title: Human corticospinal excitability in microgravity and hypergravity during parabolic flight.
abstract: BACKGROUND
  Spontaneous electromyographic (EMG) activity in the soleus muscle of the rat varies with the changing gravitational force in parabolic flight, presumably in an appropriate way to resist the load. We investigated how decreased and increased gravitational force affects EMG in human back and arm muscles and to what extent the motor cortex is responsible for any modulation seen.
  
  
  METHODS
  Three healthy subjects stood during 10 parabolas consisting of periods (duration 20-25 s) of 1.8 G, then 0 G, and then 1.8 G. EMG recordings were made from right deltoid and left and right erector spinae (ES) muscles and transcranial magnetic stimulation (TMS) was applied to the motor cortex to produce motor evoked potentials (MEPs) in target muscles.
  
  
  RESULTS
  In one exemplary subject, EMG levels and MEP areas increased in the left ES and right ES during periods of 0 G, which was less pronounced with the arm abducted. No significant changes were seen in EMG levels or MEP areas during periods of 1.8 G. Pooled data from the three subjects showed a similar pattern, revealing a facilitation of MEP responses in left and right ES muscles in periods of 0 G.
  
  
  CONCLUSIONS
  EMG levels and MEP areas in ES muscles increased during periods of 0 G, suggesting that back muscle activity is "turned on" to stabilize the axial skeleton when the vertical compression forces present on Earth are removed. Further analysis suggested that microgravity produced activation of ES muscles through an increase in corticospinal excitability.
authors.affiliation: Department of Sensorimotor Systems, Division of Neuroscience & Psychological Medicine, Imperial College London, Charing Cross Hospital, London, UK. n.davey@imperial.ac.uk
authors.forename: Nick J
authors.initials: NJ
authors.lastname: Davey
authors.forename: Steve R
authors.initials: SR
authors.lastname: Rawlinson
authors.forename: Alex V
authors.initials: AV
authors.lastname: Nowicky
authors.forename: Alison H
authors.initials: AH
authors.lastname: McGregor
authors.forename: Kitsou
authors.initials: K
authors.lastname: Dubois
authors.forename: Paul H
authors.initials: PH
authors.lastname: Strutton
authors.forename: Robert C
authors.initials: RC
authors.lastname: Schroter
mesh_terms: D000054:Acceleration; D004576:Electromyography; D005260:Female; D006801:Humans; D018471:Hypergravity / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D011712:Pyramidal Tracts / Q000502:physiology*; D013026:Space Flight; D014893:Weightlessness / Q000009:adverse effects*