Near‐infrared spectroscopy can detect brain activity during a color–word matching Stroop task in an event‐related design

Brain activity can be monitored non‐invasively by near‐infrared spectroscopy (NIRS), which has several advantages in comparison with other imaging methods, such as flexibility, portability, low cost and biochemical specificity. Moreover, patients and children can be repetitively examined. Therefore, the objective of the study was to test the feasibility of NIRS for the event‐related approach in functional brain activation studies with cognitive paradigms. Thus, changes in the concentration of oxy‐, deoxy‐, and total hemoglobin were measured by NIRS in 14 healthy subjects while performing a color–word matching Stroop task in an event‐related design. The hemodynamic response (increase in the concentration of oxy‐/total hemoglobin and decrease in the concentration of deoxy‐hemoglobin) was stronger during incongruent compared to congruent and neutral trials of the Stroop task in the lateral prefrontal cortex bilaterally. This stronger hemodynamic response was interpreted as a stronger brain activation during incongruent trials of the Stroop task, due to interference. A new method for NIRS data evaluation that enables the analysis of the hemodynamic response to each single trial is introduced. Each hemodynamic response was characterized by the parameters gain, lag and dispersion of a Gaussian function fitted by nonlinear regression. Specific differences between the incongruent and neutral condition were found for gain and lag. Further, these parameters were correlated with the behavioral performance. In conclusion, brain activity may be studied by NIRS using cognitive stimuli in an event‐related design. Hum. Brain Mapping 17:61–71, 2002. © 2002 Wiley‐Liss, Inc.