Cortical activation during two verbal fluency tasks in schizophrenic patients and healthy controls as assessed by multi-channel near-infrared spectroscopy

Abstract 

Near-infrared spectroscopy (NIRS) is an optical imaging method that allows non-invasive in-vivo measurements of changes in the concentration of oxygenated (O₂Hb) and deoxygenated (HHb) hemoglobin in brain tissue. For the present study, we examined 12 schizophrenic patients and 12 age- and gender-matched healthy controls by means of multi-channel NIRS (Optical Topography; ETG-100, Hitachi Medical Co., Japan) during performance of two versions of the Verbal Fluency Test (VFT; letter and category version). The results indicate that the verbal fluency tasks generally led to clear frontal activation in healthy controls, which was significantly reduced in schizophrenic patients. The letter version of the VFT induced overall stronger activation than the category version, the group difference being particularly pronounced for phonological fluency. Moreover, significant positive correlations between task-related activation effects in prefrontal and temporal NIRS channels were found in both schizophrenic patients and healthy controls. The results confirm functional deficits within the frontal lobe in patients suffering from schizophrenic illnesses, but do not confirm previous findings on abnormal fronto-temporal correlations or increased temporal activation in this group of patients. The data furthermore underline the usefulness of functional NIRS in monitoring hemodynamic responses associated with cognitive processes in healthy controls and patients with neuro-psychiatric disorders.

Keywords: Near-infrared spectroscopy (NIRS), Optical topography, Verbal Fluency Test (VFT), Schizophrenia, Frontal lobe, Dorsolateral prefrontal cortex (DLPFC)