Edridge-Green Lecture. Competition and cooperation in visual development.

Studies of the effect of visual deprivation on cells in the lateral geniculate nucleus (LGN) show that there are two distinct sensitive periods in the monkey during which different reactions between the visual pathways related to the two eyes predominate and requirements for recovery from deprivation differ. The first extends from birth to about 8 weeks of age. The main interaction between the pathways from the two eyes is competitive, segregation of cortical ocular dominance columns occurs during this early period and monocular deprivation results initially in hypertrophy of undeprived LGN cells, with later parallel shrinkage of both deprived and undeprived parvocellular cells. Simply reopening the closed eye produces no recovery but reverse suture is effective in reversing some of the changes. The second sensitive period starts from about 8 weeks of age, although the peak of the later sensitivity appears to be at 7-9 months of age and some effect is still present at 12-18 months. During this later phase a cooperative interaction between the pathways related to the two eyes is necessary for normal development and in the absence of this selective shrinkage of both deprived and undeprived parvocellular LGN cells occurs. Simply reopening an eye during this late sensitive period allows recovery of these cells to normal size.