Selective tuning of the blood oxygenation level-dependent response during simple target detection dissociates human frontoparietal subregions

Abstract

Current models of working memory and focal attention converge on the idea of an adaptable global system, distributed across a network of frontal and parietal brain regions. Here, we examine how the human frontoparietal network selectively adapts to represent currently relevant information during a simple attentional task: monitoring for a target item in a series of nontargets. Across the entire frontoparietal network, there is selective response to targets, in line with a global system for coding task-relevant inputs. At the same time, there are striking dissociations in response to nontargets; whereas ventrolateral frontal cortex responds just to the target, more dorsal/anterior regions respond to all stimuli from the target category. The results show different degrees of target selectivity across different regions of the frontoparietal network.

Figure 1.

Task design. Volunteers looked for the presentation of a target item within sequences of visually displayed nontarget items. At the beginning of a sequence, the current target item appeared with the word “target.” Sequence lengths were varied from one to eight stimuli in a row, and the target could be presented at multiple, any, or none of those positions. At the end of each sequence, the question “Was the last stimulus the target?” appeared on the screen, and the volunteer was required to respond yes or no, using a button box. Target and nontarget items were taken from a pool of stimuli, consisting of pictures from each of four distinct categories: faces, buildings, abstract line figures, and abstract shapes. The stimuli monitored could therefore be categorized according to whether they were the target item, nontargets from the same category as the target item, or nontargets from one of the other three categories.

Figure 2.

Relevance-sensitive brain areas. Results from the whole-brain analysis are shown. Green indicates brain regions that are tightly tuned to the target item; red indicates regions that are more widely tuned to the category level (see Introduction for definitions). The inset graphs display average activation levels extracted for the whole-activation clusters. Inset, Targets minus same-category nontargets and same-category nontargets minus nontargets from other categories, both contrasts at p < 0.05 uncorrected and unmasked. Little overlap (yellow) is observed between the two activation patterns even at this low threshold. TL, Temporal lobe; SMA, supplementary motor area.

Figure 3.

ROI analysis. Activation levels in the frontal cortex from the ROI analysis. There is a general trend of increased response to the nontarget items moving from VLPFC, through DLPFC to FPC. L, Left; R, right.