The orienting ocular-following reflex in pretrigeminal cats with lesions of visual and oculomotor systems

The brain stem was transected in cats at the pretrigeminal level. Additional lesions were placed in 17 cats, whereas 10 served as controls without further manipulation. All received a small dose of amphetamine. The vertical following reflex was evoked by a slit of light or a black bar (1degrees X 4degrees). The stimuli moved along the vertical 'meridian or parall to it up to 40 degrees in the left or right hemifield. A unilateral removal of the superior colliculus produced a loss of reflexes evoked from the contralateral hemifield. In contrast, after unilateral ablation of the visual cortex only in one of 4 cats was the reflex from the contralateral hemifield smaller than ipsilaterally; and after unilateral ablation of the frontal oculomotor cortex, no hemifield asymmetry of these reflexes was found in any cat. The reflexes also survived bilateral ablation of the visual cortex or the frontal oculomotor cortex. After transection of the corpus callosum the reflexes were virtually normal. The data confirm that in the cat the orienting fixation reflex is mediated by the superior colliculus. On the other hand, this reflex appears to be largely independent of the cerebral cortex.