In the late 1920s, Lacan singled out his concept of "mental automatism". This brought together many seemingly disparate phnomena of madness under the common motif of something being imposed from 'outside'.: the echo of thoughts or a commentary on one's actions, for example.
The form of a particular psychosis would then be determined by how one made sense of these elements which lacked an initial content. Lacan would say that this concept was the closest that contemporary French psychiatry got to a structural analysis, with its emphasis on the imposition of formal elements beyond the "conscious" control of the subject.