Ego-centric spatial representations and their reference frames in the human brain

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Maintaining spatial representations in distinct reference frames is essential for human behaviour. While visual input is received in retinotopic coordinates, vestibular and auditory input are head-centred, and limb-actions are inherently body-centred. They need to be invariant to eye- or head-movements, and may occur outside the visual field of view. Even our conscious experience of the environment is non-retinotopic: we experience the visual world around us as stable even when eye- or head-movements shift the visual scene across the retina several times per second. Egocentric maps of our full surroundings are thus essential for the integration between different senses such as audition, vision, and touch, especially when head- or body-movements shift different parts of the environment in- and out of the field of view. The stable phenomenal experience of our surrounding as well as all interactions with it are thus based on the continual updating and maintenance of internal spatial maps in the face of changing sensory input during self-motion. Such representations have been referred to as parietal window, egocentric representation or spatial image. In healthy humans, almost nothing is known about neural representations of egocentric maps of our full surroundings that include, but also go beyond, our visual field of view. In this proposal we aim to shed light on such egocentric maps in the human brain. In particular we aim to distinguish between head- and body-centred spatial representations across the human brain, and to examine the extent to which their reference frames are affected by head- or body-centred attention. This will be achieved by extensive training of participants, the use of virtual reality, and an unconventional fMRI paradigm that involves distinct head-to-body orientations. We will focus especially on regions of the perisylvian network whose lesion is associated to spatial neglect and that play a role in multisensory integration with vestibular senses, but also on parietal and temporal regions involved in spatial encoding. We plan a set of four sets of experiments, carried out by one researcher, using fMRI and transcranial magnetic stimulation (TMS) to probe functional and causal involvement of these regions. Importantly, the experiments are designed such that their results will be worthwhile regardless of their exact outcome.The results will provide unprecedented insights into neural mechanisms of egocentric spatial representations in the human brain and for the first time disentangle head- from body-centred neural spatial representations using a novel fMRI imaging approach. Our experimental questions are not only significant for basic cognitive neuroscience but may in the long run also help to better understand neural underpinnings of impaired brain representations of space, in particular in relation to spatial neglect and other disorders related to the interaction with the world.