Differentiation of motor and cognitive performance characteristics in chronic schizophrenic patients

Introduction: Acute schizophrenic episodes are predominantly characterized by productive-psychotic symptoms while long-term outcome is mainly defined by negative symptoms. These feature psychomotor and cognitive decline, often show a steady progression and largely determine the socio-economic impairment of a patient. This study aimed at differentiating motor and cognitive components of negative symptoms in chronic schizophrenic patients.

Materials and Methods: We included were 18 patients (age: 36±12 years) with chronic remitted paranoid-hallucinatory schizophrenia (F20.0), and a group of age-, sex- and education matched healthy controls. All patients were treated with atypical antipsychotics, were free of psychiatric comorbidity and at least six months abstinent from any illegal drugs. Patients and controls performed a test-battery, which included basic motor speed (finger tapping) and coordination (10 times alternately tapping 30cm apart) tests as well as cognitive performance tests (Trailmarking test HAWI-R number test, MWT-B). In addition we also employed a manual stimulus-response-congruency (SRC) test, in which lateralized visual stimuli were to be answered by pressing a button with the congruent and incongruent hand, respectively.

Results: Patients were equally fast in basic motor speed (p>0.76 for finger-tapping) but took significantly longer to complete the motor coordination task (p<0.02). They also showed significantly lower performance in the trailmarking test (TMT-A: p<0.02; TMT-B: p<0.002). There was only a trend towards lower crystalline intelligence (p=0.06 for the MWT-B). In the short-term memory (numbers forward) test there was no significant effect (p>0.27), but when manipulation of memory content was required (reverse number repeat) patients were significantly worse (p<0.001).

In the SRC paradigm, patients had a significantly higher error rate than controls, while there was no difference in reaction time. Additionally, they showed a higher incongruency-effect on their performance in spite of identical switch-costs and no evidence for higher responses-impulsivity as measured by the reaction-times for incorrect responses

Conclusion: The results presented in the this study argue against a undifferentiated decline of psychomotor and cognitive performance in chronic schizophrenic patients corresponding to a global „negative syndrome“. Rather, they showed poor performance in those tasks which required handling more than one component at a time. A possible pathophysiological explanation for these findings may be found in the disconnection hypothesis which postulates a central disintegration disorder as the main underlying pathophysiology in schizophrenia.