I travel to New York often, and I love going to see Broadway musicals. When The Book of Mormon opened, I was one of the first to buy tickets. Members of the audience were laughing all the way through. At the end, the cast got a standing ovation. Suddenly, the applause changed. Rather than a thousand people clapping separately, everyone began to clap in rhythm. Clap, clap, clap, clap. The rhythmic clapping become so insistent that the actors came back onstage for an encore. The clapping communicated approval to the actors, and they responded with another song. The neurons in your brain do something similar. They fire together in rhythmic patterns, communicating with each other across the brain. These patterns are measured in cycles per second, or Hertz (Hz). Imagine an audience clapping together slowly. That’s a slow brain wave, with millions of neurons firing together slowly. Imagine an audience clapping quickly. That’s a fast brain wave, with millions of neurons firing together quickly.