Enucleation demonstrates ocular dominance columns in Old World macaque but not in New World squirrel monkey visual cortex.

The effect of monocular enucleation on basophilic and metabolic staining in primary (striate) visual cortex has been compared in Old and New World monkeys. Both species show a 30-40% shrinkage of neurons in the layers of dorsal lateral geniculate nucleus receiving axons from the enucleated eye. In striate cortex Old World macaque monkeys show alternating bands of increased and diminished staining in layers 3, 4 and 6, corresponding to ocular dominance columns. New World squirrel monkeys show staining patterns in all layers which are unchanged from normal cortex, suggesting that New World monkeys lack obvious ocular dominance columns.