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KEY POINTS The combination of action observation (AO) and a peripheral nerve stimulation has been shown to induce plasticity in the primary motor cortex (M1). However, using peripheral nerve stimulation little is known about the specificity of the sensory inputs. The current study, using muscle tendon vibration to stimulate muscle spindles and transcranial magnetic stimulation to assess M1 excitability, investigated whether a proprioceptive stimulation leading to a kinaesthetic illusion of movement (KI) was able to evoke M1 plasticity when combined with AO. M1 excitability increased immediately and up to 60 min after AO-KI stimulation as a function of the vividness of the perceived illusion, and only when the movement directions of AO and KI were congruent. Tactile stimulation coupled with AO and KI alone were not sufficient to induce M1 plasticity. This methodology might be proposed to subjects during a period of immobilization to promote M1 activity without requiring any voluntary movement. ABSTRACT Physical practice is crucial to evoke cortical plasticity, but motor cognition techniques, such as action observation (AO), have shown their potentiality in promoting it when associated with peripheral afferent inputs, without the need of performing a movement. Here we investigated whether the combination of AO and a proprioceptive stimulation, able to evoke a kinaesthetic illusion of movement (KI), induced plasticity in the primary motor cortex (M1). In the main experiment, the role of congruency between the observed action and the illusory movement was explored together with the importance of the specificity of the sensory input modality (proprioceptive vs. tactile stimulation) to induce plasticity in M1. Further, a control experiment was carried out to assess the role of the mere kinaesthetic illusion on M1 excitability. Results showed that the combination of AO and KI evoked plasticity in M1, with an increase of the excitability immediately and up to 60 min after the conditioning protocol (P always

The technique of vibration-induced illusory movement has been used to study the mechanisms of perception and the brain network responsible for eliciting kinesthesia since it was first reported by Goodwin and colleagues in 1972. Vibration applied to the skin surface over the tendon of limb muscles excites primary afferent spindles, and subjects experience movement sensations as if the vibrated muscle were stretched, despite the limb being immobile. In addition, tendon vibration can induce tonic muscle activities in both the vibrated muscle and its antagonistic muscles. It was formerly believed that these motor responses accompanied the kinesthetic illusion of the vibrated limb. However, if subjects relax their limb completely and focus their attention on the movement sensed during vibration, a movement illusion can be elicited without any motor responses. This review focuses on the relationship between the elicitation of vibration-induced kinesthetic illusions and experimental conditions, and may provide insight into differences among studies of kinesthetic illusion.

BackgroundStrategic vibration of musculotendinous regions of a limb elicits illusionary sensations of movement. As a rehabilitation technique, this 'kinesthetic illusion' has demonstrated beneficial results for numerous sensory-motor disorders. However, literature shows little consistency in the vibration parameters or body positioning used, and their effects have yet to be comprehensively investigated.ObjectiveTo characterize the effects of the vibration amplitude, frequency, and limb position on the kinesthetic illusion.MethodsMovement illusions were induced in 12 participants' biceps and triceps. The effect of amplitude (0.1 to 0.5 mm), frequency (70 to 110 Hz), and two limb positions were quantified on the strength of illusion (SOI), range of motion (ROM) and velocity.ResultsAmplitude significantly affected the illusionary SOI, ROM and velocity in the biceps and triceps (p< 0.05). Increasing amplitude resulted in an increase of all three output variables. Limb position showed an effect on illusionary velocity in the biceps as well as ROM and velocity in the triceps (p< 0.05). Frequency demonstrated no statistical effect.ConclusionsAmplitude demonstrated the most profound impact on the kinesthetic illusion in the experimental ranges tested. This work may help guide clinicians and researchers in selecting appropriate vibratory parameters and body positions to consistently elicit and manipulate the kinesthetic illusion.