title: Optimal check size and reversal rate to elicit pattern-reversal MEG responses.
abstract: OBJECTIVE
  To determine the impact of check size and interstimulus interval (ISI) on neuromagnetic visual cortical responses.
  
  
  METHODS
  We recorded visual evoked fields to pattern-reversal stimulation with central occlusion in ten subjects. The -100 ms magnetic activation (P100m) was analyzed by single dipole modeling.
  
  
  RESULTS
  With 1 s ISI, P100m strengths increased as check size increased from 15' up to 120' of visual arc, and larger checks elicited less P100m activation. With 120' checks, we found no P100m attenuation as ISI decreased from 4 s to 0.16 s. P100m sources around the calcarine sulcus did not vary with check size or ISI.
  
  
  CONCLUSIONS
  The magnitude of cortical activation during visual contrast processing is check size-dependent and the 120' checks are optimum for future studies on neuromagnetic visual cortical functions using central-occluded stimulation. The corresponding neuronal activation demonstrated a short refractory period less than 0.16 s. We also found significantly overlapping cortical representation areas for different check sizes or ISIs.
authors: Neurological Institute, Taipei Veterans General Hospital, Taiwan.
authors: Wei-Ta
authors: WT
authors: Chen
authors: Yu-Chieh
authors: YC
authors: Ko
authors: Kwong-Kum
authors: KK
authors: Liao
authors: Jen-Chuen
authors: JC
authors: Hsieh
authors: Tzu-Chen
authors: TC
authors: Yeh
authors: Zin-An
authors: ZA
authors: Wu
authors: Low-Tone
authors: LT
authors: Ho
authors: Yung-Yang
authors: YY
authors: Lin
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology