Multiscale body maps in the human brain

A large number of brain regions are dedicated to processing information from the body in order to enable interactions with the environment. During my thesis, I studied the functional organization of brain networks involved in processing bodily information. From the processing of unimodal low-level features to the unique experience of being a unified entity residing in a physical body, the brain processes and integrates bodily information at many different stages. Using ultra high-field functional Magnetic Resonance Imaging (fMRI), I conducted four studies to map and characterize multiscale body representations in the human brain. The goals of my thesis were first to extend the actual knowledge about primary sensorimotor representations, and second to develop novel approaches to investigate more complex and integrated forms of body representations. In studies I and II, I first investigated how natural touch was represented in the three first cortical areas processing tactile information. I applied a mapping procedure to identify in each of these three areas the somatosensory representations of 24 different body parts on hands, feet and legs at the level of single subjects. Using fMRI and resting-state data, I combined classical statistical analyses with modern methods of network analysis to describe the functional properties of the formed network. In study III, I applied these methods to investigate primary somatosensory and motor representations in a rare population of patients. Following limb loss, the targeted muscle and sensory reinnervation (TMSR) procedure enables the intuitive control of a myoelectric prosthesis and creates an artificial map of referred touch on the reinnervated skin. I mapped the primary somatosensory and motor representations of phantom sensations and phantom movements in TMSR patients. I investigated whether sensorimotor training enabled via TMSR was associated with preserved somatosensory and motor representations compared to healthy controls and amputee patients without TMSR. Finally in study IV, I studied brain regions involved in the subjective body experience. Following specific manipulations of sensorimotor information, it is possible to let participants experience a fake or virtual hand as their own and to give them the sensation of being in control of this hand. Using MR-compatible robotics and virtual reality, I investigated the brain regions associated with the alteration of the sense of hand ownership and the sense of hand agency. The present work provides important findings and promising tools regarding the understanding of brain networks processing bodily information. In particular, understanding the functional interactions between primary unimodal cortices and networks contributing to subjective body experience is a necessity to promote modern approaches in the fields of neuroprosthetic and human-machine interactions.