During season one's climax 'Marine One', CIA analyst Carrie Mathison (Claire Danes) was given electroshock therapy in an attempt to deal with her severe bipolar disorder.
"Carrie has had, for the first time in her life, the benefit of professional help for her disease," Gansa told The Huffington Post. "She will have been in the psych ward for a while.
"She will have been in the care of a psychiatrist for six months. She will have undergone a series of these ECT therapies. [The treatment] is not just a one-off.
"So when we find her as the second season picks up, she will be in a place where she is centred and quiet and together in a way that we haven't seen her before."
Damian Lewis's character Brody, meanwhile, will be a congressman when the new season begins.
"His seat is vacated through a scandal, and he was appointed by the governor into that seat for a temporary period of time until the election," Gansa teased.
"He's not running. Well, he will be running, but he will be a sitting congressman serving in the House of Representatives when we open the season."
Revealing the on-screen time period between the seasons, Gansa added: "I can definitely tell you where the season starts - it's around half a year after the first season. We pick up the second season six months later."
Homeland returns to Showtime on September 30.
Watch Damian Lewis talking to Digital Spy about Homeland season two below: