Early development of X-cells in kitten lateral geniculate nucleus

Lateral geniculate nucleus cells of the kitten were classified as X-cells or Y-cells with a contrast reversal test and their latencies to optic chiasm shock were measured. X-cells with mature latencies were found as early as 21 days. Y-cells did not have adult latencies at 40 days. The early development of some X-cells may be due to differential rates of fiber myelination and synaptic maturation within the lateral geniculate nucleus.