Binocular competition in the control of geniculate cell growth

Abstract It has been shown previously that, in kittens, geniculate laminae that are visually deprived by a unilateral lid‐suture grow less than normal. However, cell growth is affected only where the deprived laminae lie opposite a normally innervated lamina. The most lateral part of lamina A, which is innervated from the monocular crescent of the visual field and which extends beyond the edge of lamina A1, is not affected by lid‐suture. One interpretation of this result is that a binocular competition controls geniculate cell growth and that the normal competitive balance is upset by the lid‐suture. In order to test this interpretation further, four kittens had the lids of one eye sutured and in the other eye a patch of temporal retina was destroyed. After 5.5 to 12 weeks′ survival lamina A1 showed a patch of transneuronal degeneration produced by the ipsilateral retinal lesion. Most of lamina A showed a reduced cell growth contralateral to the suture. However, the part of this lamina lying opposite the zone of transneuronal degeneration contained cells that were larger than would be expected if there were no competitive effect. These results show that geniculate cells compete during development, probably for available synaptic surfaces upon cortical cells, perhaps in terms of interlaminar inhibitory mechanisms. Success in this competition depends upon the nature of the visual input. The present results provide no evidence that visual deprivation can change geniculate cell growth by any direct, non‐competitive effect.