Visual cortex

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. 

In 2369, tampering by solanogen-based lifeforms caused elevated levels of serotonin to concentrate in the visual cortex and hippocampus of several crewmembers of the USS Enterprise (NCC-1701-D). Doctor Beverly Crusher realized that this was caused by a neuro-sedative used by the aliens to sedate the victims they experimented on. 

The same year, Doctor Julian Bashir performed a neural imaging scan to stimulate Chief O'Brien's visual cortex. 

Soon after, Ty Kajada asked Bashir to run a retinal imaging scan on Rao Vantika's corpse to confirm there was no residual activity in the Kobliad's visual cortex.