Tissue hemoglobin saturation under baseline and task conditions for left and right hemispheres in patients with bipolar disorder (–◇–) and normal controls (–◆–). LF, Letter fluency task; CF, category fluency task; LCT, letter cancellation test; RCPM-A, Set A of Raven’s Colored Progressive Matrices; RCPM-B, Set B of Raven’s Colored Progressive Matrices. Values are means, with standard deviations represented by vertical bars. Note that relatively large between-subject differences of tissue oxygenation index (TOI) are found in the baseline condition, which partly explained apparently large between-subjects differences in TOI increases.