FORT LAUDERDALE, Fla. -

A Florida teenager is relying on the insanity defense when he goes on trial next week for brutally attacking a girl outside a middle school in 2010.

The defense says 17-year-old Wayne Treacy was suffering from post-traumatic stress disorder stemming from his brother's recent suicide. Treacy could get 50 years in prison if convicted of first-degree attempted murder for kicking and stomping Josie Lou Ratley. The attack caused permanent brain injuries.

It happened after a series of rude text messages between Treacy and Ratley. In one, she told Treacy to go be with his dead brother.

Experts say insanity defenses rarely succeed because it's difficult to convince jurors a defendant couldn't distinguish between right and wrong. There's evidence Treacy carefully planned the attack.

The trial starts Monday in Fort Lauderdale.