Although the dichotomous positive–negative distinction has gained clinical and research recognition, several reports suggest that this division is incomplete. Much of the current interest in understanding the heterogeneity of schizophrenia has involved a more detailed look at the symptoms of schizophrenia. Sophisti-cated statistical techniques utilize factor analysis to reduce data to elucidate clusters of symptoms that are most likely to group together or be found independently.
An application of this approach found that there are three, rather than two, symptom dimensions that better subdivide schiz-ophrenia. Correlational relationships between symptoms reveal that positive symptoms can be divided into two distinct groups. The first includes psychotic symptoms such as hallucinations and delusions, and the second includes symptoms of disorganization, consisting of thought disorder, bizarre behavior and inappropri-ate affect. A third group is that of negative symptoms. Although these patterns of symptoms may be seen in different proportions in individuals and may change over time, they can be shown to have distinct clinical courses and may be related to independ-ent neuropsychological deficits in a given individual (Andreasen et al., 1995).
Now it is widely accepted that schizophrenia patients experience neuropsychological deficits that can be characterized by difficul-ties with attention, information processing, executive function, learning and memory, which leads to a generalized performance deficit. Typically, there is a wide variance with some aspects of performance being more impaired then others. Interestingly, a small subgroup of the patients have cognitive functioning within the normal range Most patients with schizophrenia have only modest reductions in their IQs with an average of 90 and about 0.67 standard deviation below that of the general population. In contrast, their performance is usually worse even in first epi-sode patients. Usually patients with schizophrenia underperform relative to estimates of their premorbid functioning. Cognitive impairments involving verbal learning, verbal delayed recall, working memory, vigilance and executive functioning have a sig-nificant negative impact on social and occupational functioning. Two meta-analysis of 24 and nine studies respectively suggest that treatment with novel antipsychotic agents improve cogni-tive function compared with typical antipsychotic agents (Keefe et al., 1999; Harvey, 2001).
The degree of cognitive deficit appears to be more strongly associated with severity of negative symptoms, symptoms of disorganization and adaptive dysfunction than with positive symptoms. Verbal fluency is severely impaired in patients with psychotic disorders and the use of atypical antipsychotic medica-tions results in significant improvement. Motor functions (e.g., reaction time, motor and graphomotor speed) improve with cloz-apine, olanzapine and risperidone. Olanzapine improves motor functions more than either haloperidol or risperidone. Further-more, motor functions are related to outcome, underscoring the importance of this domain. The symbol–digit and digit–symbol tests have been among the most responsive tests to atypical antipsychotic treatment. Though the novel antipsychotic agents appear to have beneficial effects on cognition, much work still remains to eliminate biases; also, effect sizes of these improve-ments are modest (Harvey and Keefe, 2001).