Tone Burst-evoked Myogenic Potentials in Human Neck Flexor and Extensor

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Abstract
Vestibular evoked myogenic potential (VEMP) has been proposed to be a manifestation of sacculocollic reflex. In a recent study using intracellular recording from neck flexor and extensor motoneurons, the neuronal connections and pathways underlying sacculocollic reflexes were determined in cats. The results showed that sacculocollic reflex displayed inhibitory connection to bilateral neck flexors and excitatory connection to bilateral neck extensors. A total of 16 normal young adults were tested with bilateral recordings of sternocleidomastoid (SCM) and splenius capitis (SC) muscles by acoustic stimulus of 500 Hz short tone burst. The results revealed that polarity of the wave I/II of VEMP on SC was the reverse of that on SCM. This implied that VEMP from ipsilateral SCM showed inhibitory neural activity; whereas VEMP from ipsilateral SC was an excitatory response. Using this non-invasive technique, the sacculocollic reflexes in human neck flexor and extensor were studied. The results in humans were consistent with the previous findings in cats.