Alternate trains of postural muscle vibration promote cyclic body displacement in standing parkinsonian patients

Patients suffering from Parkinson's disease (PD) have difficulties with control of stance, postural changes, and walking, seemingly depending on problems in central integration of proprioceptive information. We tested the hypothesis that alternate vibration of postural muscles can induce cyclic medio-lateral or antero-posterior sway in PD, mimicking that accompanying body progression during walking, thereby favoring the production of locomotor tasks. In 12 standing PD patients and 11 healthy subjects, we applied trains of vibratory stimuli, bilaterally in an alternating paradigm to soleus, tibialis anterior, or paravertebral muscles. The trains of stimuli were delivered at frequencies selected to be above, near, and below the normal walking rhythm. The displacement of the center of foot pressure (CoP) was recorded. In PD, sway area during unperturbed stance was just larger than in healthy subjects; shifts in CoP in response to vibration were preserved, regardless of the vibrated muscle pair; CoP oscillations along medio-lateral, but not antero-posterior direction, were coupled to the vibration trains; time to initiate and terminate the postural responses was normal. PD patients correctly integrate and exploit the vibration-induced proprioceptive inflow to produce body oscillations comparable to those occurring during walking. Vibratory stimulation can be safely and easily employed to provoke rhythmic postural changes in PD.