Neural correlates of dual-task performance after minimizing task-preparation.

Previous dual-task neuroimaging studies have not discriminated between brain regions involved in preparing to make more than one response from those involved in the management and execution of two tasks. To isolate the effects of dual-task processing while minimizing effects related to task-preparatory processes, we employed a blocked event-related design in which single trials and dual trials were randomly and unpredictably intermixed for one block (mixed block) and presented in isolation of one another during other blocks (pure blocks). Any differences between dual-task and single-task trials within the mixed block would be related to dual-task performance while minimizing any effects related to preparatory differences between the conditions. For this comparison, we found dual-task-related activation throughout inferior prefrontal, temporal, extrastriate, and parietal cortices and the basal ganglia. In addition, when comparing the single task within the mixed block with the single task presented in the pure block of trials, the regions involved in processes important in the mixed block yet unrelated to dual-task operations could be specified. In this comparison, we report a pattern of activation in right inferior prefrontal and superior parietal cortices. Our results argue that a variety of neural regions remain active during dual-task performance even after minimizing task-preparatory processes, but some regions implicated in dual-task performance in previous studies may have been due to task-preparation processes. Furthermore, our results suggest that dual-task operations activate the same brain areas as the single tasks, but to a greater magnitude than the single tasks. These results are discussed in relation to current conceptions of the neural correlates of dual-task performance.