Attention response functions: characterizing brain areas using fMRI activation during parametric variations of attentional load.

We derived attention response functions for different cortical areas by plotting neural activity (measured by fMRI) as a function of attentional load in a visual tracking task. In many parietal and frontal cortical areas, activation increased with load over the entire range of loads tested, suggesting that these areas are directly involved in attentional processes. However, in other areas (FEF and parietal area 7), strong activation was observed even at the lowest attentional load (compared to a passive baseline using identical stimuli), but little or no additional activation was seen with increasing load. These latter areas appear to play a different role, perhaps supporting task-relevant functions that do not vary with load, such as the suppression of eye movements.