Optimal check size and reversal rate to elicit pattern-reversal MEG responses.
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.
Chen
Wei-Ta
WT
Neurological Institute, Taipei Veterans General Hospital, Taiwan.
Ko
Yu-Chieh
YC
Liao
Kwong-Kum
KK
Hsieh
Jen-Chuen
JC
Yeh
Tzu-Chen
TC
Wu
Zin-An
ZA
Ho
Low-Tone
LT
Lin
Yung-Yang
YY
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