title: Contributions of motoneuron hyperexcitability to clinical spasticity in hemispheric stroke survivors.
abstract: OBJECTIVE
  Muscle spasticity is one of the major impairments that limits recovery in hemispheric stroke survivors. One potential contributing mechanism is hyperexcitability of motoneurons. Previously, the response latency of the surface electromyogram (EMG) record evoked by joint rotation has been used to characterize motoneuron excitability. Given the limitations of this method, the objective of the current study was to reexamine the excitability of motoneurons in chronic stroke survivors by estimating reflex latency using single motor unit discharge.
  
  
  METHODS
  We quantified the excitability of spastic motoneurons using the response latency of a single motor unit discharge elicited by a position controlled tap on the biceps brachii tendon. We applied tendon taps of different amplitudes on the biceps tendons of both arms of the stroke survivors. Unitary reflex responses were recorded using intramuscular EMG recordings.
  
  
  RESULTS
  Our results showed that the latency of unitary discharge was systematically shorter in the spastic muscle compared with the contralateral muscle, and this effect was consistent across multiple tap amplitudes.
  
  
  CONCLUSIONS
  This method allowed us to quantify latencies more accurately, potentially enabling a more rigorous analysis of contributing mechanisms.
  
  
  CONCLUSIONS
  The findings provide evidence supporting a contribution of hyperexcitable motoneurons to muscle spasticity.
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA. Electronic address: xiaogang.hu@northwestern.edu.
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Hu
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA.
authors.forename: Nina L
authors.initials: NL
authors.lastname: Suresh
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA.
authors.forename: Matthieu K
authors.initials: MK
authors.lastname: Chardon
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
authors.forename: William Z
authors.initials: WZ
authors.lastname: Rymer
mesh_terms: D000368:Aged; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D009128:Muscle Spasticity / Q000209:etiology / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D020521:Stroke / Q000150:complications / Q000503:physiopathology*
keywords: Hyperexcitability; Motoneuron excitability; Reflex latency; Spasticity; Tendon tap