Purpose:Working memory, which plays an important role in higher brain function, represents the immediate memory process that allows simultaneous storage and processing of information. Presurgical identification of the central executive system in working memory is key to preserving higher brain function during brain tumor surgery. We developed a novel counting task (digit-span task) performed during fMRI for detecting the functional location of working memory, and evaluated its usefulness in brain tumor cases.
   Material and Methods:Four patients with brain tumor who were scheduled for tumor resection via awake surgery were enrolled. fMRI was performed using a 3-T MRI scanner, and the tasks included conventional language tasks (verb generation, object naming, reading, and listening) and a counting task for evaluating working memory. The counting task consisted of task A (counting backward) and task B (counting forward) , and subtraction A from B was performed. The activated areas were anatomically evaluated and compared to those activated during other tasks.
   Results:Significant activation was seen in the left dorsal prefrontal cortex (4/4 cases) , left anterior cingulate gyrus (3/4) , and the area around the intraparietal sulcus (3/4) . These areas were mostlyinconsistent with those in standard language tasks, such as verb generation or object naming, but similar areas were activated during the reading task.
   Conclusion:These results indicate the possibility of localizing the functional area in working memory, especially verbal working memory, with a counting task during fMRI. This is a simple task useful for the presurgical evaluation of patients with brain tumors.