Developing a new sensorimotor body representation for an additional robotic limb.

Adding an artificial body part could expand our motor abilities. But can our brain develop an integrated multisensory representation of an extra limb in addition to our own body? In BodyPlus, we will explore whether the brain can extend our body representation to incorporate an additional robotic thumb, known as the Third Thumb. We will compare participants’ behaviour and brain responses before and after a 4-day training period where they learn to control the Third Thumb. In Work Package 1 (WP1), we will use two behavioural paradigms to determine whether participants develop novel sensorimotor links through training. Specifically, we will examine whether participants learn to integrate touch location with posture, and sensory information with movement predictions. We will use computational modelling to identify behavioural biases indicative of optimal Bayesian integration. In WP2, we will scan participants using fMRI as they control the Third Thumb. We will compare conditions where the Thumb’s movement matches or doesn’t match the movements participants learned during training, allowing us to identify brain regions that integrate Third Thumb movement with sensory predictions. Furthermore, we will use brain decoding to determine if the newly acquired representation of the Third Thumb compares with the representation of participants' own right thumb, or of a familiar tool. In WP3, we will examine how participants behaviour changes when we remove key sensory inputs, which were available during motor training, or modify the expected movement of the Third Thumb. This will allow us to determine the resilience and generalisability of the newly formed Third Thumb representation. Overall, BodyPlus will identify the key components that the brain uses to develop a new body representation. This knowledge will guide us to design additional body parts that can seamlessly integrate with our movements and provide new ways to interact with the world.