Alterations of neuromuscular signals as a result of vestibular stimulation

Interest in a better understanding of mechanical vestibular stimulation and its effect on changing the muscle tone in individuals with Cerebral Palsy (CP) is the motivation of this study. Stimulation to the otoliths has shown a reduction in the degree of spasticity in population with neuromuscular disabilities. Three children with CP were involved in this study of whom two are twins (12 year-old, female) and the third is a 14-year old, male. The pendulum knee drop (PKD) test was used to evaluate the degree of subject´s spasticity. The vestibular stimulation consisted of vertical oscillation with 3 inches of amplitude, a frequency of 2 Hz and a 15 minute duration. This form of stimulation targets the saccule organ in the vestibular system, which results in alteration of the descending signals of the vestibular system responsible for setting tone of the antigravity muscles. Electromyography (EMG) is simultaneously recorded from the quadriceps (Vastus Lateralis) and hamstring (Biceps Femoris) muscles along with the PKD test. The activation of EMG during PKD can be understood in relationship to the flexion and extension of the lower leg. It is interesting that EMG activity for quadriceps is seen at every flexion cycle in the post stimulation data, while on the other hand EMG activity is nearly continuous in the initial cycles of PKD in the pre stimulation. This may be an indication of a change in the activation pattern of EMG from the agonist and antagonist muscles as a result of the vestibular stimulation, which causes neural changes in the vestibular descending signal. In all three subjects of this study, the knee stiffness and damping parameters show a dramatic decrease post vestibular stimulation, and a smaller change is also noticed in the parameter describing virtual trajectory.