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Galvanic vestibular stimulation alters the onset of motor unit discharge
Author(s) -
Kennedy Paul M.,
Cresswell Andrew G.,
Chua Romeo,
Inglis J. Timothy
Publication year - 2004
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.20074
Subject(s) - galvanic vestibular stimulation , isometric exercise , motor unit , stimulation , reflex , neuroscience , vestibular system , spinal cord , stimulus (psychology) , h reflex , electromyography , medicine , physical medicine and rehabilitation , anatomy , psychology , psychotherapist
We have previously shown that galvanic vestibular stimulation (GVS) can modulate the amplitude of the passive soleus H‐reflex. This study examined whether the response resulted from a general change in excitability of the motoneuron pool or a specific modulation of individual motor units (MUs). Subjects performed slow isometric plantarflexor actions in a prone lying and kneeling position until the discharge of a single gastrocnemius MU was detected. During randomly selected trials, a 1‐mA bipolar, binaural galvanic stimulus was triggered just prior to the start of plantarflexor activity. With the knee extended and the medial gastrocnemius (MG) at a long muscle length, GVS did not have an effect on MU activity. However, when the knee was flexed and the MG muscle was shortened, GVS significantly modified the onset of activation and the initial firing frequency of MUs. This may reflect a change in the gain of the presynaptic inhibitory mechanisms that act on the motoneuron pool once a muscle reaches a shortened, nonoptimal force‐producing length. Thus, GVS may provide an important research tool for activating descending vestibulospinal pathways that act on lower‐limb motoneurons and may be applied to test the integrity of the spinal cord. Muscle Nerve 188–194, 2004