History
Bickford et al. (1964) and subsequently Townsend and Cody, provided evidence for a short latency response in posterior neck muscles in response to loud clicks that appeared to be mediated by activation of the vestibular apparatus. These authors made the additional important observations that the response was generated from EMG (muscle) activity and that it scaled with the level of tonic activation. Subsequent work led to the suggestion that the saccule was the end organ excited.
In 1992 Colebatch and Halmagyi reported a patient with a short latency response to loud clicks studied using a modified recording site (the sternocleidomastioid muscles: SCM) and which was abolished by selective vestibular nerve section. Colebatch et al. (1994) described the basic properties of the response. These were: the response occurred ipsilateral to the ear stimulated, the click threshold was high, the response did not depend upon hearing (cochlear function) per se, it scaled in direct proportion to the level of tonic neck contraction, the response was small (although large compared to many evoked potentials) and required averaging, and only the initial positive-negative response (p13-n23 by latency) was actually vestibular-dependent. It was subsequently shown to be generated by a brief period of inhibition of motor unit discharge.
Read more about this topic: Vestibular Evoked Myogenic Potential
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