Do the Pretectum and Accessory Optic System Play Different Roles in Optokinetic Nystagmus?

Abstract

Recent studies in birds and lower mammals have implicated the accessory optic system (AOS) and NOT in the generation of slow eye movements, especially OKN (reviewed by Simpson 1984). Single units in these structures respond to both the direction and velocity of full-field visual stimuli, and lesions of these structures compromise OKN. Both the AOS, which consists of lateral, medial, and dorsal terminal nuclei (LTN, MTN, DTN), and the NOT receive direct retinal input from the contralateral eye. Single units in the LTN and MTN prefer vertical visual motion (Simpson et al. 1979; Grasse and Cynader 1982, 1984; Mustari et al. 1986) whereas those in the DTN and NOT prefer horizontal visual motion (Grasse and Cynader 1984; Collewijn 1975; Hoffmann and Schoppmann 1981; Hoffmann and Distler 1986; Mustari and Fuchs 1988). One pathway by which the AOS and NOT could influence eye movements is via a projection to that part of the inferior olive (IO), the dorsal cap of Kooy, that supplies climbing fibers to the flocculus (Maekawa and Simpson 1973). The flocculus is known to have a role in smooth-pursuit (Lisberger and Fuchs 1978) and optokinetic (Zee et al. 1981; Waespe et al. 1985) eye movements.