Neural mechanisms of concurrent stimulus processing in dual tasks.

Little is known about how the human brain processes multiple relevant information streams competing for behavior. The present study aimed at specifying the interaction of the lateral prefrontal cortex (lPFC) with task-relevant sensory brain regions during concurrent stimulus processing of two relevant stimuli (S1, S2) in a classical dual-task situation. In detail, we tested whether S1 processing is independent of the task relevance of S2 as has been hypothesised in cognitive theories on dual-task processing. Using functional Magnetic Resonance Imaging, we tested two neural mechanisms that might reflect effects of S2 relevance on S1 processing at different temporal overlaps. The results indicate that: (1) activity amplitudes in S1-relevant regions in the inferior temporal cortex were similarly affected by the temporal overlap between the two stimuli when S2 was relevant or irrelevant and (2) only when S2 was relevant in the dual task, significant increases in the functional coupling between S1-relevant regions and dual-task-related regions in the posterior lPFC were present at high temporal overlap. No similar effects were found for S2-relevant regions. These findings suggest that concurrent stimulus processing in dual tasks is realised by transient changes in functional coupling for stimuli with relatively higher priority (S1).