The neural basis of task-switching in working memory: Effects of performance and aging

We studied the performance of young and senior subjects on a well known wor king memory task, the Operation Span. This is a dual-task in which subjects perform a memory task while simultaneously verifying simple equations. Pos itron-emission tomography scans were taken during performance. Both young a nd senior subjects demonstrated a cost in accuracy and latency in the Opera tion Span compared with performing each component task alone (math verifica tion or memory only). Senior subjects were disproportionately impaired rela tive to young subjects on the dual-task. When brain activation was examined for senior subjects, we found regions in prefrontal cortex that were activ e in the dual-task, but not in the component tasks. Similar results were ob tained for young subjects who performed relatively poorly on the dual-task; however, for young subjects who performed relatively well in the dual-task , we found no prefrontal regions that were active only in the dual-task. Re sults are discussed as they relate to the executive component of task switc hing.