Suffering from a hyper-accelerated metabolism, Bart Allen was aging at a faster rate than that of any human being thus causing him to appear the physical age of twelve when he was chronologically, and mentally only two years old. To prevent him from developing mental health problems, he was raised in a virtual reality machine which created a simulated world that kept pace with his own scale of time. When it became clear that this method was not helping, his grandmother, Iris Allen, took him back in time to the present where The Flash, Wally West, tricked Bart into a race around the world. By forcing Bart into an extreme burst of speed, Wally managed to shock his hyper-metabolism back to normal. Because he had spent the majority of his childhood in a simulated world, Bart had no concept of danger and was prone to leaping before he looked. The youth proved to be more trouble than Wally could handle, and he was pawned off onto retired superhero speedster Max Mercury, who moved Bart to Manchester, Alabama. In Impulse #50, it was revealed that Batman actually named Bart “Impulse” as a warning, not a compliment.
EHT Comics 