Localization of the optic tract by using subcortical visual evoked potentials (VEPs) in cats

Objectives: This study was aimed to clarify the relationship between the amplitudes of visual evoked near field potentials and distance from the optic tract, and to determine the adequate filter settings to record these potentials from the optic tract separately from the far field potentials. Methods: The visual evoked near field potentials from the optic tract were consecutively recorded through intracerebral electrodes in 6 catsʹ brains. Different filter settings were tried and the amplitudes of visual evoked potentials (VEPs) were compared with the distance from the optic tract. Results: The filter settings of 100 Hz to 1 kHz were the best to obtain only the near field potentials separately from the far field potentials. Histological sections revealed that the potentials of the surface of the optic tract showed sudden increase of amplitude, above the 50% of the maximum VEPs amplitudes. Conclusions: The optic tract can be identified using these methods. These results can be applied to localize the optic tract during such an operative procedure as postero-ventral pallidotomy.