Focal vibrations enhance somatosensory facilitation in healthy subjects: A pilot study on Equistasi® and high-frequency oscillations

Bilateral median nerve stimulation and High-Frequency Oscillations unveil interhemispheric inhibition of primary sensory cortex

OBJECTIVE

This study aimed at investigating the effect of median nerve stimulation on ipsilateral cortical potentials evoked by contralateral median nerve electrical stimulation.

METHODS

We recorded somatosensory-evoked potentials (SEPs) from the left parietal cortex in 15 right-handed, healthy subjects. We administered bilateral median nerve stimulation, with the ipsilateral stimulation preceding the stimulation on the contralateral by intervals of 5, 10, 20, or 40 ms. We adjusted these intervals based on each individual's N20 latency. As a measure of S1 excitability, the amplitude of the N20 and the area of the High Frequency Oscillation (HFO) burst were analyzed for each condition.

RESULTS

The results revealed significant inhibition of N20 amplitude by ipsilateral median nerve stimulation at interstimulus intervals (ISIs) between 5 and 40 ms. Late HFO burst was suppressed at short ISIs of 5 and 10 ms, pointing to a transcallosal inhibitory effect on S1 intracortical circuits.

CONCLUSIONS

Findings suggest interhemispheric interaction between the primary somatosensory areas, supporting the existence of transcallosal transfer of tactile information.

SIGNIFICANCE

This study provides valuable insights into the interhemispheric connections between primary sensory areas and underscore the potential role of interhemispheric interactions in somatosensory processing.

High-frequency transcranial alternating current stimulation matching individual frequency of somatosensory evoked high-frequency oscillations can modulate the somatosensory system through thalamocortical pathway

tACS (transcranial alternating current stimulation) is a technique for modulating brain activity through electrical current. Its effects depend on cortical entrainment, which is most effective when transcranial alternating current stimulation matches the brain's natural rhythm. High-frequency oscillations produced by external stimuli are useful for studying the somatosensory pathway. Our study aims to explore transcranial alternating current stimulation's impact on the somatosensory system when synchronized with individual high-frequency oscillation frequencies. We conducted a randomized, sham-controlled study with 14 healthy participants. The study had three phases: Individualized transcranial alternating current stimulation (matching the individual's high-frequency oscillation rhythm), Standard transcranial alternating current stimulation (600 Hz), and sham stimulation. We measured early and late HFO components after median nerve electrical stimulation at three time points: before (T0), immediately after (T1), and 10 min after transcranial alternating current stimulation (T2). Compared to Sham and Standard stimulation Individualized transcranial alternating current stimulation significantly enhanced high-frequency oscillations, especially the early component, immediately after stimulation and for at least 15 min. No other effects were observed for other high-frequency oscillation measures. In summary, our study provides initial evidence that transcranial alternating current stimulation synchronized with an individual's high-frequency oscillation frequency can precisely and time-specifically modulate thalamocortical activity. These insights may pave the way for innovative, personalized neuromodulation methods for the somatosensory system.

Effects of a proprioceptive focal stimulation (Equistasi®) on reducing the biomechanical risk factors associated with ACL injury in female footballers

Introduction

Football presents a high rate of lower limb injuries and high incidence of Anterior Cruciate Ligament (ACL) rupture, especially in women. Due to this there is the need to optimize current prevention programs. This study aims to verify the possibility to reduce the biomechanical risk factors associated with ACL injury, through the application of proprioceptive stimulation by means of the Equistasi® device.

Methods

Ten elite female footballers were enrolled and received the device for 4 weeks (5 days/week, 1h/day). Athletes were assessed directly on-field at four time points: T0 and T1 (evaluation without and with the device), T2 (after 2 weeks), T4 (after 4 weeks) while performing two different tasks: Romberg Test, and four sidestep cutting maneuvers bilaterally. Seven video cameras synchronized with a plantar pressure system were used, thirty double colored tapes were applied on anatomical landmarks, and three dimensional coordinates reconstructed. Vertical ground reaction forces and center of pressure data were extracted from the plantar pressure insoles. Hip, knee, and ankle flexion-extension angles and moments were computed as well as abd-adduction joint torques. From the Romberg Test both center of pressure descriptive variables and frequency analysis parameters were extracted. Each variable was compared among the different time frames, T1, T2 and T4, through Friedman Test for non-parametric repeated measures (p<0.05); Wilcoxon Signed Rank Test was used for comparing variables between T0 and T1 (p<0.05) and across the different time frames as follows: T1-T2, T2-T4 and T1-T4.

Results

Statistically significant differences in both posturographic and biomechanical variables between the assessment at T0 and T1 were detected. Reduced hip and knee abduction torques were revealed in association with reduced both ground reaction forces and ankle dorsiflexion torque from T1 up to T4.

Discussion

The proprioceptive stimuli showed to have the potential to improve cutting biomechanics mainly with respect to the ligament and quadriceps dominance theories. Results of the present study, even if preliminary and on a small sample size, could be considered promising towards the inclusion of proprioceptive training in injury prevention programs.