Binocular interactions in the dorsal lateral geniculate nucleus of monocularly paralyzed cats: extraretinal and retinal influences.

Abstract

Prolonged periods of monocular paralysis alter the physiology of the dorsal lateral geniculate nucleus (LGN), shifting the X/Y cell ratio so that X cells are encountered less frequently than Y cells. The shift in the LGN X/Y cell ratio is observed in both the A-layers of both geniculates whether the innervating eye is paralyzed or mobile. This change in the LGN has been attributed to a mechanism that is sensitive to disruptions in binocular cues. The effects of monocular paralysis in the LGN were used to demonstrate that LGN cells possess a sensitivity to binocular cues of an extraretinal and retinal source. The removal of extraretinal signals, in the form of proprioceptive feedback from the extraocular muscles of the mobile eye, by section of the ophthalmic branch of the Vth cranial nerve, resulted in an immediate and long-lasting reversal in the effects of monocular paralysis. The LGN X/Y ratio was restored to a normal value in the layers innervated by the eye with intact proprioceptive inputs as well as in the layers innervated by the eye in which proprioceptive inputs were removed. In contrast to this, the removal of proprioceptive inputs from the paralyzed eye had no effect on the LGN X/Y ratio. The removal of visual inputs from the mobile eye by section of the optic nerve resulted in an immediate, but somewhat transient reversal in the effects of monocular paralysis. Within the first 25 h after optic nerve section, the LGN X/Y ratio was restored to a normal value in the layers innervated by the eye with intact visual inputs. A transient reversal was also observed when both visual and proprioceptive inputs from the mobile eye were removed. These results are consistent with the belief that the LGN is one site in the visual pathway where proprioceptive and visual signals from the two eyes converge.