Season 3, Episode 11 - The Maternal Congruence
Aired December 14, 2009
Leonard's mother, Dr. Beverly Hofstadter, is in town over the Christmas holiday. His mother's visit is distressing for Leonard, especially after she finds out about his relationship with Penny. Sheldon, however, is pleased to spend time with Dr. Hofstadter, whose analytical mind he finds enthralling.