fMRI evidence for both generalized and specialized components of attentional control

Abstract

A central question in the study of selective attention is whether top-down attentional control mechanisms are generalized or specialized for the type of information that is to be attended. The current study examined this question using a voluntary orienting task that cued observers to attend to either one of two locations or to one of two colors. Location (spatial) and color (nonspatial) conditions were presented either randomly intermixed within the same block of trials or in separate blocks. Functional magnetic resonance imaging revealed that directing attention to a location or to a color activated a network of overlapping dorsal frontal and parietal areas, previously implicated in attentional control. The pattern of observed overlap was not affected by the intermixed versus blocked presentation of location and color conditions. Although portions of the frontal-parietal network were more active in response to location cues than to color cues, a secondary analysis also revealed that medial dorsal frontal and parietal cortex were specifically engaged in shifting visual attention regardless of the cued dimension (location or color). Together, the present results support the conclusion that attentional control is the combination of a generalized network that works in concert with subregions of the frontoparietal network that are highly specialized for directing attention based on the content of the to-be-attended information.

Figure 1

Example of a cue-plus-target trial. The cue instructed participants to attend to a location (left, right) or color (blue, yellow) and to indicate the orientation (horizontal or vertical) of the rectangle that possessed the cued feature in the upcoming stimulus display. In the actual displays viewed by the participants, the back ground was dark grey, cues were light gray, both location targets were green, one color target was blue, and the other was yellow.

Figure 2

Cue-related activity. Group-averaged data for brain regions significantly activated by color and location attention-directing cues in the blocked task (left panel) and in the mixed task (right panel), overlaid onto a brain rendered in 3D. Areas activated by only location cues are shown in red, only color cues in blue, and those areas activated by both cues are shown in green. Cue-related activations are rendered on a partially inflated reconstruction of a spatially normalized anatomical volume using Caret (Van Essen et al., 2001; http://brainmap.wustl.edu/caret) and displayed using a height threshold of P <0.005 (uncorrected) and an extent threshold of 8 contiguous voxels.

Figure 3

Dimension-specificity in attentional control. Brain areas showing dimension-specific activity in the blocked (left column) and mixed (right column) task. Brain areas that were more strongly activated when location compared to color was cued are shown in red. Brain areas that were more strongly activated when color compared to location was cued are shown in blue. Results (p<.05) from repeated measures ANOVAs with factors Dimension (location, color) and MR Frame (1.5–13 s), performed for each task separately (and only for those voxels that were activated by location OR color cues in the first place; p<.005). Abbreviations: IPS: intraparietal sulcus, IOG: inferior occipital gyrus, pSMA: pre-supplementary motor area, PreCun: precuneus, MedFG: medial frontal gyrus, L: left, and R: right.

Figure 4

Brain areas involved in cued attention shifting. Group cue-related time courses for several frontal and parietal brain areas in the mixed-task condition, showing greater cue-related activity on switch-across vs. switch-within trials (P<.005), for location and color switch-across and switch-within trials separately. When statistically comparing cue-related peak percent (%) signal change values, no area showed a significant interaction between Switch (switch-across, switch-within) and Dimension (location, color), thereby supporting the conclusion that much of this activity reflects a generic attention switching mechanism. Abbreviations: L=left, R=right, IPS=intraparietal sulcus, ACC=anterior cingulate, med Front = medial frontal.

Figure 5

Generalization and specialization within the fronto-parietal control network. Frontal and parietal brain areas that were more strongly activated on switch-across vs. switch-within trials (p<.05) AND that were more strongly activated on location vs. color trials (p<.05) in the mixed task are shown in green. Brain areas that were more strongly activated on switch-across vs. switch-within trials are shown in blue (p<.05). Brain areas that were more strongly activated on location vs. color trials in the mixed task are shown in red (p<.05). Cue-related activations are rendered on a partially inflated reconstruction of a spatially normalized anatomical volume using Caret (Van Essen et al., 2001; http://brainmap.wustl.edu/caret).