CLINICAL HANDBOOK OF SCHIZOPHRENIA

10. Cognitive Functioning in Schizophrenia 95More recent evidence for the neurodevelopmental nature of schizophrenia comesfrom an array of converging lines of evidence. A large literature suggests that certainforms of maternal influenza and/or malnutrition during key stages of pregnancy are associatedwith statistical increases in the risk of schizophrenia. Cannon, Jones, and Murray(2002) conducted a meta-analysis and found that complications during gestation (e.g.,maternal bleeding or diabetes), abnormal prenatal growth and development (e.g., lowbirthweight, reduced head circumference), and complications during birth (e.g., asphyxia,emergency caesarean section delivery) were each significantly associated with psychosis inlater life. There is also evidence of early abnormalities in motor development or functioningamong at least some of those who later develop schizophrenia. In addition, patientswith schizophrenia are more likely than the general population (and patients with someother forms of serious mental illness) to show an increased number of minor facial anomalies(which are thought to be correlated with neurodevelopmental aberrations duringgestation). Also, those at genetic risk for schizophrenia (first- and second-degree relatives),show a higher risk of subtle deficits (which consistently remain stable over time)relative to the general population.Given a neurodevelopmental model (i.e., with the possibility of abnormal neurodevelopmentpresent even during gestation), why does schizophrenia typically manifest laterin life (most typically, albeit not always, in adolescence or early adulthood)? A possibleanswer to this puzzle comes from a theory proposed by Feinberg (1982). Based on theempirical finding that an extensive reorganization of connections between cortical structures(synaptic “pruning”) occurs during adolescence, Feinberg proposed that the onsetof schizophrenia symptoms may be associated with deficits in this “pruning” process. Althoughthis idea was viewed as somewhat speculative at the time, an increasing body ofempirical research supports the notion of excessive “pruning” of certain cortical structures(particularly, the prefrontal cortex), and “underpruning” or complete failure of“pruning” of certain subcortical structures (e.g., the lenticular nuclei) among patientswith schizophrenia. In this regard, many neuroscientists now view schizophrenia as a“disconnection” syndrome; that is, at least some aspects of schizophrenia may be characterizednot only by abnormalities within specific brain regions but also in terms of disruptionsin communication/interaction between different brain areas. This notion meldsnicely with that of “adolescent pruning,” in which the interconnections are “pruned” topermit more efficient communication/interaction.Perionset Cognitive FunctioningIn addition to any subtle premorbid neurocognitive deficits, there is also evidence that furtherdecline in cognitive functioning (at a level equivalent to about 5–10 IQ points or onethirdto two-thirds of a standard deviation) generally occurs during the perionset period.Bilder and colleagues (2006) demonstrated that objective tests scores obtained from academicrecords (achievement test scores, and Scholastic Aptitude Test scores) of childrenwho developed schizophrenia in adolescence or adulthood were significantly lower thanthose of their healthy peers. Furthermore, they also demonstrated that the change in cognitiveability at first onset of schizophrenia approximated about 11.5 IQ-equivalent points.Long-Term Course of Cognitive FunctioningAs may be implied by his use of the term dementia praecox, Kraepelin’s original view ofschizophrenia was that the typical course was one of progressive decline in functioning.Although there were dissenters, this rather bleak prognostic view greatly influenced