Accommodation and pupilloconstriction areas in the cat midbrain.

The results of our previous studies suggest that the rostral superior colliculus (SC) is involved in the control of accommodation in the cat. The accommodation-related area in the rostral SC projects into the pretectum and the mesencephalic reticular formation (MRF), indicating that these areas may also be involved in the control of accommodation. In this study, we tried to identify cat midbrain areas of accommodation and pupilloconstriction control by systematically mapping microstimulation responses. Three regions were found to evoke the accommodation response: the posterolateral pretectum, including the nucleus of the optic tract and the posterior pretectal nucleus; the posteromedial pretectum, including the nucleus of the posterior commissure (NPC) and adjacent commissural fibers; and the MRF area dorsolateral to the oculomotor nucleus. Pupilloconstriction was evoked by microstimulation of the posteromedial pretectum around the NPC and the anterior pretectum around the olivary pretectal nucleus.