Visual evoked potentials to light flash in cats: is a frontal sinus reference electrode truly indifferent?
In flaxedilized cats, visual cortex evoked potentials (VEPs) to an intensity series of brief light flashes were recorded differentially using either a screw over frontal sinus or an insect pin in neck muscle as the reference electrode. At the same time EPs from the cornea (the ERG) and frontal sinus were recorded differentially against the neck muscle electrode. The EP recorded from the frontal sinus screw was a miniature of the ERG recorded from the cornea, with the same latencies and shape as the ERG but only 10-30% of its amplitude. At a fast presentation rate (1/sec) the amplitude of the ERG, and consequently the frontal sinus potential, decreased with increasing intensity of light flash, whereas at a slow presentation rate (1/3 or 1/5 sec) the ERG and frontal sinus potential increased in response to all but the highest intensities. The location of the reference electrode and the rate of light flash presentation had the following effects on visual cortex EP amplitudes. A frontal sinus reference increased the amplitudes of early components (less than 100 msec) of the VEP. Also, VEP amplitudes as a function of flash intensity yielded slopes which tended to be positive at a slow presentation rate and negative at a fast presentation rate. This effect is in accord with the rate dependent slopes of the frontal sinus potential.
D000818:Animals; D001522:Behavior, Animal; D002415:Cats; D003315:Cornea / Q000502:physiology; D004569:Electroencephalography; D004596:Electroretinography; D005074:Evoked Potentials, Visual; D005260:Female; D005626:Frontal Sinus / Q000502:physiology*; D008297:Male; D010775:Photic Stimulation / Q000379:methods