[Differentiation of deficit and non-deficit schizophrenia based on cognitive functions]

Cognitive dysfunction is a core feature in schizophrenia and has a great impact on psychosocial functioning. Still it remains unclear, whether the different diagnostic subgroups have a specific cognitive profile. The topic of this research was to investigate the neurocognitive characteristics of deficit and non-deficit schizophrenia, and to examine if the two diagnostic subgroups have a qualitative difference in cognitive functioning. In Study 1., 275 patient and 130 healthy controls completed the WCST (Wisconsin Card Sorting Test). We performed an exploratory factor analytic study on the variables for the total group and each subgroups, then we assessed the ability of the factors to distinguish between the deficit, non deficit and control groups. In Study 2., I used the Kilroy-test to investigate procedural and context-dependent learning. 78 patients and 30 healthy controls completed the test, which has two phases: while the training phase is dominantly related to basal ganglia circuits, the context-dependent probe phase requires intact medial-temporal lobe functioning. Thus the two interactive memory systems can be examined separately within one test. Study 1.: Results of the exploratory factor analysis of the whole sample yielded two factors which together explained approximately 95% of the total variance. Comparison of the diagnostic groups on each of the factors revealed that both schizophrenia groups showed executive function impairment in comparison to controls. Deficit patients suffer from a more severe degree of impairment on the "General executive function" factor (conceptualization, flexibility, set shifting) than non-deficit patients. On the other hand, non-perseverative error type (factor 2.) seems to be less typical to deficit than to the non-deficit patients. Study 2.: Results revealed that deficit and non-deficit patients were similarly impaired on the probe phase compared with controls. However, the training phase was not compromised in non-deficit patients, but deficit patients showed a significant impairment. While context-dependent learning is uniformly impaired in schizophrenia, procedural learning remains relatively intact in non-deficit patients. In conclusion, the two diagnostic subgroups seem to differ not only in the degree of cognitive impairment, but in the characteristics as well. The deficit-syndrome can be characterized by a specific profile regarding executive function, and shows greater impairment in procedural learning.