Schizophrenia — A Neurodevelopmental or a Neurodegenerative Disorder?

Since the introduction of the concept of dementia praecox by Kraepelin, there has been debate over whether or not schizophrenia is associated with progressive cognitive decline. Methodologically, longitudinal studies are mainly used to investigate this question, but it is also sometimes investigated by comparing patients with first-episode versus chronic schizophrenia. Both strategies have some advantages as well as disadvantages (see Moritz et al., 2002), and should therefore be regarded as complementary methodological tools. Inherent problems of longitudinal studies include short test-retest periods and practice effects that potentially underestimate the degree of impairment. Cross-sectional studies, on the other hand, can easily be confounded by sample differences (especially age differences) and can only indirectly estimate intra-individual neurocognitive decline.

In accordance with several longitudinal studies, our investigations suggest that patients with first-episode and chronic schizophrenia display comparable neurocognitive profiles (Moritz et al., 2001; Moritz et al., 2002). Our results favor a neurodevelopmental model of schizophrenia over a neurodegenerative view. Furthermore, our research findings (Moritz et al., 2017, 2020) indicate that neurocognitive deficits in schizophrenia are perhaps exaggerated, as important contextual factors such as poor motivation, test anxiety and distraction by symptoms during testing that may compromise performance are not fully considered in many investigations. When such factors are taken into account, the effect size of deficits is significantly reduced (Moritz et al., 2017). Moreover, according to own studies, only a subgroup of affected individuals show cognitive impairments (Moritz et al., 2017, 2020).