Engagement in a cognitive task typically involves configuration of the mental resources needed to perform the task, and switching from one task to another involves the reconfiguration of those resources. It is believed that this configuration and reconfiguration require the preFrontal Cortex (pFC) of the brain to facilitate the activation of distributed brain areas that will be involved in task execution, and defacilitate others. Although facilitation and defacilitation may occur during task execution, I consider here that they may also be initiated in advance, as preparation for task execution. This point of view comes from a large-scale, distributed, neurocognitive, complex dynamic network understanding of brain function that emphasizes processes of task preparation and expectation (or task-set) in the brain in addition to processes of perception and action. In short, it requires that a distinction be made between task configuration processes and task execution processes. This talk will present and discuss convergent lines of evidence suggesting that pFC acts as part of a large-scale complex dynamic network to exert top-down configuration of sensory and motor brain areas in relation to task-set, that this configuration depends on top-down brain processes in the beta-frequency range, and that top-down configuration may occur when the brain is at rest prior to task execution.