A large number of studies have investigated working-memory performance in schizophrenia. Meta-analysis of these studies confirms that task performance is impaired in schizophrenia more than in controls (Lee & Park, 2005), and furthermore, working-memory tasks such as the N-Back have been demonstrated in fMRI investigations to heavily recruit the prefrontal cortex (Carpenter et al. 2000); working-memory performance is also highly heritable (Ando et al. 2001). N-Back task performance phenotypes satisfy the criteria for an endophenotype of schizophrenia.
