The aim of this study is to develop a near-infrared spectroscopy (NIRS)-based system that recognizes pleasant and unpleasant human emotions based on cerebral blood flow (CBF) in order to understand the minds of patients whose brain function is severely impaired. The forehead region is easily accessible to NIRS measurements, whereas the role of the anterior prefrontal cortex (PFC) in the processing of emotion remains to be elucidated. METHODSInitially, using event-related NIRS we examined changes in oxygenated hemoglobin (oxyHb) as an indicator of regional CBF changes, which reflect brain activity directly related to emotions, but not to cognitive operations in the anterior frontal regions, during viewing affective pictures. The event-related potentials (ERPs), systemic blood pressure, and pulse rate were also measured simultaneously. RESULTSThe event-related analysis of changes in oxy-Hb for a 6 s-picture presentation period showed that very unpleasant emotion was accompanied by an increase in oxy-Hb in the bilateral ventrolateral PFCs, while very pleasant emotion was accompanied by a decrease in oxy-Hb in the left dorsolateral PFC. There were no significant differences in either ERPs or autonomic nervous system activities between the two emotional states. CONCLUSIONThese findings suggest the possibility of recognizing patients' emotions from CBF changes.

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Combining spatially- and time-resolved spectroscopies. we attempted to quantitatively evaluate the contribution ratio of the partial mean pathlength of cerebral tissue to the observed overall mean pathlength, in which haemoglobin concentrations were selectively changed by administration of acetazolamide. When acetazolamide was administered, the observed increases in oxygenated haemoglobin depended on the probe distance, which became progressively larger at distances of 2, 3 and 4 cm. Increases in oxygen saturation were detected at 3 and 4 cm spacing, but not at 2 cm. Assuming that the modified Lambert-Beer's law can exist in the inhomogeneous structure of the head, then, we could estimate the contribution ratio of the cerebral tissue to optical signals at the probe distances of 2, 3 and 4 cm as 33%, 55% and 69%, respectively. Using these values, we recalculated acetazolamide-induced concentration changes in oxygenated-haemoglobin in the cerebral tissue, which resulted in the same values at distances of 2, 3 and 4 cm as expected. Thus, our present method opened the door to the possibility of selectively obtaining optical signals attributed to cerebral tissue.

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