<P> She had a difficult adolescence, and it is implied, often by Sweets, that her withdrawn social tendencies are a defense mechanism . She also sometimes struggles in identifying and explaining her emotions, and takes comfort in the rationality of her anthropological discipline . Although it has been stated that Brennan was based on a person with Asperger syndrome, this has never been confirmed in the plot of the series . The creator of the series has stated that the character was never labeled as having the syndrome in order to increase the appeal of the show on network television . This influence on her character also helps to explain her extreme rationality in early seasons, as well as some of her social difficulties . Brennan is a self - proclaimed atheist and often points out what she believes to be the irrationality of religious and spiritual beliefs . This has led to more than one argument with Booth, who is a devout Roman Catholic; he becomes particularly irate when she compares less common religions, such as voodoo, to Christianity . During the Sleepy Hollow crossover episode "Dead Men Tell No Tales", Sleepy Hollow protagonist Ichabod Crane notes that Brennan is so sceptical that she would dismiss the demon Moloch--the primary antagonist in the first two seasons of Sleepy Hollow--as nothing more than a tall man with a skin condition, although this does leave him reassured that she will not realise the nature of the secret tomb they have uncovered underneath the White House . </P> <P> Brennan is a bestselling author, who has been on the New York Times Best Seller List for 18 weeks . She is trained in three types of martial arts, has hunting licenses in four states, and has a legally registered gun as well as a diving certificate . She promised to consider becoming a vegetarian after seeing how pigs were slaughtered (which was also the way her mother had been killed). However, in "The Tough Man in the Tender Chicken" (season 5, episode 6) Angela cites health reasons for Brennan's vegetarian diet . Brennan is also a trained amateur highwire performer, and speaks at least seven other languages, including Spanish, French, Latin, Chinese, Pashto Japanese, Norwegian (although she says only "skull" and avers that, as a forensic anthropologist, this is a word she knows "in just about every language"), Farsi, and German . She has also admitted to knowing a bit of Russian . She often says she does not "put much stock in psychology" and makes a point of noting that Dr. Sweets is not a real scientist as he "bases his life on the vagary of psychology and emotions". </P> <P> Brennan's personality undergoes significant changes throughout the course of the series . Her thinking becomes less rigid in later seasons, something which is observed by Dr. Gordon Wyatt, who notes that she is now able to distinguish the difference between accuracy and truth . In season 4, Booth takes her along to his interrogations and helps her learn how to set aside her scientific perspective and relate with the victim's family and suspects on a more interpersonal level . She is also able to put aside her rationality to support her friends in sometimes irrational pursuits, such as Angela's quest to raise money to save a pig from slaughter, and to comfort Booth, even using science or quoting directly from the Bible to rationalize his religious beliefs . Her sensitivity and empathy towards others are also much improved, seen quite strongly when she comforts his grandfather, and when she attends a funeral so that the victim's single mother won't be alone . She also displays more "typical" human emotions when in extreme stress . One example of this is her fear of snakes in "The Mummy in the Maze," when a girl is in the process of being scared to death in a room, the floor teeming with snakes . This goes against her empirical nature, as, when Booth tells her that the snakes aren't venomous, she states that she is aware, but still refuses to step in the room, causing Booth to carry her on his back . </P> <P> Brennan begins to feel both dissatisfaction and discomfort with her work toward the end of the fifth season . She also sees some futility in her work, stating that no matter how many killers they catch, there will always be more . To help her gain new perspective, she later decides to head up an anthropological expedition to Indonesia for a year to identify some ancient proto - human remains, after mulling it over during the episode . However, 7 months later, she and everyone else return to D.C. in order to save Cam's job, and they all decide to stay . </P>

What season does booth and brennan get together