The visual cortex was a part of the cerebral cortex, which was a part of the brain. When Romulans brainwashed Geordi La Forge in 2367, they connected him to a device that could send images directly to his visual cortex, thereby making it impossible for La Forge to look away. (TNG: "The Mind's Eye" ) The same year, Doctor Julian Bashir performed a neural imaging scan to stimulate Chief O'Brien's visual cortex. (DS9: "Babel")