The Clean Teen Machine

Back in Phoenix, the brothers Jonas — Nick, 15, Joe, 18, and Kevin, 20 — are preparing to start their show. All three boys stand less than five-feet-ten, and each possesses a fantastic mane of dark-brown hair. Joe's hair is ironed flat. Kevin used to flat-iron his, but now it's curly again, and he's got thick sideburns; Nick, the brothers' chief songwriter and leader, has always kept the curls. Under Nick's fitted brown linen suit is an insulin pump, adhered to his lower back. Nick was diagnosed with Type 1 diabetes in 2005 and must carefully monitor his blood-sugar levels; the band's mammoth bodyguard, Big Rob, carries an insulin shot at all times in case of an emergency.

The backstage hallway quickly fills with members of the extended Jonas family. There's the backup band — guys in their 20s, some of whom have been with the JBs since the days when they rattled around New Jersey playing grimy clubs. There's a swarm of female string players in tuxedo shirts hired to play onstage. There's the band's clean-cut co-manager, Phil McIntyre, and there's Kevin Jonas Sr., the boys' brown-haired, soft-spoken 43-year-old father. A former Christian musician and church pastor raised in North Carolina, Kevin Sr. serves with McIntyre as the band's co-manager.

The group forms a circle and clasps hands. "Two quick things," Kevin Sr. says. "We brought four people from the grass all the way to the front row tonight, so they're pretty excited." This is a Jonas norm — plucking die-hards from the nosebleeds and giving them the best seats in the house. Kevin Sr. tells the band to look out for a girl's softball team that just had a 13-year-old teammate killed in an ATV accident. "They're right at the end of the catwalk," he says. "One of them is wearing the shirt the girl was going to wear tonight."

Kevin Sr. dips his head in prayer. "Heavenly father, we just pray that you'll bless us this time, let it be fun and safe and exciting," he says. "Thank you for all the people that are here. We were at 60 percent just a week ago, and it looks full. Lord, we just pray that every person will be encouraged in Jesus' name."

The band members and crew holler. "Bring it in!" they shout. Hands are joined and raised to the ceiling.

"Livin' the dream!" they yell.

Big Rob escorts Nick, Kevin and Joe to their places. Suddenly, the lights go dark, triggering a roar in the 20,000-seat Cricket Wireless Pavilion that can only be described as primal. And it is, in a way. The neuropsychiatrist Dr. Louann Brizendine, author of the bestseller The Female Brain, says the release of dopamine in a screaming teenage girl's brain upon seeing her pop idols is like "injecting heroin." Being with other screaming girls, she says, only makes the effect wilder.

"There's a thing in biology we call synchrony," Brizendine says. "Basically, one girl affects another affects another, and it becomes a domino effect building up to that level of hysteria. They are getting all these brain hits of dopamine, and also oxytocin, which is a love-and-bonding hormone. Teenage girls have so much estrogen, which just catapults the level of dopamine and oxytocin in the brain, creating this sort of ecstatic rush in themselves and others. It truly is a state of ecstatic love."

Tonight in Phoenix, as the Jonas Brothers kick off with their buoyant, guitar-driven anthem, "That's Just the Way We Roll," it sounds a lot like ecstatic love. It sounds like clean, wholesome fun. It also sounds like money.