Fig 5. Model for the generation of night blindness–associated congenital nystagmus.

(A) wt ON-DSGCs (“GC”) signal direction of global image motion to the AOS. In the AOS, the ON-DSGC signals are integrated (“Σ”), and a compensatory eye movement is induced. In the dark, nob ON-DSGC spiking activity oscillates, but these oscillations are asynchronous. The integrated inputs to the AOS from asynchronous oscillating nob ON-DSGCs do not generate a signal sufficient to trigger an eye movement. In the presence of a stimulus-containing contrast, the oscillations of nob ON-DSGCs are synchronized, and their integrated input to the AOS oscillates, representing a significant retinal slip signal, and hence, a compensatory eye movement is induced. This eye movement will evoke a light response and keeps the GCs synchronized. The result is a pendular nystagmus. (B) A vertical grating oscillating horizontally over the retina effectively activates GCs, since the stimulus changes within the receptive field of the GC (circle) and keeps the GCs synchronized. A horizontal grating oscillating horizontally over the retina is ineffective in inducing a response in retinal neurons, since the stimulus will not change within the receptive field of the neurons (circle) and hence GCs will not be synchronized and thus no pendular nystagmus will occur. AOS, accessory optic system; GC, ganglion cell; ON-DSGC, ON direction-selective GC; wt, wild type.