Age differences in the frontoparietal cognitive control network: implications for distractibility

Abstract

Current evidence suggests that older adults have reduced suppression of, and greater implicit memory for, distracting stimuli, due to age-related declines in frontal-based control mechanisms. In this study, we used fMRI to examine age differences in the neural underpinnings of attentional control and their relationship to differences in distractibility and subsequent memory for distraction. Older and younger adults were shown a rapid stream of words or nonwords superimposed on objects and performed a 1-back task on either the letters or the objects, while ignoring the other modality. Older adults were more distracted than younger adults by the overlapping words during the 1-back task, and they subsequently showed more priming for these words on an implicit memory task. A multivariate analysis of the imaging data revealed a set of regions, including the rostral PFC and inferior parietal cortex, that younger adults activated to a greater extent than older adults during the ignore-words condition, and activity in this set of regions was negatively correlated with priming for the distracting words. Functional connectivity analyses using right and left rostral PFC seeds revealed a network of putative control regions, including bilateral parietal cortex, connected to the frontal seeds at rest. Older adults showed reduced functional connectivity within this frontoparietal network, suggesting that their greater distractibility may be due to decreased activity and coherence within a cognitive control network that normally acts to reduce interference from distraction.

Figure 1

Example of 1-back procedure. Participants attended to either the pictures (Run 1) or the letter stimuli (Run 2) and made a speeded response to immediate repetitions in the attended modality. Letter stimuli were divided into word and nonword blocks, interleaved with blocks of fixation. ISI = interstimulus interval.

Figure 2

Mean percent priming as a function of age and attention. Error bars represent standard errors of the means.

Figure 3

Mean activation in the left inferior frontal ROI by younger and older adults across conditions. Error bars represent standard errors of the mean voxel intensity responses in each condition.

Figure 4

LV1 from the task-PLS analysis contrasting modulations of activity across all conditions in younger and older adults, shown on axial slices from the MNI152 average brain. The pattern identified by LV1 in (a) shows areas with greater activity during all 4 tasks (shown in red and associated with positive brain scores) contrasting with those showing more activity during fixation (blue areas and associated with negative brain scores in both age groups. The graph in (b) shows the mean-centered mean brain scores for both groups on this LV (error bars represent the 95% confidence intervals). A bootstrap ratio threshold of 5.0 was used to form the brain image in (a).

Figure 5

LV2 from the task-PLS analysis contrasting modulations of activity across all conditions in younger and older adults, shown on axial slices from the MNI152 average brain. The pattern identified by LV2 in (a) shows areas where younger adults had more activity during the ignore words/nonwords conditions relative to older adults. The graph in (b) shows the mean-centered mean brain scores for both groups on this LV (error bars represent the 95% confidence intervals). A bootstrap ratio threshold of 3.0 was used to form the brain image in (a).

Figure 6

Negative correlation between the degree to which each participant activated the frontoparietal control network during the ignore-words condition (brain score) and the amount of priming shown for the distracting words (r = −.53, p < .05).

Figure 7

Brain regions correlated with the right and left rostral PFC seeds in older and younger adults. Orange represents the left PFC connectivity pattern; blue represents the right PFC connectivity pattern; and green represents the overlap. The graph in (b) shows the average correlation between each seed and the pattern of regions shown in (a) across the resting state scan. A bootstrap ratio threshold of 6.0 was used to form the brain image in (a). The error bars in (b) represent standard errors of the mean correlations.

Figure 8

Brain regions showing an age difference in connectivity. Brain regions in (a) correlated with the left rostral PFC seed more strongly in younger adults than in older adults. Brain regions in (b) correlated with the right rostral PFC seed more strongly in younger adults than in older adults. The graph in (c) shows the average correlation between each seed and the pattern of regions shown in (a) and (b) across the resting state scan. A bootstrap ratio threshold of 3.0 was used to form the brain image. The error bars in (c) represent standard errors of the mean correlations.