North Face ARI SHAPIRO, host: Suppose you could raise your IQ by exercising your brain like a muscle. That's the analogy researchers are using to explain a new study that finds the IQ of teenagers can rise or fall significantly during adolescence. NPR's Allison Aubrey reports. ALLISON AUBREY: If you know what the word obstreperous means, raise your hand. Obstreperous. Yup. I can't see you out there, North Face but I would bet all of you straight A types are waving your hands. You were paying attention in school.