Abstract
Background: Premorbid cognitive deficits in schizophrenia are well documented, and have been interpreted as supporting a neurodevelopmental etiological model. We investigated 3 unresolved questions about premorbid cognitive deficits: (a) What is their developmental course? (b) Do all premorbid cognitive deficits follow the same course? (c) Are premorbid cognitive deficits specific to schizophrenia or shared by other psychiatric disorders?
Methods: Participants were members of a representative 1972–1973 birth cohort of 1,037 males and females in Dunedin, New Zealand, who were followed up to age 32 with 96% retention. We compared the cognitive development of three groups of children: those who developed schizophrenia, recurrent depression, and healthy controls.
Results: Children who developed adult schizophrenia exhibited developmental deficits (i.e., static cognitive impairments that emerge early and remain stable) on tests indexing verbal and visual knowledge acquisition, reasoning and conceptualization. In addition, these children exhibited developmental lags (i.e., growth that is slower relative to healthy controls) on tests indexing processing speed, attention, visual-spatial problem-solving ability and working memory. These two premorbid cognitive patterns were not observed in children who later developed recurrent depression.
Discussion: These findings suggest that the origins of schizophrenia include two interrelated developmental processes evident from childhood to early adolescence. Future schizophrenia cases enter primary school struggling with verbal reasoning and, as they get older, they lag further and further behind their peers in working memory, attention and processing speed.