In this episode of Hidden Brain, Shankar Vedantam and psychologist James Pennebaker explore how language patterns can reveal insights into our mental states and personality traits. Through studies on gender differences in word usage, the impact of testosterone on language, and the analysis of written diaries, they uncover how word choices, particularly function words, signify psychological conditions like depression and anxiety. The episode also highlights the predictive power of language style matching in relationships, illustrating that couples with similar linguistic styles are more likely to stay together, while changes in language before breakups can indicate rising emotional distress.