A Novel Tectal/Pretectal Population of Premotor Lens Accommodation Neurons

Abstract

Purpose Under real-world conditions, saccades are often accompanied by changes in vergence angle and lens accommodation that compensate for changes in the distance between the current fixation point and the next target. As the superior colliculus directs saccades, we examined whether it contains premotor neurons that might control lens compensation for target distance. Methods Rabies virus or recombinant rabies virus was injected into the ciliary bodies of Macaca fascicularis monkeys to label circuits controlling lens accommodation via retrograde transsynaptic transport. In addition, conventional anterograde tracers were used to confirm the rabies findings with respect to projections to preganglionic Edinger–Westphal motoneurons. Results At time courses that rabies virus labeled lens-related premotor neurons in the supraoculomotor area and central mesencephalic reticular formation, labeled neurons were not found within the superior colliculus. They were, however, found bilaterally in the medial pretectal nucleus continuing caudally into the tectal longitudinal column, which lies on the midline, between the colliculi. A bilateral projection by this area to the preganglionic Edinger–Westphal nucleus was confirmed by anterograde tracing. Only at longer time courses were cells labeled in the superior colliculus. Conclusions The superior colliculus does not provide premotor input to preganglionic Edinger–Westphal nucleus motoneurons, but may provide input to lens-related premotor populations in the supraoculomotor area and central mesencephalic reticular formation. There is, however, a novel third population of lens-related premotor neurons in the tectal longitudinal column and rostrally adjacent medial pretectal nucleus. The specific function of this premotor population remains to be determined.

Neurophysiology of gaze orientation: Core neuronal networks

“…In summary, the knowledge of the detailed neuronal circuitry underlying the generation of disjunctive eye movements is not advanced as much as the circuitry for conjugate saccades (Mays and Gamlin, 1995a, b) but a lot of progress has been made during the last decade (e.g., May et al, 2022). Soon it will be possible to understand the complex neurophysiology that underlies the generation of vergence eye movements and their dysfunction (Das 2016;Lennerstrand 2007).…”