Abstract: Various NIRS studies have evaluated brain activity with intriguing and promising results. In this paper, results of an experiment using NIRS to evaluate brain activation induced by mental subtraction are discussed. The investigation evaluates activation responses of three NIR parameters, oxygenated-hemoglobin (Oxy-Hb), deoxygenated-Hb (Deoxy-Hb), and total-Hb (Tot-Hb). NIRS parameters were sensitive to mental subtraction; however, they were not sensitive to subtle variations in task difficulty. An important result was that order of presentation was significant, with activity during the first task being far greater than during the second task. Such findings raise questions about how to design cognitive studies using multiple task approaches commonly applied in brain activation research. A second topic addresses in this research was how to reduce brain activity during recovery. During nontask interval, subjects either rested or counted, which was used to reduce post-task mental activity. The nontask interval before mental subtraction (interval #1) was always lower than that of the two nontask intervals that followed cognitive performance (intervals #2 and 3). Recovery after activation was incomplete, regardless of type of nontask procedure. This suggests that recovery is still an issue needing elucidation and consideration in future designs.!3
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