Brain activation characteristics of schizophrenia and bipolar disorder-I patients during letter and category fluency tasks: An empirical study using functional near-infrared spectroscopy.

BACKGROUND

Schizophrenia (SP) and bipolar disorder type I (BD-I) are severe psychiatric disorders with partially overlapping clinical symptoms, resulting in difficult differential diagnosis in many cases. Therefore, objective markers are needed to ensure diagnostic accuracy and timely treatment. One strategy with the potential to provide disease markers for diagnosis and reveal potential pathogenic mechanisms is combined cognitive testing and neuroimaging. In the current study, we compared cortical activation patterns among SP, BD-I, and healthy control (HC) groups during verbal fluency tasks using functional near-infrared spectroscopy (fNIRS) to identify distinguishing biomarkers.

METHODS

Sixty SP patients, 42 BD-I patients, and 44 age- and sex-matched HCs were examined by 52-channel fNIRS during the letter fluency task (LFT) and category fluency task (CFT).

RESULTS

Both patient groups exhibited performance deficits in the LFT and even larger deficits in the CFT compared to HCs. Patients with SP and HCs exhibited greater prefrontal cortex activation during the CFT than the LFT. Compared to HCs, SP patients demonstrated reduced prefrontal cortex activation during both the CFT and LFT, especially in bilateral dorsolateral and ventrolateral areas. In contrast, BD-I patients showed reduced cortical activation only during the CFT, mainly in right frontal lobe and bilateral superior temporal cortex.

LIMITATIONS: Cross-section study design, small sample sizes, and uncontrolled effects of medication.

CONCLUSIONS

Patients with SP or BD-I exhibited pronounced semantic deficits and frontal-temporal dysfunction during CFT performance compared to HCs. These findings provide several potential markers for distinguishing SP from BD-I as well as clues to the underlying network-level pathology.