A new method to elicit and measure movement illusions in stroke by means of muscle tendon vibration: the Standardized Kinesthetic Illusion Procedure (SKIP)

Corticospinal and Clinical Effects of Muscle Tendon Vibration in Neurologically Impaired Individuals. A Scoping Review

This review verified the extent, variety, quality and main findings of studies that have tested the neurophysiological and clinical effects of muscle tendon vibration (VIB) in individuals with sensorimotor impairments. The search was conducted on PubMed, CINAHL, and SportDiscuss up to April 2024. Studies were selected if they included humans with neurological impairments, applied VIB and used at least one measure of corticospinal excitability using transcranial magnetic stimulation (TMS). Two investigators assessed the studies' quality using critical appraisal checklists and extracted relevant data. The 10 articles included were diverse in populations and methods, generally rated as 'average' to 'good' quality. All studies reported an increased corticospinal excitability in the vibrated muscle, but the effects of VIB on non-vibrated muscles remain unclear. Positive clinical changes in response to VIB were reported in a few studies, such as a decreased spasticity and improved sensorimotor function. These changes were sometimes correlated with corticospinal effects, suggesting a link between VIB-induced plasticity and clinical improvements. Despite the limited and heterogeneous literature, this review supports the facilitatory influence of VIB on motor outputs controlling vibrated muscles, even with altered sensorimotor functions. It highlights knowledge gaps and suggests future research directions on VIB mechanisms and clinical implications.

Challenges and opportunities in testing sensorimotor processing with tendon vibration and transcranial magnetic stimulation in subacromial impingement syndrome: A case series

BACKGROUND

Non-invasive neurostimulation like muscle tendon vibration (VIB) and transcranial magnetic stimulation (TMS) can provide valuable insights on mechanisms underlying sensorimotor dysfunctions. However, their feasibility in the context of painful musculoskeletal disorders like shoulder impingement syndrome (SIS) remain uncertain.

METHODS

The present work used a case series design including 15 participants with SIS, as well as a secondary group-based analysis comparing participants with SIS to 15 healthy counterparts. Proprioceptive processing was tested by VIB-induced kinesthetic illusions of shoulder abduction, and TMS tested corticospinal excitability of the upper trapezius. Detailed individual data were collected, including any technical challenges and feasibility issues encountered.

RESULTS

VIB was in general well-tolerated and elicited a perceptible kinesthetic illusion in 13 participants with SIS and 14 controls. TMS presented with several challenges related to discomfort, fear-related behaviors, technical problems and high motor thresholds, especially in participants with SIS. It was only possible to collect all TMS measures in 5 participants with SIS (for both the painful and non/less-painful sides), in 7 controls on their dominant side and 10 controls on the non-dominant side. The only significant group-based analysis was a lower illusion speed/amplitude on the painful versus non-painful side in persons with SIS (p = 0.035).

CONCLUSION

Our study provides preliminary data on challenges encountered with TMS and VIB of trunk/proximal muscle in persons with SIS and healthy counterparts. It might help future studies to better address those challenges beforehand and improve the overall feasibility and impact of neurostimulation tools in musculoskeletal disorders.

Vibration-induced postural reactions: a scoping review on parameters and populations studied

Objective

Mechanical vibration is an effective way for externally activating Ia primary endings of the muscle spindles and skin mechanoreceptors. Despite its popularity in proprioception and postural control studies, there is still no review covering the wide variety of vibration parameters or locations used in studies. The main purpose of this scoping review was thus to give an overview of general vibration parameters and to identify, if available, the rationale for justifying methodological choices concerning vibration parameters.

Methods

Three databases (Pubmed, CINHAL, and SPORTDiscus) were searched from inception to July 2022. Included articles were to focus on the study of muscle spindles and skin mechanoreceptors vibration in humans and assess postural control. Following inclusion, data regarding demographic information, populations, vibration parameters and rationale were extracted and summarized.

Results

One hundred forty-seven articles were included, mostly targeting lower extremities (n = 137) and adults (n = 126). The parameters used varied widely but were most often around 80 Hz, at an amplitude of 1 mm for 10-20 s. Regarding rationales, nearly 50% of the studies did not include any, whereas those including one mainly cited the same two studies, without elaborating specifically on the parameter's choice.

Conclusion

This scoping review provided a comprehensive description of the population recruited and parameters used for vibration protocols in current studies with humans. Despite many studies, there remain important gaps of knowledge that needs to be filled, especially for vibration amplitude and duration parameters in various populations.

Variation of corticospinal excitability during kinesthetic illusion induced by musculotendinous vibration

Despite being studied for more than 50 years, the neurophysiological mechanisms underlying vibration (VIB)-induced kinesthetic illusions are still unclear. The aim of this study was to investigate how corticospinal excitability tested by transcranial magnetic stimulation (TMS) is modulated during VIB-induced illusions. Twenty healthy adults received vibration over wrist flexor muscles (80 Hz, 1 mm, 10 s). TMS was applied over the primary motor cortex representation of wrist extensors at 120% of resting motor threshold in four random conditions (10 trials/condition): baseline (without VIB), 1 s, 5 s, and 10 s after VIB onset. Means of motor-evoked potential (MEP) amplitudes and latencies were calculated. Statistical analysis found a significant effect of conditions (stimulation timings) on MEP amplitudes (P = 0.035). Paired-comparisons demonstrated lower corticospinal excitability during VIB at 1 s compared with 5 s (P = 0.025) and 10 s (P = 0.003), although none of them differed from baseline values. Results suggest a time-specific modulation of corticospinal excitability in muscles antagonistic to those vibrated, i.e., muscles involved in the perceived movement. An early decrease of excitability was observed at 1 s followed by a stabilization of values near baseline at subsequent time points. At 1 s, the illusion is not yet perceived or not strong enough to upregulate corticospinal networks coherent with the proprioceptive input. Spinal mechanisms, such as reciprocal inhibition, could also contribute to lower the corticospinal drive of nonvibrated muscles in short period before the illusion emerges. Our results suggest that neuromodulatory effects of VIB are likely time-dependent, and that future work is needed to further investigate underlying mechanisms.NEW & NOTEWORTHY The modulation of corticospinal excitability when perceiving a vibration (VIB)-induced kinesthetic illusion evolves dynamically over time. This modulation might be linked to the delayed occurrence and progressive increase in strength of the illusory perception in the first seconds after VIB start. Different spinal/cortical mechanisms could be at play during VIB, depending on the tested muscle, presence/absence of an illusion, and the specific timing at which corticospinal drive is tested pre/post VIB.

An investigation of proprioception illusion using a stimulator with feedback control

It is possible to create illusions of limb movements using vibrations over the skin. If a muscle is vibrated it can feel as if the limb is moving while it remains still. These illusions have been studied for decades but it is not yet entirely clear how to create them effectively and repeatedly. In this study, three parameters were varied; the frequency of the vibration, the stimulation site and the arm position. A closed loop control of the vibration frequency was used to ensure a fixed frequency over the stimulation time and across the participants. The experiment included twenty-five able-bodied participants (mean age 32±7 years, 9 females). A hanging arm position was introduced with the aim to increase the success rate of illusions compared to other studies. Twenty-four participants felt an illusion across all scenarios. The results highlight that tactile feedback affects the illusion.

Repetitive Peripheral Magnetic Stimulation to Improve Ankle Function and Gait in Cerebral Palsy at Adulthood: An open-label Case Study

Repetitive peripheral magnetic stimulation (rPMS) is noninvasive and painless. It drives plasticity of the primary motor cortex (M1) in children with cerebral palsy (CP) and this improves the ankle function and gait. Our study explored whether rPMS of muscles could influence motricity in an adult CP case. A 30-year-old woman with mixed CP participated in four sessions (S1 to S4, one per week) where rPMS was applied bilaterally on leg and trunk muscles (tibialis anterior-TA, hamstrings, transverse abdominis, paraspinal multifidus). Clinical scores and M1 excitability (probed by transcranial magnetic stimulation) were tested at pre-rPMS at S1 (baseline) and S4, then 40 days later (follow-up). The active ankle dorsiflexion was significantly increased and the plantar flexors resistance to stretch reduced as compared to baseline. The improvement of the ankle function was carried-over to the quality of locomotor patterns. Changes persisted until follow-up and were paralleled by drastic changes of M1 excitability. These original findings of rPMS influence on M1 plasticity and motricity are promising for the functional improvement of adult people living with CP and should be replicated in larger-sampled studies.

The analgesic effect of localized vibration: a systematic review. Part 1: the neurophysiological basis

INTRODUCTION

The analgesic action of localized vibration (LV), which is used in rehabilitation medicine to treat various clinical conditions, is usually attributed to spinal gate control, but is actually more complex. The aim of this review is: 1) to provide neurophysiological insights into the mechanisms underlying the ways in which afferent activity set up by LV induces analgesia through interactions with the nociceptive system throughout the nervous system; 2) to give a broader vision of the different effects induced by LV, some of them still related to basic science speculation.

EVIDENCE ACQUISITION

The Medline, EMBASE, AMED, Cochrane Library, CINAHL, Web of Science and ROAD databases were searched for animal and human neurophysiological and neurohormonal studies related to the direct effects of LV on nociceptive transmission and pain perception and were supplemented by published books and theses.

EVIDENCE SYNTHESIS

The spinal gate control mechanism through Aβ-fibers activation seems to be the most effective antinociceptive system activated by LV at frequencies between 100 and 250 Hz (high-frequency LV [HF-LV]) when applied in the same segment as the pain. A gating effect can be obtained also when it is applied contralaterally to the painful site or to adjacent dermatomes. Kinesthetic illusions of movement induced by HF-LV may induce a stronger analgesic effect. Activation of C-mechanoreceptors induced by a massage-like LV of low frequency and low intensity may interfere with pain through the activation of the limbic system. This action does not involve any gating mechanism. Frequency is more important than intensity as different frequencies induce activity in different cortical and cerebellar areas; these activations may be related to plastic cortical changes tentatively reversing pain-related maladaptive disorganization. Distraction/shift of attention or cortisol-mediated stress-induced analgesia are not involved in LV analgesic action in humans for both LF and HF. The release of opioidergic neuropeptides (analgesia not reversed by naloxone) as well as a reduction in substance P in the CSF does not seem to play a major role in the HF-LV action. Decrease in calcitonin and TRPV1 expression in the trigeminal ganglia in animals has been induced by HF-LV but the role of LF-LV is not completely deciphered. Both high and low LV induce the release of oxytocin, which may induce antinociceptive responses in animals and contribute to controlling pain in humans.

CONCLUSIONS

Although many aspects of LV-induced pain alleviation deserve more in-depth basic and translational studies, there are sound neurophysiological reasons for using LV in the therapeutic armamentarium of pain control. Laboratory animal and human data indicate that LV relieves pain not only by acting on the spinal gate, but also at higher levels of the nervous system.

Visual feedback improves movement illusions induced by tendon vibration after chronic stroke

BACKGROUND

Illusion of movement induced by tendon vibration is commonly used in rehabilitation and seems valuable for motor rehabilitation after stroke, by playing a role in cerebral plasticity. The aim was to study if congruent visual cues using Virtual Reality (VR) could enhance the illusion of movement induced by tendon vibration of the wrist among participants with stroke.

METHODS

We included 20 chronic stroke participants. They experienced tendon vibration of their wrist (100 Hz, 30 times) inducing illusion of movement. Three VR visual conditions were added to the vibration: a congruent moving virtual hand (Moving condition); a static virtual hand (Static condition); or no virtual hand at all (Hidden condition). The participants evaluated for each visual condition the intensity of the illusory movement using a Likert scale, the sensation of wrist's movement using a degree scale and they answered a questionnaire about their preferred condition.

RESULTS

The Moving condition was significantly superior to the Hidden condition and to the Static condition in terms of illusion of movement (p < 0.001) and the wrist's extension (p < 0.001). There was no significant difference between the Hidden and the Static condition for these 2 criteria. The Moving condition was considered the best one to increase the illusion of movement (in 70% of the participants). Two participants did not feel any illusion of movement.

CONCLUSIONS

This study showed the interest of using congruent cues in VR in order to enhance the consistency of the illusion of movement induced by tendon vibration among participants after stroke, regardless of their clinical severity. By stimulating the brain motor areas, this visuo-proprioceptive feedback could be an interesting tool in motor rehabilitation. Record number in Clinical Trials: NCT04130711, registered on October 17th 2019 ( https://clinicaltrials.gov/ct2/show/NCT04130711?id=NCT04130711&draw=2&rank=1 ).

Proprioceptive Augmentation With Illusory Kinaesthetic Sensation in Stroke Patients Improves Movement Quality in an Active Upper Limb Reach-and-Point Task

Stroke patients often have difficulty completing motor tasks even after substantive rehabilitation. Poor recovery of motor function can often be linked to stroke-induced damage to motor pathways. However, stroke damage in pathways that impact effective integration of sensory feedback with motor control may represent an unappreciated obstacle to smooth motor coordination. In this study we investigated the effects of augmenting movement proprioception during a reaching task in six stroke patients as a proof of concept. We used a wearable neurorobotic proprioceptive feedback system to induce illusory kinaesthetic sensation by vibrating participants' upper arm muscles over active limb movements. Participants were instructed to extend their elbow to reach-and-point to targets of differing sizes at various distances, while illusion-inducing vibration (90 Hz), sham vibration (25 Hz), or no vibration was applied to the distal tendons of either their biceps brachii or their triceps brachii. To assess the impact of augmented kinaesthetic feedback on motor function we compared the results of vibrating the biceps or triceps during arm extension in the affected arm of stroke patients and able-bodied participants. We quantified performance across conditions and participants by tracking limb/hand kinematics with motion capture, and through Fitts' law analysis of reaching target acquisition. Kinematic analyses revealed that injecting 90 Hz illusory kinaesthetic sensation into the actively contracting (agonist) triceps muscle during reaching increased movement smoothness, movement directness, and elbow extension. Conversely, injecting 90 Hz illusory kinaesthetic sensation into the antagonistic biceps during reaching negatively impacted those same parameters. The Fitts' law analyses reflected similar effects with a trend toward increased throughput with triceps vibration during reaching. Across all analyses, able-bodied participants were largely unresponsive to illusory vibrational augmentation. These findings provide evidence that vibration-induced movement illusions delivered to the primary agonist muscle involved in active movement may be integrated into rehabilitative approaches to help promote functional motor recovery in stroke patients.