Browsing by Author "Bucur, Barbara"

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    Adult age differences in functional connectivity during executive control.
    (Neuroimage, 2010-08-15) Madden, David J; Costello, Matthew C; Dennis, Nancy A; Davis, Simon W; Shepler, Anne M; Spaniol, Julia; Bucur, Barbara; Cabeza, Roberto
    Task switching requires executive control processes that undergo age-related decline. Previous neuroimaging studies have identified age-related differences in brain activation associated with global switching effects (dual-task blocks versus single-task blocks), but age-related differences in activation during local switching effects (switch trials versus repeat trials, within blocks) have not been investigated. This experiment used functional magnetic resonance imaging (fMRI), and diffusion tensor imaging (DTI), to examine adult age differences in task switching across adjacent trials (i.e., local task switching). During fMRI scanning, participants performed a cued, word categorization task. From interspersed cue-only trials, switch-related processing associated with the cue was estimated separately from the target. Activation associated with task switching, within a distributed frontoparietal network, differed for cue- and target-related processing. The magnitude of event-related activation for task switching was similar for younger adults (n=20; 18-27years) and older adults (n=20; 60-85years), although activation sustained throughout the on-tasks periods exhibited some age-related decline. Critically, the functional connectivity of switch-related regions, during cue processing, was higher for younger adults than for older adults, whereas functional connectivity during target processing was comparable across the age groups. Further, individual differences in cue-related functional connectivity shared a substantial portion of the age-related variability in the efficiency of target categorization response (drift rate). This age-related difference in functional connectivity, however, was independent of white matter integrity within task-relevant regions. These findings highlight the functional connectivity of frontoparietal activation as a potential source of age-related decline in executive control.
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    Effects of adult age and blood pressure on executive function and speed of processing.
    (Experimental aging research, 2010-04) Bucur, Barbara; Madden, David J
    Previous research has established that the effects of chronically increased blood pressure (BP) on cognition interact with adult age, but the relevant cognitive processes are not well defined. In this cross-sectional study, using a sample matched for age, years of education, and sex, 134 individuals with either normal BP (n = 71) or chronically high BP (n = 63) were categorized into younger (19-39 years), middle-aged (41-58 years), and older (60-79 years) groups. Using a between-subjects analysis of variance (ANOVA), covarying for race and years of education, composite measures of executive function and perceptual speed both exhibited age-related decline. The executive function measure, however, was associated with a differential decline in high BP older adults. This result held even when the executive function scores were covaried for speed, demonstrating an independent, age-related effect of higher BP on executive function.
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    Influence of encoding difficulty, word frequency, and phonological regularity on age differences in word naming.
    (Experimental aging research, 2011-05) Allen, Philip A; Bucur, Barbara; Grabbe, Jeremy; Work, Tammy; Madden, David J
    It is presently unclear as to why older adults take longer than younger adults to recognize visually presented words. To examine this issue in more detail, the authors conducted two word-naming studies (Experiment 1: 20 older adults and 20 younger adults; Experiment 2: 60 older adults and 60 younger adults) to determine the relative effects of orthographic encoding (case type), lexical access (word frequency), and phonological regularity (regular vs. irregular phonology). The hypothesis was that older adults attempt to compensate for sensory and motor slowing by using progressively larger perceptual units (holistic encoding). However, if forced to use smaller perceptual units (e.g., by using mixed-case presentation), it was predicted that older adults would be particularly challenged. Older adults did show larger case-mixing effects than younger adults (suggesting that older adults' performances were especially poor when they were forced to use smaller perceptual units), but there were no age differences in word frequency or phonological regularity even though both age groups showed main effects for these variables. These results suggest that lexical access skill remains stable in the addressed (orthographic/semantic) and assembled (phonological) routes over the life span, but that older adults slow down in recognizing words because it takes them longer to normalize (perceptually "clean up") noisier sensory information.