Pretectal region and the pupillary light reflex. An anatomical analysis in the monkey

Abstract The effects of discrete lesions in the pretectal region of the monkey upon the pupillary light reflex were studied, using infrared pupillography. Resulting degeneration was studied by silver impregnation methods. The nucleus of the optic tract (NOT) and the sublentiform nucleus (SL) project fibers to the nuclei of the posterior commissure (NPC) and to portions of the ipsilateral inferior pulvinar, pregeniculate nucleus and dorsal lateral geniculate body. NPC gives rise to the bulk of the fibers in the posterior commissure (PC) which largely terminate upon contralateral cells of NPC. Some fibers arising from NPC enter the ipsilateral central gray and terminate bilaterally primarily upon cells of the medial visceral columns of the oculomotor complex (OMC). These fibers partially decussate ventral to the aqueduct. Fibers from the olivary nucleus (ON) cross in the PC and project to terminations upon: (1) large cells of the opposite ON and (2) the anterior median nuclei and the contralateral lateral visceral cell column of OMC. NOT, and possibly ON, give rise to fibers crossing in PC that project to the contralateral accessory optic tract nucleus (AOTN). Unilateral lesions that fairly selectively destroy parts of NOT, ON, SL, NPC, central fibers of PC or the nucleus of the pretectal area (NPA), produce neither miosis, mydriasis, anisocoria, nor do they impair direct or consensual pupillary light reflexes. Unilateral lesions, which impair pupillary light reflexes, involve multiple structures, such as NPC, PC and lateral regions of the central gray.