Modulation of the soleus H-reflex in prone human subjects using galvanic vestibular stimulation.
OBJECTIVE
To determine if vestibular-evoked modulation of the soleus H-reflex can be achieved in a muscle that is not being used for postural support.


METHODS
Ten healthy subjects lay prone while the right leg was supported. In this position soleus H-reflex amplitudes were measured with the head facing forward, coupled with ipsilateral monopolar monaural galvanic stimulation (anode or cathode). To evaluate the interval between the onset of the galvanic stimulus and tibial nerve stimulation, the timing was varied between 0 and 200 ms in 20 ms intervals. A two-way ANOVA and student's t-test was performed to compare the mean amplitudes of the test and conditioned H-reflexes.


RESULTS
Galvanic stimulation significantly modified the amplitude of the H-reflex in a prone lying subject (P<0.05). Furthermore, the peak inhibitory and facilitatory effect occurred when the galvanic vestibular stimulus was delivered 100 ms prior to the H-reflex stimulus.


CONCLUSIONS
The results of this study demonstrate that galvanic stimulation can modulate the excitability of the soleus motoneuron pool when the muscle is not being used posturally. This suggests that in certain situations, it may be possible to use this type of vestibular stimulation to examine the integrity of descending vestibulospinal pathways in prone human subjects.
Kennedy
P M
PM
School of Human Kinetics, The University of British Columbia, 210-6081 University Boulevard, British Columbia, V6T 1Z1, Vancouver, Canada.
Inglis
J T
JT
D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D016683:Supine Position; D014722:Vestibule, Labyrinth / Q000502:physiology*