Visual-evoked potentials in cats, using a light-emitting diode stimulator.

Visual-evoked potentials (VEP) were studied in 8 healthy adult cats anesthetized with xylazine HCl and ketamine HCl. Monocular visual stimulation was accomplished by a 3 x 5 matrix of light-emitting diodes. Subcutaneous needle electrodes placed in the scalp at various locations and a contact lens electrode on the cornea were used to record cortical and electroretinographic activities, respectively. Multiple electrode pairings and unilateral optic nerve transsection were used to distinguish between retinal and postretinal potentials recorded from scalp electrodes. The VEP was a robust polyphasic cortical potential, with peak latencies between 0 and 110 ms. Using the light-emitting diode method of stimulation, a VEP was recorded which was not contaminated by volume-conducted retinal activity.