title: Inter-individual variation in reciprocal Ia inhibition is dependent on the descending volleys delivered from corticospinal neurons to Ia interneurons.
abstract: BACKGROUND
  We investigated the extent to which the corticospinal inputs delivered to Ia inhibitory interneurons influence the strength of disynaptic reciprocal Ia inhibition.
  
  
  METHODS
  Seventeen healthy subjects participated in this study. The degree of reciprocal Ia inhibition was determined via short-latency (condition-test interval: 1-3ms) suppression of Sol H-reflex by conditioning stimulation of common peroneal nerve. The effect of corticospinal descending inputs on Ia inhibitory interneurons was assessed by evaluating the conditioning effect of transcranial magnetic stimulation (TMS) on the Sol H-reflex. Then, we determined the relationship between the degree of reciprocal Ia inhibition and the conditioning effect of TMS on the Sol H-reflex.
  
  
  RESULTS
  We found that the degree of reciprocal Ia inhibition and the extent of change in the amplitude of the TMS-conditioned H-reflex, which was measured from short latency facilitation to inhibition, displayed a strong correlation (r=0.76, p<0.01) in the resting conditions.
  
  
  CONCLUSIONS
  The extent of reciprocal Ia inhibition is affected by the corticospinal descending inputs delivered to Ia inhibitory interneurons, which might explain the inter-individual variations in reciprocal Ia inhibition.
authors: Human Motor Control Laboratory, Department of Human Sciences, Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan.
authors: Shinji
authors: S
authors: Kubota
authors: Human Motor Control Laboratory, Department of Human Sciences, Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan; Research Fellow of the Japan Society for the Promotion of Science, Tokyo, Japan.
authors: Kazumasa
authors: K
authors: Uehara
authors: Human Motor Control Laboratory, Department of Human Sciences, Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan; Research Fellow of the Japan Society for the Promotion of Science, Tokyo, Japan.
authors: Takuya
authors: T
authors: Morishita
authors: Human Motor Control Laboratory, Department of Human Sciences, Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan.
authors: Masato
authors: M
authors: Hirano
authors: Human Motor Control Laboratory, Department of Human Sciences, Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan. Electronic address: funase@hiroshima-u.ac.jp.
authors: Kozo
authors: K
authors: Funase
mesh_terms: D000328:Adult; D003213:Conditioning, Psychological / Q000502:physiology; D004558:Electric Stimulation; D004576:Electromyography; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D007395:Interneurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation*; D009433:Neural Inhibition / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D011712:Pyramidal Tracts / Q000166:cytology* / Q000502:physiology; D012016:Reference Values; D055366:Synaptic Potentials / Q000502:physiology; D013979:Tibial Nerve / Q000502:physiology; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: Corticospinal tract; Individual variation; Reciprocal Ia inhibition; Spinal cord; Synaptic plasticity