Distinct patterns of blood oxygenation in the prefrontal cortex in clinical phenotypes of schizophrenia and bipolar disorder

Background: Schizophrenia (SZ) and bipolar disorder (BD) are characterized by different clinical symptoms, and have previously been considered as categorically separate. However, several lines of evidence controversially suggest that these two disorders may run on a continuum. While it is therefore important to evaluate the subtle differences between SZ and BD, few studies have investigated the difference of brain functioning between the two by focusing on the common symptoms of cognitive functioning and impulsivity, rather than positive/negative and mood symptoms. Recent developments in near-infrared spectroscopy (NIRS) technology have enabled noninvasive assessment of brain function in people with psychiatric disorders. Methods: Near-infrared spectroscopy (NIRS) using 24-channels was conducted during the verbal fluency task (VFT) and Stroop color-word task (SCWT) in 38 patients diagnosed with SZ, 34 patients with BD, and 26 age- and sex-matched healthy controls. Results: Oxyhemoglobin changes in the prefrontal cortex (PFC) were significantly lower particularly in the SZ compared to control group during the VFT. On the other hand, these were significantly lower particularly in the BD and SZ group to control group during the SCWT. Regression analysis showed that hemodynamic changes were significantly correlated with verbal memory and impulsivity in both disorders. Conclusion: These findings suggest that different hemodynamic responses in the prefrontal cortex might reflect cognitive functioning and impulsivity, providing a greater insight into SZ and BD pathophysiology.