Inability To Lie or To Repress Thoughts

by Juan Carlos
(Puerto Rico)

Photo Credit: Victoria Landon

I'm a writer and I'm working on a story about a character that can't stop himself from saying exactly what he's thinking at any given moment. My question is: is there a psychological or neurological condition that would cause such phenomena?

I researched Asperger Syndrome, but it doesn't work for me because it's congenital and not acquired.

Thanks in advance for any help.