Abstract
Background: There is compelling evidence that individuals with schizophrenia exhibit impairment on a wide range of neuropsychological tasks notably those involving attention, language and memory. However, it is not known whether such deficits predate the diagnosis.
Methods: The Dunedin Multidisciplinary Health and Development Study is an unselected prospective birth cohort of 1037 individuals born in Dunedin, New Zealand between April 1, 1972 and March 31, 1973. Study members have participated in ten assessments between ages 3 and 26 including a neuropsychological test battery at age 13. Of the 850 cohort members who participated in the study at age 13, complete neuropsychological assessment data is available on 710 subjects.
Results: Psychiatric diagnostic interviews conducted at age 26 revealed that 21 of these individuals fulfilled diagnostic criteria for schizophreniform disorder, 10 for mania and 198 for depressive disorder or anxiety disorder. Study members with a subsequent diagnosis of schizophreniform disorder performed significantly worse than the other groups at age 13 on the Trails B test (time to completion), the Grooved Pegboard test (both left and right hands), and the Rey Auditory Verbal Learning Test (delayed recall and recognition). No significant differences were noted between the groups on the Rey Osterreith Copy score, the Wisconsin Card Sort Test or on Verbal Fluency.
Conclusion: These results indicate that deficits in executive functioning, verbal memory, learning and psychomotor speed are evident before the onset of schizophrenia in a representative birth cohort.