Disorganisation and depression: a re-examination of how we think and speak when depressed.

Disorganised thinking in severe mental illness seriously cripples social functions. Historically, the study of disorganisation has primarily concentrated on schizophrenia, utilizing tools designed to assess formal thought disorder (FTD). This review examines the characteristics, prevalence, and possible neural correlates of FTD within the framework of depressive disorders. Our focus is on disturbances in thought, language, and communication associated with depression, alongside the relevant subjective experiences. We also discuss the challenges and opportunities in using FTD as a predictor of future illness trajectory and advocate for using the broader construct of depressive disorganisation. We review the disruption of brain networks associated with FTD, such as the salience, language, and default mode networks, within the context of depression. In conclusion, we advocate for increased focus on personal narratives, computational psychopathology, and a broader emphasis on thought dynamics to enhance the identification of disorganisation in depression. Renewed emphasis on this neglected area of psychopathology could provide insights on improving employment and social functioning for individuals affected by mood disorders.