How much of our brains do we use?

In the sci-fi movie “Lucy”, Scarlett Johansson is able to access 100 percent of her brain. According to popular claim, humans only tap into about 10 percent. Dr. Murali Doraiswamy, a globally recognized expert in the fields of cognitive neuroscience and neuropsychiatry, explains why scientists say most of the brain is active all the time. Source