Magnetically recorded oscillatory responses to luminance stimulation in man

Fast-frequency (ca. 100–110 Hz) oscillatory potentials superimposed on waves N2 and P2 of conventional broad-band VEP were magnetically recorded in man from occipital locations in response to monocular transient flash stimulation with full-field flashes (3.5 cd s⁻¹ m⁻² intensity) and in spots (1, 1.5, or 2.0 cm in diameter). These oscillations proved replicable between- and within-subject and were phase-locked to retinal oscillatory potentials, with maximum correlation at approximately 35 ms and mean delay (as measured between the first measurable peaks) of 27.4±1.6 ms. When stimuli were in spots at increasing eccentricity (5, 15, or 25°) from foveal fixation, broad-band VEP were recorded regardless of diameter and eccentricity of spot, whereas oscillatory responses were not detectable at eccentricity of, or greater than, 15°. This observation suggests that broad-band VEP and the oscillatory response are generated by (partly) distinct neuronal populations and/or functional arrangements and that there is some functional connection between cortical oscillatory responses and stimulus-related events triggered in central retina.