Top-down modulation of visual feature processing: the role of the inferior frontal junction.

Distinct areas within the visual association cortex are specialized for representing specific stimulus features, such as V4 for color and V5/hMT+ for motion. Recent studies have demonstrated that areas associated with attended features exhibit enhanced cortical activity, whereas those associated with ignored features elicit reduced activity. However, the source of this attentional (or top-down) modulation remains uncertain. A network of fronto-parietal cortical regions has been proposed as the prime candidate underlying this top-down modulation. Here, we evaluate whether there are distinct or overlapping top-down network regions for attention to different stimulus features. To this end, we explored functional magnetic resonance imaging (fMRI) functional connectivity data, electroencephalographic (EEG) source localization, and phase coherence that were obtained while participants attended or ignored motion and color stimuli. Functional connectivity analysis indicated that attention to color relies strongly on prefrontal regions, whereas attention to motion recruits both prefrontal and parietal areas. Although these networks are generally topologically segregated, both color and motion processes recruit right inferior frontal junction (IFJ). However, the IFJ may be more critical for color processing, as only connectivity with V4 predicted the degree of attentional modulation. Source localization at the time range of attentional modulation of the event related potential corroborated the role of the right IFJ and indicated that feature-based, top-down modulation occurs early during processing (< 200ms post-stimulus onset). Furthermore, long-distance alpha (8-12Hz) phase coherence between the IFJ and visual cortices may serve as a mechanism underlying anticipatory, top-down modulation of color feature processing.