In the film that shattered box office records over the weekend, Phoenix’s sinister character explains he has a condition that causes him to laugh uncontrollably.
It's called pseudobulbar affect, also known as PBA, and it's a neurological condition characterized by uncontrollable laughing and/or crying outbursts.
The documentary “Beyond Laughter and Tears: A Journey of Hope” features people who have PBA.
“This is a neurological disorder that can be very disruptive on one’s life,” psychologist Dr. Jeff Gardere told Inside Edition. “Quite often we see people who tend to isolate themselves because they can't control these emotions.”
Nearly 2 million in the U.S. have PBA.