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Local vibration (LV) mainly stimulates primary afferents (Ia) and can induce a tonic vibration reflex (TVR) and an illusion of movement. This study aimed to evaluate the effect of these two phenomena on maximal voluntary isometric contraction (MVIC) capacity. LV (80 Hz) was applied to the wrist flexor muscles in two randomized experiments for 6 min. LV conditions were adjusted to promote either TVR (visual focus on the vibrated wrist) or ILLUSION [hand hidden, visual focus on electromyographic activity of the flexor carpi radialis muscle (FCR)]. Mechanical and electromyographic (EMG) responses of the FCR and extensor carpi radialis muscles were recorded during MVIC in flexion and extension and during electrically evoked contractions at supramaximal intensity. Measurements were performed before (10 min and just before) and after (0 and 30 min) LV protocol. An increase in FCR EMG was observed during LV in the TVR condition (+340%) compared with the illusion condition (P = 0.003). In contrast, the movement illusion was greater in the ILLUSION condition (assessed through subjective scales) (P = 0.004). MVIC was reduced in flexion only after the TVR condition (≈ − 7 % , all P < 0.034). Moreover, the decrease in force was correlated with the amount of TVR recorded on the FCR muscle (r = −0.64, P = 0.005). Although potentiated doublets of each muscle did not evolve differently between conditions, a decrease was observed between the first and the last measure. In conclusion, when conducting research to assess maximal strength, it is necessary to have better control and reporting of the phenomena induced during LV. NEW & NOTEWORTHY: The maximal force production of the vibrated muscle is reduced after 6 min of LV only in TVR condition. Furthermore, the amount of TVR is negatively correlated with this force decrease. When measuring the effects of LV on maximal force production, it is important to control and report any phenomena induced during vibration, such as TVR or movement illusion, which can be achieved by recording EMG activity of vibrated muscle and quantifying illusion. [ABSTRACT FROM AUTHOR]

We present a novel, movement-based haptic illusion called the “snake effect.” Unlike apparent motion or sensory saltation, the snake effect feels wavy and creepy as though the belly of a slithering snake is making and breaking contact with the skin. This illusion is achieved by modulating the amplitudes of vibrotactile pulses sent successively to an array of tactors. Pilot testing established the following signal parameters for creating the snake effect: a minimal pulse duration of 1.69 s, carrier frequency in the range of 200-300 Hz, amplitude modulation of the carrier with a sine, sine-squared or Gaussian waveform (shown to be more effective than a linear up-and-down ramp), and a peak amplitude of 30 dB above detection threshold. The main experiment examined the most effective signal onset asynchrony (SOA) ranges by estimating the upper and lower SOA thresholds using a one-up one-down adaptive procedure with interleaved ascending and descending series. The results indicate an optimal SOA range from 271.5 ms to 798 ms with a midpoint of 535 ms. The snake effect is a vivid illusion that can be used as a distinctive signal for encoding information and to enhance immersion and engagement in gaming and entertainment. [ABSTRACT FROM AUTHOR]

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.

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. 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 <0.05). Notably, a significant increase in M1 excitability occurred only when the directions of the observed and illusory movements were congruent. Further, a significant positive linear relationship was found between the amount of M1 excitability increase and the vividness of the perceived illusion (P = 0.03). Finally, the tactile stimulation coupled with AO was not sufficient to induce changes in M1 excitability as well as the KI alone. All these findings indicate the importance of combining different sensory input signals to induce plasticity in M1, and that proprioception is the most suitable sensory modality to allow it. 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 FROM AUTHOR]

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.

Vibration applied to muscle tendons induces an illusory perception of movement by activating spindle receptors and Ia afferent fibers. While neural structures supporting such illusions are quite defined, functional and psychophysical correlates of their perception have not been deeply investigated. The authors aimed at exploring subjective perception of illusory movements thanks to a repeated-stimulation multimodal approach. The integrated analysis of electroencephalography, source data (standardized low-resolution brain electromagnetic tomography-sLORETA), and psychophysical evaluation pointed at the activation of a frontoparietal sensorimotor network, with prefrontal-medial regions mainly involved in supporting the awareness for illusory movements. Further, illusions showed consistency in terms of presence, vividness, and duration. Finally, superior parietal structures seemed to play an important role in self-attribution of agency and ownership during such experiences. [ABSTRACT FROM AUTHOR]

Muscle vibrations can induce motor responses and illusions of complex movements. However, inducing gait-like cyclical movements and illusions requires the application of multiple fast alternating vibrations to lower-limb muscles. The objectives were (1) to test the feasibility of delivering complex vibrations in a time-organized manner and (2) to illustrate the possibility of inducing alternate gait-in-place-like movements using these vibrations. Patterns of vibration, produced by 12 vibrators applied bilaterally on the flexor and extensor muscle groups of the lower limbs, were based on normal gait kinematics. We tested 1 s and 2 s cycle patterns of vibration. Vibrator responses were assessed using auto- and crosscorrelations and frequency analyses based on accelerometry measurements, and compared between patterns. High auto- (>0.8) and crosscorrelation (>0.6) coefficients demonstrated a good response by the vibrators to the control signal. Vibrations induced cyclical, low-amplitude stepping-in-place movements that mimicked alternate walking movements with both legs, with 1 s and 2 s cycle durations, in one nondisabled participant and one participant with American Spinal Injury Association Impairment Scale B spinal cord injury standing, relaxed, with body-weight support. Electromechanical vibrators can deliver complex cyclical vibrations and trigger gait-like lower-limb movements. These results warrant the application of these vibration patterns on individuals with sensorimotor impairments to test their potential in gait rehabilitation. [ABSTRACT FROM AUTHOR]

Abstract: This study aims to identify the cerebral networks involved in the integrative processing of somesthetic inputs for kinesthetic purposes. In particular, we investigated how muscle proprioceptive and tactile messages can result in a unified percept of one''s own body movements. We stimulated either separately or conjointly these two sensory channels in order to evoke kinesthetic illusions of a clockwise rotation of 10 subjects’ right hand in an fMRI environment. Results first show that, whether induced by a tactile or a proprioceptive stimulation, the kinesthetic illusion was accompanied by the activation of a very similar cerebral network including cortical and subcortical sensorimotor areas, which are also classically found in passive or imagined movement tasks. In addition, the strongest kinesthetic illusions occurred under the congruent proprio-tactile co-stimulation condition. They were specifically associated to brain area activations distinct from those evidenced under the unimodal stimulations: the inferior parietal lobule, the superior temporal sulcus, the insula-claustrum region, and the cerebellum. These findings support the hypothesis that heteromodal areas may subserve multisensory integrative mechanisms at cortical and subcortical levels. They also suggest the integrative processing might consist of detection of the spatial coherence between the two kinesthetic messages involving the inferior parietal lobule activity and of a detection of their temporal coincidence via a subcortical relay, the insula structure, usually linked to the relative synchrony of different stimuli. Finally, the involvement of the superior temporal sulcus in the feeling of biological movement and that of the cerebellum in the movement timing control are also discussed. [Copyright &y& Elsevier]

Abstract: The present study aimed to investigate cortical activity associated with perception of illusory hand movements elicited by tendon vibration using magnetoencephalography (MEG) in humans. We compared MEG responses in two conditions of stimulation, “illusion” and “no illusion”. In the “illusion” condition, covibration at different frequencies applied on the tendons of the right wrist flexor and extensor muscle groups evoked illusory movements of the hand. In the “no illusion” condition, covibration was delivered at the same frequency on both tendon groups and no movement was perceived. In both experimental conditions, equivalent current dipoles (ECD) were identified in each of four time windows: 0–200 ms, 200–400 ms, 400–600 ms and 600–800 ms. Our data showed similar activation in S1, superior parietal gyrus and supramarginal gyrus in both conditions, whereas the supplementary motor area, M1 and the left angular gyrus were found active in the “illusion” condition only. Our results confirmed the role of posterior parietal areas as well as motor areas in the arising of kinesthetic sensations. The hypothesis of an interaction between the angular gyrus and the primary motor area occurring about 400 ms after the beginning of the stimulation is discussed. [Copyright &y& Elsevier]