## 4 Discussion  
Sensory impairment is a great contributor to movement disfunction and postural instability in [PERSON]'s disease. While healthy subjects mainly rely on somatosensory information to maintain an upright posture, these individuals show an increased reliance on visual cues [18]. A study of [PERSON] et al. [8] demonstrated that PD patients experience significantly greater variations in center of pressure (CoP) while performing stabilometric analyses with the eyes closed. Our results are in agreement with the study of [PERSON] as the results showed a greater postural instability during static tests performed with closed eyes. After application of focal vibration, a progressive reduction of the oscillation velocity on the x-axis, oscillation area with closed eyes and Romberg ratio were observed between T0 and T2. Moreover, a slight improvement of the Tinetti score was observed from T0 to T2 with a statistically significant difference at T1. This seems to suggest a beneficial role of focal vibration on proprioception and a decreased need of reliance on visual cues both during free stance and during motion associated with usual exercises. Focal muscle vibration works by conveying repetitive proprioceptive and exteroceptive stimuli from peripheral musculocutaneous mechanoreceptors up to the ventral posterolateral nucleus of the thalamus and to the primary domestic areas of the cerebral cortex [10]. Studies on brain excitability performed under positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have shown significant activation of the motor cortex during muscle vibration [11, 12]. Moreover, experiments performed with transcranial magnetic stimulation (TMS) have demonstrated a facilitation of the muscular \begin{table}
\begin{tabular}{c c c c c} \hline \hline (**Mean and SD**) & **T0** & **T1** & **T2** & \(p\) **Value** \\ \hline
**Tinetti** & 23.00 \(\pm\) 1.84 & **24.19 \(\pm\) 1.74 \({}^{*}\)** & 24.60 \(\pm\) 2.18 & 0.000 \\
**Velocity x axis CE** & 26.03 \(\pm\) 12.1 & 27.05 \(\pm\) 17.80 & **22.10 \(\pm\) 14.01 \({}^{*}\)** & 0.006 \\
**(mm/s)** & 563.36 \(\pm\) 340.02 & 509.15 \(\pm\) 428.10 & **428.57 \(\pm\) 342.64 \({}^{*}\)** & 0.006 \\
**Romberg Area** & 319.04 \(\pm\) 179.72 & 303.89 \(\pm\) 187.02 & **224.68 \(\pm\) 124.09 \({}^{*}\)** & 0.05 \\ \hline \hline \end{tabular} \({}^{*}\)\(p\) level \(\leq\) 0.05 was considered statistically significant with Student’s-test for paired samples.  
\end{table} 
Table 2: Tinetti score and significant stabilometric scores. electrical response (MEP) and a modulation of intracortical inhibition, proving that pure sensory stimulation is able to influence the motor response [12]. In recent years, several studies have tested a novel proprioceptive focal vibration device (Equistasi(r)) consisting of a self-wearable patch, applied over the cervical spine that produces a 300 Hz vibration from body heat. This system has proven to be effective at improving posture, stability and quality of gait in moderate Parkinson's patients [7; 9; 18; 19]. Compared to these studies, our protocol differs as it used a pneumatic vibration device (EVM, Endomedica, Rome, Italy) applied to the upper back and lower limb muscles. The choice of the vibration targets was based on our clinical judgment while the frequency and amplitude parameters were chosen according to the most commonly applied parameters in literature [11]. Despite the differences in site of application and frequency between the studies, in both cases, focal vibration has shown to work effectively in postural control and gait disorders in PD patients. A common criticism toward the use of focal vibration is that it is not clear how long the effects last after a treatment; some authors suggest that the effect is quickly lost as soon as the treatment is withdrawn while others reported visible effects even after weeks from the last application [12].