants to reproduce facial emotions and to test the impact of this training on interpersonal distance, an avenue that could potentially prove to be interesting in helping some people. patient populations to renew social dialogue with their peers. Our preliminary results show that after training with facial expressions, interpersonal distances are significantly altered. Finally, the possibility of following the brain activity of participants in a virtual reality environment where avatars evolve is particularly relevant in the face of the recent emergence of metaverse technology, these virtual parallel universes under development.

At the end of the MySpace project at the end of September 2021, three articles were published as well as a book chapter. One article is under review and five more are in preparation. A doctoral thesis entitled «Social dimension of the Peri-personal space of primates« was defended at the University Claude Bernard Lyon 1 (Specialty Neurosciences) as part of the project. Two new collaborations have been developed, one with a research laboratory in Italy and one with a private company specializing in the production of animated films based in Lyon. As part of the project, we developed several protocols using virtual reality to study the issue of space around the body and these developments offer interesting perspectives currently being tested in patients.

In everyday life, humans and animals evolve in an environment composed of various kinds of objects with which they dynamically interact. Very often, the appropriate interaction with objects is crucially dependent on an effective optimization of the distance between the subject’s body and the objects in space. Even though we perceive the space surrounding us as a cartesian continuum, the region of space near the body where physical interactions with the environment take place is a special region, termed peripersonal space (PpS). Yet, our world is not only made of objects. Hence, the world of human and non-human animals is first and foremost a social world. In this social world, a comfort zone is necessary to regulate the interpersonal distance between selves and others and thus avoid discomfort or even anxiety. Much less is known about this social dimension of PpS than about the physical, object-related function of PpS. MySPACE will explore the behavioral determinants and the neural markers of this crucial, yet neglected, dimension of PpS. The findings could benefit patients whose PpS representation is altered by psychiatric disorders such as post-traumatic stress disorder, autism spectrum disorders, social phobias and the extreme social withdrawal known as hikikomori. The size of PpS comfort zone offers a measure of social dysfunctions in these pathologies. Understanding how the brain codes the social dimension of PpS may pave the way to new strategies to alleviate them.