The Sprague effect is the phenomenon where homonymous hemianopia, caused by damage to the visual cortex, gets slightly better when the contralesional superior colliculus is destroyed. [1] [2] The effect is named for its discoverer, James Sprague, who observed this phenomenon in 1966 using a cat model. [3] Several reasons have been thought of for this happening, including mutual inhibition between the two brain hemispheres. [4] For similar reasons of inhibiting an inhibitory structure, damaging the substantia nigra, for instance by using ibotenic acid, can also cause the same improvement. [5]