TED is dedicated to ideas worth spreading. And that leaves many wondering exactly which ideas have been spread the most widely in the six years that TEDTalks videos have been available online. Here, a list of the 20 most-watched talks on all the platforms we track: TED.com, YouTube, iTunes, embed and download, Hulu and more.

From education to brain function to inspiring messages to techno-possibilities, this list represents quite a breadth of topics.