Vibration-induced Movement Illusion Causes Cerebral Haemodynamic Changes: A fNIRS Study.

Perceived sensations of limb and movements (kinesthesia) allow us to situate ourselves without visual feedback and not dedicate all of our attention to everyday tasks such as walking or taking and holding an object. These perceived conscious sensations come from receptors called proprioceptors which are located in the skin, joints and muscles. When a limb is moving and a muscle is stretched, the main sensation of limb stretching comes from the stimulation of a proprioceptor called the muscle spindle, more specifically from its primary ending called the 1a fibber. Artificially, 1a fibbers can be (optimally) stimulated by vibration of the muscle around 80 Hz. When stimulating 1a fibbers of the triceps, a signal of stretching is produced and an illusion of flexion can be felt as long as their no other contrary feedback involved such as vibration of the antagonist muscle or visual feedback of the immobile limb as it provides a more reliable information to the brain. As of now, neural correlates to muscle spindle vibration and illusion of movement have not been fully characterize in healthy participants and are not known in stroke participants.

To investigate the effect of vibration-induced illusion of movement on cerebral activations in healthy and stroke participants, the investigators propose to use an innovative tool of neuroimaging, the functional near infrared spectroscopy (fNIRS).

fNIRS allows to investigate cortical cerebral activations by measuring cerebral haemodynamic variations. Indeed, just like fMRI, it relies on the haemodynamic response function (HRF) caused by neurovascular coupling. Its portability and non-invasiveness make it a great tool to study brain activations in a more ecological environment (in a standing or sitting position for example).

This research aims to study and compare the subjective sensation of movement and the cortical cerebral areas involved in muscle spindle vibration and illusion of movement in healthy and stroke participants.

The protocol consists of 4 or 2 different conditions (repeated 2 times) of vibration-induced illusion of movement in healthy and stroke participants respectively, resulting in 8 or 4 vibration blocks with 3 vibrations per block: