Transection of the basal optic root in the frog abolishes vertical optokinetic head-nystagmus.

Bilateral disruption, or one-sided transection of the basal optic root with a partial injury of this tract of retinal fibres on the other side, abolished vertical, but spared horizontal optokinetic head-nystagmus. Horizontal nystagmus could not be evoked when the ventral part of the pretectum was injured and the basal optic root was transected on the same side. The lesions were checked by the cobalt-filling technique. It is concluded that the basal optic nucleus mediates stimuli which evoke vertical optokinetic head-nystagmus in frogs.