Over the past two centuries, modern science has charted vast quantities of our solar system and constructed detailed models of the invisible particles that make-up the world's matter.

But when it comes to understanding the human brain, a complex machine comprising 100 billion neurons that make trillions of connections, scientists have no map to guide them.

On Tuesday, President Barack Obama announced his ''Brain Initiative'', a bold new plan - with $100 million initial funding - to conquer the human body's most mysterious frontier.

''The brain initiative will give scientists the tools they need to get a dynamic picture of the brain in action and better understand how we think, learn and remember,'' said Obama, at a White House news conference.