Reduced prefrontal cortex activation during divergent thinking in schizophrenia: A multi-channel NIRS study

Relationships between deficits in verbal fluency and poor social functioning have been revealed in patients with schizophrenia. In previous studies, we demonstrated that deficits in idea fluency, which is ranked as a more complex type of verbal fluency and reflects divergent thinking ability, were more closely related to social dysfunction than deficits in simple word fluency. Although functional neuroimaging studies have provided detailed data regarding prefrontal dysfunction during word fluency tasks, the regions that relate to deficits in fluency of ideas and thoughts have not yet been clarified in schizophrenia patients. The purpose of the present study was to identify the prefrontal sub-regions responsible for deficits in idea fluency using near-infrared spectroscopy (NIRS), which is more practical than other imaging methods, and to investigate the relationships between lesions and idea fluency deficits and social dysfunction in patients with schizophrenia. Eighteen outpatients with schizophrenia and 16 healthy subjects were recruited for this case-controlled study. Using 24-channel NIRS, we measured changes in hemoglobin concentration in the prefrontal cortical surface area during idea and letter fluency tests. The analyses revealed that schizophrenia patients generally exhibited a smaller increase in the concentration of oxyhemoglobin in the frontopolar region than the controls during both the tests. However, the areas in which reduced activations were demonstrated in the patients differed remarkably between the idea and letter fluency tests: reduced activations were observed in the ventral region during the former test and in the dorsal region of the frontopolar cortex during the latter test. The reduced activations in each sub-region appeared to affect the related cognitive impairment, since the patients showed significant poorer performances than the controls on both the tests. Moreover, hypoactivity during idea fluency was significantly correlated with poor social functioning as assessed using the Global Assessment of Functioning (GAF) in the patient group. The results of the present study suggest that the ventral region within the frontopolar cortex is responsible for divergent thinking, which is associated with poor social functioning in patients with schizophrenia.

Research Highlights
► Schizophrenia exhibits reduced frontopolar activation during idea fluency task.
► The areas in which hypoactivity is shown differ between word and idea fluency tasks.
► The ventral region of the frontopolar cortex is responsible for divergent thinking.
► Hypoactivity during idea fluency task is correlated with poor social functioning.