A genetic predisposition to schizophrenia can be set off by exclusion from the external environment.
Migration, that is, higher exposure to social adversity, has been found to substantially increase the risk of developing schizophrenia.
Cannabis use in adolescents has been linked to schizophrenia since the 1980s, and it’s ability to stimulate internal content generation could be one reason for the high rate of use among persons on the schizophrenia spectrum.

Read more about Neurofeedback for Schizophrenia.