In addition to light flux changes, it is well established that other stimulus attributes such as colour, spatial structure or movement can also cause a transient constriction of the pupil, even when the onset of the stimulus causes a net decrease in light flux level on the retina. Although experimental findings in human subjects with postgeniculate lesions show that the generation of such responses must involve the processing of stimulus attributes in extrastriate areas of the cortex, little is known about the site of integration of cortical signals into the pupillomotor pathway. We have investigated how visual performance and the various components of the pupil response have been affected in subjects with damage to the dorsal midbrain (Parinaud's syndrome). The results show that the probable destruction of the olivary pretectal nucleus and the nucleus of the optic tract has little or no effect on pupil grating or pupil colour responses. The light reflex response, on the other hand, is virtually abolished, with only a small residual component that is similar to the pupil grating response and may not require an afferent projection to the midbrain. These new findings suggest that the site of integration of cortical signals in relation to pupil colour and grating responses and the generation of sleepiness-induced oscillations of the pupil do not rely on the normal functioning of pretectal nuclei that are involved in the light reflex response.
