Near infrared spectroscopy (NIRS) is a noninvasive method to measure brain function. Changes in regional blood flow associated with neuronal activities of the brain can be evaluated according to changes in the Oxy-Hb level. In this study, we investigated changes in Oxy-Hb during double-language-induced verbal shiritori discrimination tasks in schizophrenic patients on the basis of a method to measure event-related potentials in brain waves.
The subjects were 25 schizophrenic patients and 25 age- and sex-matched healthy native Japanese speakers. The measurements were performed after explaining this study in writing and obtaining consent from all subjects.
Changes in cerebral blood flow during the tasks were measured at bilateral recording points (22 on each side) using a multi-channel NIRS system. Two contrasting events were randomly presented on the front screen (each 20 times). When it was presented with "AIU," subjects were required to phonate "AIU" (baseline task). When the other word was presented, subjects were required to perform a shiritori task (activation task: to say one word that starts with the last sound of the preceding word). Averaged waveforms for the 20 trials as each task was measured and changes in Oxy-Hb from the resting state were converted to numeric values every 100 ms.
We found that the δOxy-Hb(activation minus baseline) of the schizophrenia group significantly decreased in comparison with the healthy group during the shiritori task, and in the prefrontal area in particular, the difference was more marked. These findings suggest that a double-event-related NIRS measurement using shiritori tasks is a useful psycho-physiological index reflecting the cognitive function of schizophrenic patients.