Effects of monocular closure at different ages on deprived and undeprived cells in the primate lateral geniculate nucleus.

This study has examined the effects of monocular visual deprivation on cells in the lateral geniculate nucleus of the primate by comparing the sizes of cells in deprived and undeprived LGN laminae of experimental rhesus monkeys with those of cells in the corresponding laminae of normal animals. A number of conclusions may be drawn from this comparison: monocular visual deprivation has major effects on cells in the undeprived LGN laminae and these vary with age at closure; the initial effect of monocular closure from birth is to cause marked hypertrophy of undeprived parvocellular cells with little shrinkage of the deprived parvocellular cells, whereas late monocular closure (after 2 months of age) causes marked shrinkage of both undeprived and deprived parvocellular cells; following monocular closure at birth, the LGN abnormality continues to evolve until at least 3 months of age, with a marked parallel shrinkage affecting both deprived and undeprived parvocellular cells. The initial hypertrophy of the undeprived cells is reversed and the deprived cells become smaller than normal; cells in the monkey LGN are sensitive to visual deprivation until about 1 year of age, much later than previously thought. Visual experience, however, modifies this sensitivity so that the effects of monocular visual deprivation are both qualitatively and quantitatively different at different ages; there are important differences between the susceptibility of cells in the magnocellular and parvocellular laminae to visual deprivation; and actual shrinkage of cells to markedly below normal size occurs and the smaller size is not simply failure of growth.