Verbal fluency in schizophrenia: does cognitive performance reflect the same underlying mechanisms in patients and healthy controls?

Verbal fluency is impaired in patients with schizophrenia, but the association with other cognitive domains remains unclear. Forty-seven patients with schizophrenia (DSM-IV) and 47 controls matched by age, gender, years of education, and vocabulary (Wechsler Adult Intelligence Scale-III) were assessed in terms of sociodemographic, clinical, and cognitive variables. Healthy controls performed significantly better than patients with schizophrenia in all cognitive measures. However, the way these cognitive domains were related differed across groups. Semantic fluency (SF) and phonological fluency (PF) were predicted by working memory (WM) in patients with schizophrenia, whereas the predictor in the healthy controls was processing speed (PS). Moreover, after dividing the sample of patients according to their performance on fluency tests, we found that a worse performance on SF or PF was predicted by WM. However, for patients with a better performance on fluency, the pattern was similar to that of healthy controls. Cognition may show a different pattern of interaction in schizophrenia, with less impaired patients showing a closer pattern to healthy controls. Therefore, we suggest that, depending on the severity of cognitive deficits, performance on neuropsychological tests may not reflect the same underlying mechanisms.