The Modulatory Effect of Visually Induced Kinesthetic Illusion on Spinal Reflexes: A Neuroscientific Study

Academic Background

In the fields of neuroscience and rehabilitation medicine, kinesthetic illusion is a phenomenon of virtual motion perception induced by visual stimulation. This phenomenon has been clinically proven to effectively suppress spasticity, particularly showing potential in the rehabilitation of stroke patients. However, despite preliminary validation of its clinical effects, the underlying neural mechanisms remain unclear. Specifically, whether kinesthetic illusion can influence spinal-level neural circuits through the activation of central neural networks is still an unresolved question.

This study aims to explore whether kinesthetic illusion induced by visual stimulation (KinVIS) can affect spinal reflex circuits through the activation of central neural networks, particularly by modulating reciprocal inhibition and presynaptic inhibition in the spinal cord to suppress spasticity. This research not only helps reveal the neural mechanisms of kinesthetic illusion but may also provide new theoretical foundations for the rehabilitation of stroke patients.

Source of the Paper

This paper was co-authored by Kohsuke Okada, Megumi Okawada, Masaki Yoneta, Wataru Kuwahara, Kei Unai, Michiyuki Kawakami, Tetsuya Tsuji, and Fuminari Kaneko. These authors are affiliated with multiple research institutions, including the Department of Rehabilitation Medicine at Keio University School of Medicine and the Department of Physical Therapy at Tokyo Metropolitan University Graduate School of Human Health Sciences. The paper was first published on November 12, 2024, in the Journal of Neurophysiology, with the DOI 10.1152/jn.00042.2024.

Research Process

1. Study Participants and Experimental Design

The study recruited 17 healthy participants (13 males, 4 females, average age 27.9 years), all with no history of neurological or muscular disorders. The experiment induced kinesthetic illusion through visual stimulation and recorded changes in the soleus muscle’s Hoffmann reflex (H-reflex). Two control conditions were set: one with visual stimulation without kinesthetic illusion and another with a static foot image as a rest condition.

2. Experimental Setup and Visual Stimulation

The experiment used a system to play pre-recorded foot movement videos and deliver electrical stimulation to peripheral nerves. The video content included ankle dorsiflexion and plantarflexion movements, each lasting 3 seconds. The video was displayed on a liquid crystal display (LCD), with the monitor’s position adjusted to align with the participant’s actual foot position to induce kinesthetic illusion.

3. Electrophysiological Recording and Stimulation

During the experiment, the H-reflex was evoked by electrical stimulation of the tibial nerve, and surface electromyography (sEMG) of the soleus muscle was recorded. To assess reciprocal inhibition and presynaptic inhibition, conditional stimulation of the common peroneal nerve (CPN) was also used. The experiment controlled video playback and nerve stimulation triggers using LabVIEW software.

4. Data Analysis

The amplitude of the H-reflex was calculated using the peak-to-peak measurement method and normalized to the maximum H-reflex amplitude (H-max). The experimental data were statistically compared using repeated-measures analysis of variance (ANOVA), with post hoc analysis conducted using the Bonferroni test.

Key Findings

1. Unconditioned H-reflex

In the measurement of the unconditioned H-reflex, no significant differences were observed among the visual stimulation conditions (kinesthetic illusion, no illusion, and rest conditions; p = 0.402). This indicates that kinesthetic illusion itself did not directly alter the monosynaptic reflex of the soleus muscle.

2. Reciprocal Inhibition (IA Inhibition)

In the measurement of reciprocal inhibition, the H-reflex amplitude under the kinesthetic illusion condition was significantly lower than that under the no-illusion and rest conditions (p = 0.002). This suggests that kinesthetic illusion enhances reciprocal inhibition, thereby suppressing the monosynaptic reflex of the soleus muscle.

3. Presynaptic Inhibition (D1 Inhibition)

In the measurement of presynaptic inhibition, the H-reflex amplitude under the kinesthetic illusion condition was also significantly lower than that under the no-illusion and rest conditions (p = 0.001). This indicates that kinesthetic illusion enhances presynaptic inhibition, further suppressing the monosynaptic reflex of the soleus muscle.

Conclusions and Significance

This study demonstrates that visually induced kinesthetic illusion can suppress the monosynaptic reflex of the soleus muscle by enhancing reciprocal inhibition and presynaptic inhibition in the spinal cord. This finding reveals the neural mechanisms of kinesthetic illusion at the spinal level, providing theoretical support for its clinical application in rehabilitation. In particular, kinesthetic illusion may modulate spinal inhibitory circuits to suppress spasticity, offering a new approach for the rehabilitation of stroke patients.

Research Highlights

1. Revealing Neural Mechanisms: This study is the first to reveal the neural mechanisms by which visually induced kinesthetic illusion modulates monosynaptic reflexes through spinal inhibitory circuits.
2. Potential Clinical Applications: The findings provide a theoretical basis for the application of kinesthetic illusion in the treatment of spasticity in stroke patients, highlighting its clinical significance.
3. Innovative Experimental Design: The study combines visual stimulation and electrophysiological recording to design a novel experimental system, offering a reference for future related research.

Additional Valuable Information

The visual stimulation system and electrophysiological recording methods used in the study were independently developed, showcasing high innovation. Additionally, the study validated the effects of kinesthetic illusion on spinal inhibitory circuits through detailed statistical analysis, providing important data support for future neuroscientific research.

This study not only deepens our understanding of the neural mechanisms of kinesthetic illusion but also offers new ideas and methods for clinical rehabilitation.