The ‘extreme female brain’ (EFB) is derived from the empathising - systemising theory (E-S) which hypothesises that sex differences in cognition exist on a continuum, based on abilities in ‘empathising’ and ‘systemising’ (Baron-Cohen, 2003). The EFB profile; extreme empathising alongside deficient systemising, has received little attention in social cognitive neuroscience research, compared to the extreme male brain, which has advanced the knowledge of sex differences in the expression of autism. Currently, there is no solid evidence of a clinical pathology relating to the EFB nor a marker of cognition associated with a person’s ‘place’ on the E-S continuum. Here, an episodic memory paradigm with social and non-social conditions was given to participants along with measures of empathising and systemising. Scores on the social condition predicted where a person lies on the E-S continuum. The thesis then investigated the hypothesis that schizophrenia is expressed in the feminised profile (Badcock & Crepsi, 2006) and the presumption that empathising and systemising demonstrate a tradeoff. Elements of paranoia were associated with an empathising bias. However, a bias in systemising ability was associated with schizotypy along with a significant overlap in the expression of autistic traits and schizotypy. Therefore, schizophrenia as a whole is unlikely to be the pathology seen in the EFB, rather, the positive symptoms of schizophrenia. A trade-off between empathising and systemising was seen but only in participants over 36 years. These results have significant implications for assessment and treatment of neuropsychological disorders and provide more specific details on the potential EFB pathology. ii