Cortical and subcortical pathways for pupillary reactions in rabbits.

Recordings of the unitary discharges from the ciliary nerves of rabbits indicated the presence of "ON" and "OFF" units, respectively exhibiting excitation or inhibition in response to ipsilateral diffuse light stimuli. The degree of both responses depended on the intensities of the light stimuli. The responses of both units were not evoked by electrical stimulation of the cervical sympathetic nerve, nor did they disappear when the sympathetic nerve was blocked. Thus, both units were thought to belong to the parasympathetic nerves originating from the oculomotor nerve. The spike discharges were recorded from both "ON" and "OFF" units of the ciliary nerves after electrical stimulation of the contralateral pretectal region. The latency of the responses ranged from 18 to 37 msec with a mean of 25 msec in the "ON" units, and 18 to 39 msec with a mean of 27 msec in the "OFF" units. The spike discharges were also evoked in both "ON" and "OFF" units by electrical stimulation of a defined area of the contralateral visual cortex; electrical stimulation of this area induced a pupil constriction in the contralateral eye, hence the area was called the cortical pupilloconstrictor area. The latency of the discharges was longer by 5 to 15 msec than the latency after the pretectal stimulation. It was thought that the impulses from the cortical pupilloconstrictor area are conducted via the pretectal region to the ciliary nerves, and that the pupillary light reflex and cortical pupillary response share a common pathway in the ciliary nerve.