Sigmund Freud continues to spark discussions today with his 1900 work "The Interpretation of Dreams," even within the field of neuroscience. According to Freud, dreams express unconscious desires that are censored by a psychological mechanism so that the dreamer does not have to wake up. Thus, the dream serves as the guardian of sleep. Neuroscientific dream researcher Allan Hobson proposed his activation-synthesis theory in 1977, which explicitly counters Freud's theses. Hobson argues that dreams arise from a physiological process in the brain (mainly in the brainstem) and have no specific psychological significance. He believes that Freud's theories are incompatible with his findings and considers Freud's theory nothing more than a psychoanalytic speculation. In contrast, neuroscientist and psychoanalyst Mark Solms offers sharp criticism.