BRAINPROP

Brain mechanisms of human limb movement sense

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 Obiettivo del progetto (Objective)

'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.'

Introduzione (Teaser)

Proprioception refers to our ability to sense the position and movement of our limbs through complex signal integration in the brain. EU-funded researchers investigated the inner workings of the brain during this process.

Descrizione progetto (Article)

Proper proprioception requires input to the brain from several sources such as receptors from skin and muscle as well as the visual, auditory and vestibular system. The brain then integrates these signals to generate accurate output signals for movement.

Scientists of the 'Brain mechanisms of human limb movement sense' (BRAINPROP) project investigated the role of the primary motor cortex in the brain in mediating proprioception. BRAINPROP used both functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulator (TMS) to elucidate how the brain processes proprioceptive information.

TMS experiments on hand muscles showed differences in their proprioceptive representation in the motor cortex, suggesting that such representation is task and position dependent.

A multi-voxel pattern analysis (MVPA) technique was used in fMRI experiments to collect information during motor cortex activation from passive hand movements. Unlike the normally used general linear model, MVPA successfully differentiated between activation patterns in the motor areas for the selected hand positions. This provided novel insight into motor cortex activity for hand position sensing during flexion and extension.

Another interesting approach involved application of a cuff around the upper arm of participants to induce temporary paralysis of the forearm during fMRI experiments. Participants then used the paralysed hand to push with varying force. Imaging data revealed that despite lack of signals from the skin and muscle, motor signals were enough to activate proprioceptive representations in the motor cortex.

Project outcomes have improved our understanding of how the brain processes proprioceptive signals to accurately sense position and generate movement. Such knowledge could prove invaluable in rehabilitation of patients after a stroke or in the use of prosthetics.