Some call it the hardest test in the world. While "[i]ts rigors have been likened to those required to earn a degree in law or medicine", the majority of people that take this test never pursued higher education. Take Matt McCabe. Matt was a builder working alongside his father. But for the last three years Matt dedicated day after day to logging hours of study. He made 40,000 flashcards. He hung maps all over his house. He logged more than 50,000 miles on his bike. Why? Matt wanted to be a London cabbie. But to earn his seat behind the wheel of one of London's famous boxy black taxis Matt had to pass The Knowledge. Matt not only passed what some call the hardest test in the world, he also grew his brain. For the last 15 years, neuroscientist Eleanor Maguire has studied the brains of cabbies and Knowledge boys like Matt and she's discovered that the posterior hippocampus - the area of the brain known to be important for memory - of successful Knowledge candidates enlarge as the study progresses. The NYT's Jody Rosen questions whether Uber and GPS will stop this growth and make The Knowledge a test of the past.