Early involvement of prefrontal cortex in visual bottom-up attention.

Visual attention is guided to stimuli either on the basis of their intrinsic saliency against their background (bottom-up factors) or through willful search of known targets (top-down factors). Posterior parietal cortex (PPC) is thought to be important for the guidance of visual bottom-up attention, whereas dorsolateral prefrontal cortex is thought to represent top-down factors. Contrary to this established view, we found that, when monkeys were tested in a task requiring detection of a salient stimulus defined purely by bottom-up factors and whose identity was unknown before the presentation of a visual display, prefrontal neurons represented the salient stimulus no later than those in the PPC. This was true even though visual response latency was shorter in parietal than in prefrontal cortex. These results suggest an early involvement of the prefrontal cortex in the bottom-up guidance of visual attention.