Mental disorders are difficult to grasp. "The psyche" is invisible and cannot be measured. There are no conclusive answers to the question of what causes mental illness.
In the early days of psychiatry in the 19th century, research focused on the brain. Experts tried to link mental disorders to physical causes. However, this approach could not explain everything. At the same time, the theory emerged that many disorders have no biological cause but are triggered by experiences or traumas.
Over time, various test procedures have been developed to access the psyche and mental disorders: through language, image interpretation, dreams, the measurement of biochemical processes or the visualisation of brain activity.