title: Phosphene thresholds correlate with paired-pulse suppression of visually evoked potentials.
abstract: BACKGROUND
  Phosphene thresholds (PT) induced by transcranial magnetic stimulation (TMS) as well as paired-pulse suppression (PPS) of visually evoked potentials (VEP) are used to characterize visual cortex excitability, however, their relation remains unknown.
  
  
  METHODS
  We measured PT after single TMS over the occipital lobe, and recorded VEPs after paired-pulse stimulation at short stimulus-onset-asynchronies in the same subject. PPS was expressed by the ratio second to first response.
  
  
  RESULTS
  We found a negative correlation between PT and PPS (r = -0.36, P = 0.039) indicating that higher PT were associated with smaller ratios indicative of low excitability, and vice versa. There was no difference in PPS between subjects who perceived phosphenes and those who did not.
  
  
  CONCLUSIONS
  Although both approaches target different mechanisms, PT and PPS seem to reflect common characteristics of visual cortex excitability. The lack of differences in PPS in subjects not perceiving phosphenes suggests that they might not have higher excitability levels.
authors.affiliation: Department of Neurology, Ruhr-University Bochum, BG-Universitätsklinikum Bergmannsheil, Bochum, Germany. oliver.hoeffken@ruhr-uni-bochum.de
authors.forename: Oliver
authors.initials: O
authors.lastname: Höffken
authors.forename: Melanie
authors.initials: M
authors.lastname: Lenz
authors.forename: Matthias
authors.initials: M
authors.lastname: Sczesny-Kaiser
authors.forename: Hubert R
authors.initials: HR
authors.lastname: Dinse
authors.forename: Martin
authors.initials: M
authors.lastname: Tegenthoff
mesh_terms: D000328:Adult; D001931:Brain Mapping; D004558:Electric Stimulation; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009778:Occipital Lobe / Q000502:physiology*; D010719:Phosphenes; D010775:Photic Stimulation; D050781:Transcranial Magnetic Stimulation