Perseveration in schizophrenia: failure to generate a plan and relationship with the psychomotor poverty subsyndrome

Although perseveration in the Wisconsin Card Sorting Test (WCST) has been studied extensively in schizophrenia, the underlying cognitive dysfunctions are not yet clear. In schizophrenia, perseveration has been found to relate to frontal and striatal abnormalities. Therefore, both a failure to generate a plan as seen in patients with frontal abnormalities, or a failure to execute a plan as observed in Parkinson patients, who suffer primarily from striatal abnormalities, could explain perseveration in schizophrenia. The aim of the present study was to distinguish between these two cognitive dysfunctions, which are described by Frith in his routes-to-action model. The main difference between these dysfunctions is the ability to use external guidance. In the present study, 39 schizophrenic patients and 36 healthy controls were assessed with the California Verbal Learning Test (CVLT) and the WCST, in which use of external guidance can be measured, and with the Positive and Negative Syndrome Scale (PANSS) to determine the relationship with symptomatology. The results showed that half of the schizophrenic patients showed perseveration, which could be explained by a failure to generate a plan and was related to the psychomotor poverty subsyndrome. No evidence was found for a failure to execute a plan. Type of antipsychotic medication used (atypical vs. typical) proved not relevant. The results are discussed in the light of evidence for involvement of the dorsolateral prefrontal cortex in perseveration in schizophrenia.