The Neural Correlates of the Age-Related Decrements in Selective Attention That Occur in Healthy Cognitive Aging: an FMRI Study of the Stroop Task
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There is growing evidence that cognitive changes associated with healthy aging occur much earlier than previously believed. Yet, the vast majority of healthy cognitive aging studies neglect to analyze the gradual neural and behavioural age-related changes that surreptitiously begin in mid-adulthood and continue into late-life. Attention serves as an example of one of these mid-life behavioural changes and, as such, offers an excellent opportunity for investigation into the early, behavioural changes that begin in mid-adulthood and their associated neural underpinnings. In this study, we attempted to unearth the neural correlates of these incremental changes by subjecting participants to a rapid event-related adaptation of the classic Stroop Task, concurrently with functional MRI scans. We recruited 60 cognitively normal participants from 40-90 years of age, with 12 participants within each decade group. We found that the bilateral Middle Frontal Gyrus (MFG) was the only area to exhibit unanimous, linear age-associated declines in activity amongst all participants. Anticipating major differences in neural activity between participants who exhibited large and small Stroop interference, in comparison to their age-matched peers, we divided participants into three separate groups, based on performance. Interestingly, those who performed well on the Stroop task exhibited declines only in the MFG, while participants who performed relatively poorly demonstrated age-associated declines in every single examined region of the Frontoparietal Attention Network. Furthermore, in accordance with studies of effective age-associated functional compensation, we discovered that high performers of the Stroop task solely relied on bilateral prefrontal Attentional Network regions to maintain optimal cognitive performance. In contrast, the relatively poor performance of those who exhibited larger Stroop effects was attributable to activity in areas involved in intact distraction suppression mechanisms, like the Intraparietal Sulcus (Superior and Inferior Parietal Lobules) and the Supramarginal Gyrus of the Temporoparietal Junction. Taken together, this investigation provides corroborative evidence for the high sensitivity of the Stroop task in detecting early neural age effects, novel insights into the linear changes associated with aging from mid- to late-life, and conclusive testimony of the widening interindividual variability in the functional patterns of the brain, and subsequently behaviour, in the elderly.