Futurama Episodes

The Earth is conquered by flying brains with the power to turn normal human beings into idiots. On a distant planet, Leela learns that humanity’s single hope is Fry — the only being immune to the brains’ moron-making power. So Leela must return and enlist Fry’s help without becoming an imbecile herself.
wikipedia.org summary:
Earth is invaded by super-intelligent flying brains, who sap the Earth’s populace of their intelligence. Leela is taken to Nibbler’s home planet Eternia, where the Nibblonians explain that only one human is immune to the brains’ powers – Fry.
imdb.com summary:
When flying brains invade, Fry is the only one who can save the Earth from destruction