The effect of cerebellar and collicular lesions on the relative encounter rates for X and Y cells in the lateral geniculate nucleus of the monocularly paralyzed cat

Several converging lines of evidence suggest that the integration of binocular visual with binocular proprioceptive information takes place in the lateral geniculate nucleus (LGN) and it is very likely that such integration is necessary for normal binocular vision and depth perception. A naturally occurring visual anomaly, strabismic amblyopia, which results in the lack of normal stereoscopic vision and reduction of visual acuity, may be the outcome of a perturbation of these integrative mechanisms. Monocular paralysis, an experimental manipulation which, in part, serves to mimic some aspects of strabismic amblyopia, has been shown to disrupt binocular-visual/proprioceptive integrative mechanisms and so may serve as a model for some aspects of amblyopia. Monocular paralysis results in a highly reliable decrease in the encounter rate for X cells relative to Y cells in the LGN six days postoperative.;Questions about the nature of this effect of monocular paralysis which may yield clues about the etiology of strabismic amblyopia and binocular-visual/proprioceptive mechanisms and their plasticity may be answered, in part, by an analysis of the neural circuitry which supports the maintenance of the monocular paralysis effect. Therefore, it was the purpose of this study to test the hypothesis that the superior colliculus and cerebellum, which receive binocular-visual/proprioceptive information and have direct or indirect input to the LGN, are involved in the maintenance of the monocular paralysis effect. Standard extracellular recording techniques and a battery of tests were used to determine the relative encounter rates for X and Y cells in the LGN to confirm the X cell encounter rate shift subsequent to monocular paralysis and then, after the lesion, again to determine if the X cell encounter rate remained the same or had been restored to higher levels by the lesion. Electrolytic lesions of the colliculus in areas retinotopically matched to the LGN recording penetrations had no effect on the relative encounter rates for X and Y cells while lesions of the cerebellum increased the encounter rates for X cells in each of four cats tested. An analysis of the cerebellar lesion cites revealed that this increase in the encounter rate for X cells relative to Y cells was not a result of accidental intrusion of the lesion into the brainstem and control experiments showed it could not be attributed to surgical trauma or residual surgical anesthesia. It was suggested that the cerebellum is involved in the integration of binocular-visual/proprioceptive information and may be the source of X cell suppression which during development may result in strabismic amblyopia.