Share or compete? Load-dependent recruitment of prefrontal cortex during dual-task performance.

Dual-task performance requires flexible attention allocation to two or more streams of information. Dorsolateral prefrontal cortex (DLPFC) is considered important for executive function, and recent modeling work proposes that attention control may arise from selective activation and inhibition of different processing units within this region. Here, we used a tone discrimination task and a visual letter memory task to examine whether this type of competition could be measurable using a neuroimaging technique, the event-related optical signal, with high spatial and temporal resolution. Left and right DLPFC structures were differentially affected by task priority and load, with the left middle frontal gyrus (MFG) being preferentially recruited by the visual memory task, whereas the two tasks competed for recruitment, in a spatially segregated manner, in right MFG. The data provide support for a competition view of dual-task processing.