Walsh & Hoyt: Excitatory Influences of Visual Cortex on the Pupil Light and Near Reflexes

In addition to the classic midbrain afferent pathway to the pupillomotor center, a second important excitatory influence on the pupillary constrictor neurons in the visceral nuclei of the oculomotor complex arrives via centrifugal pathways from the occipital cortex. These excitatory pathways almost certainly follow the same general route to the midbrain as the occipital motor pathways to somatic components of the oculomotor complex. Some of these centrifugal fibers appear to modulate pupil constriction to near stimuli and are distributed in a more ventrolaterally location in the upper midbrain compared with the light reflex pathways, as evidenced by their relative invulnerability to midline lesions in the region of the tectum or posterior commissure. Indeed, the supranuclear pathways for pupillary constriction associated with voluntary or involuntary effort to look at a near object are unaffected by many pretectal lesions that interrupt the pupillary light reflexes, producing a dissociation between the amplitude of the light and near reflexeslight-near pupillary dissociation.