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Category: Project

Description: The incorporation of an external body object with visual feedback, such as in the rubber hand illusion (RHI) (classic RHI – vision involved), is known to affect the planning of the movement of the limb where the object is incorporated (movement planning). This is usually considered to happen due to a change in body ownership. However, it is also known that change in body ownership might occur without visual feedback. It is yet not known whether change in motion planning still happens if the change in body ownership occurs without visual feedback. In other words, we are interested in whether a change in body ownership, in the absence of a visual feedback, still results in a change in motion planning. This investigation is important because it would first clarify the role and significance of the visual feedback provided by the sight of the rubber hand in previous studies and would perhaps explain the differences in findings of different studies. In this study we use the RHI paradigm to test whether a change in motion planning can still be observed in the absence of visual feedback. Hence, we incorporate the rubber hand through proprioceptive and tactile feedback only (somatic RHI) without any visual feedback. We hypothesize that when the incorporation of the rubber hand occurs because of proprioceptive and tactile information only, this is sufficient to generate changes in motion planning. Our study explores this by measuring hand movements (changes in maximum Grip Aperture, maximum GA) and associated brain activations within the dorsal stream (near-infrared spectroscopy). Thirty-two healthy individuals performed grasping actions towards a target before and after a somatic RHI. The exposure to the somatic RHI results in a change in body ownership which can be observed in the form of a sensory uncertainty in the movements of the participant’s hand. We will capture a sensory uncertainty in the movement with registering a reduced maximum GA. If the somatic RHI affects grasping planning, we also expect a corresponding change in the brain activation within the dorsal stream where movement planning occurs. Monitoring the brain changes within the dorsal stream will inform us of the change in pattern of brain activation if a change in motion planning occurs. Our findings show that the incorporation of an external body object through touch has no effect on maximum GA. The embodiment of a rubber hand based on tactile and proprioceptive information only partially affected brain activation. We observed a partial deactivation (trend) in the right supplementary motor area following the somatic RHI. Overall, our behavioural and neuroimaging data do not support an effect on maximum GA when the incorporation of a rubber hand is based on proprioceptive and tactile information only. This implies the critical role of the visual input provided by the sight of the rubber hand in the results of previous studies. Please find attached the database in the "Files" section