title: Asymmetries in vestibular evoked myogenic potentials in chronic stroke survivors with spastic hypertonia: evidence for a vestibulospinal role.
abstract: OBJECTIVE
  Indirect evidence suggests that lateralized changes in motoneuron behavior post-stroke are potentially due to a depolarizing supraspinal drive to the motoneuron pool, but the pathways responsible are unknown. In this study, we assessed vestibular evoked myogenic potentials (VEMPs) in the neck muscles of hemispheric stroke survivors with contralesional spasticity to quantify the relative levels of vestibular drive to the spastic-paretic and contralateral motoneuron pools.
  
  
  METHODS
  VEMPs were recorded from each sternocleidomastoid muscle in chronic stroke survivors. Side-to-side differences in cVEMP amplitude were calculated and expressed as an asymmetry ratio, a proxy for the relative amount of vestibular drive to each side.
  
  
  RESULTS
  Spastic-paretic VEMPs were larger than contralateral VEMPs in 13/16 subjects. There was a strong positive relationship between the degree of asymmetry and the severity of spasticity in this subset of subjects. Remaining subjects had larger contralateral responses.
  
  
  CONCLUSIONS
  Vestibular drive to cervical motoneurons is asymmetric in spastic stroke survivors, supporting our hypothesis that there is an imbalance in descending vestibular drive to motoneuron pools post-stroke. We speculate this imbalance is a consequence of the unilateral disruption of inhibitory corticobulbar projections to the vestibular nuclei.
  
  
  CONCLUSIONS
  This study sheds new light on the underlying mechanisms of post-stroke spasticity.
authors.affiliation: Northwestern University Interdepartmental Neuroscience Program, Northwestern University, Chicago, IL 60611, USA; Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL 60611, USA. Electronic address: derek@u.northwestern.edu.
authors.forename: Derek M
authors.initials: DM
authors.lastname: Miller
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL 60611, USA.
authors.forename: Cliff S
authors.initials: CS
authors.lastname: Klein
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL 60611, USA.
authors.forename: Nina L
authors.initials: NL
authors.lastname: Suresh
authors.affiliation: Northwestern University Interdepartmental Neuroscience Program, Northwestern University, Chicago, IL 60611, USA; Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL 60611, USA.
authors.forename: William Z
authors.initials: WZ
authors.lastname: Rymer
mesh_terms: D000328:Adult; D000368:Aged; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D009128:Muscle Spasticity / Q000209:etiology / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D011712:Pyramidal Tracts / Q000503:physiopathology*; D012720:Severity of Illness Index; D020521:Stroke / Q000150:complications / Q000503:physiopathology*; D017741:Survivors; D058585:Vestibular Evoked Myogenic Potentials / Q000502:physiology*; D014726:Vestibular Nuclei / Q000503:physiopathology*
keywords: Chronic stroke subjects; Hemispheric stroke; Human; Motoneuron; Post-stroke spasticity; Vestibular evoked myogenic potentials; Vestibulospinal