Proprioception involves the sense of limb position and movement of body parts. It is critical for motor control, as without knowing where your body parts are it is impossible to move them accurately. Proprioception relies on the integration of various inputs, from muscle spindle receptors, Golgi tendon organs, skin stretch receptors, visual, auditory and vestibular inputs, and signals of motor command. How and where these signals are integrated in the human brain is still unclear.
Here we will use state-of-the-art brain imaging and brain stimulation methods in combination with perceptual illusions to identify neuronal populations that are involved in the integration of multisensory and efferent motor command signals for proprioception. Our hypothesis is that the primary motor cortex is involved in this process by storing a common neuronal representation of motor commands and movement sensations. Furthermore, the posterior parietal cortex is hypothesised to play an essential role in the integration of multisensory signals to optimise the sense of limb position.
To test these predictions we will use limb-movement illusions induced by different combinations of efferent or afferent signals. In the efferent-induced illusory condition, subjects perceive movement when they try to move a limb, while this movement is prevented by either an ischemic or a physical block. In the afferent-induced condition, subjects perceive movement when their muscle stretch receptors are stimulated with tendon vibration. The role of visual signals will be studied by providing visual feedback of moving limbs with virtual reality technology. To identify groups of neurons with specific properties, we will use fMRI-adaption methods that extend the spatial limitation of traditional fMRI. After having identified key areas associated with proprioception, we will examine the causal interactions between them using neuronavigation-guided single-pulse and repetitive transcranial magnetic stimulation.
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