Lawyers for Jerry Sandusky say they will bring in an expert to testify on "histrionic personality disorder,"  arguing that the former Penn State assistant football coach's behavior is consistent with a person suffering from this disorder. Sandusky is on trial, accused of sexually abusing 10 boys.

So -- what is histrionic personality disorder?

Generally speaking, personality disorders are complicated, tough to diagnose, and tough to treat. Histrionic -- meaning overly emotional or dramatic -- personality disorder is characterized by a constant need for attention and approval from others. It's marked by a roller coaster of emotions and, sometimes, sexually inappropriate behaviors.

Edie Mannion is a therapist with the Mental Health Association of Southeastern Pennsylvania who specializes in personality disorders. "Flirtatiousness and impulsivity are often part of it, in a person's quest for constant attention," Mannion says.

But, cautions Mannion, criminal sexual behaviors are not part of this diagnosis.

Cheryl Kennedy, a psychiatrist at UMDNJ-Medical School in Newark, agrees.

"It's extremely unusual, or unheard of almost, that people with personality disorders would conduct themselves in a criminal way around sexual behavior," Kennedy said.

Sometimes, people with certain personality disorders lack empathy for others, but that is not a trait typically associated with histrionic personality disorder.

Kennedy says that histrionic personality disorder is included in the Diagnostic and Statistical Manual of Mental Disorders, but all of the personality disorders are currently under review for the upcoming new edition of the DSM.