Center for the Study of Aging and Human Development, Duke University Medical Center, Durham, NC 27710, USA.
Neuroimage. 2010 Aug 15;52(2):643-57. doi: 10.1016/j.neuroimage.2010.04.249. Epub 2010 Apr 29.
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.
任务转换需要执行控制过程，而这些过程会随着年龄的增长而衰退。先前的神经影像学研究已经确定了与全局转换效应（双任务块与单任务块）相关的大脑激活与年龄相关的差异，但在局部转换效应（块内的转换试验与重复试验）期间的激活与年龄相关的差异尚未得到研究。本实验使用功能磁共振成像（fMRI）和弥散张量成像（DTI）来研究相邻试验（即局部任务转换）中的成人年龄差异任务转换。在 fMRI 扫描期间，参与者执行了提示词分类任务。从穿插的仅提示试验中，分别估计了与提示相关的转换相关处理和与目标相关的处理。与任务转换相关的激活在分布式额顶网络内有所不同，对于提示和目标相关的处理。对于年轻成年人（n=20；18-27 岁）和老年成年人（n=20；60-85 岁），任务转换的事件相关激活幅度相似，尽管在任务期间的激活持续时间显示出一些与年龄相关的下降。关键是，在提示处理期间，与转换相关的区域的功能连接对于年轻成年人来说高于老年成年人，而在目标处理期间，功能连接在年龄组之间相当。此外，与提示相关的功能连接的个体差异与目标分类反应（漂移率）效率的年龄相关变化有很大一部分共享。然而，这种与年龄相关的功能连接差异独立于与任务相关区域内的白质完整性。这些发现强调了额顶叶激活的功能连接作为执行控制中与年龄相关衰退的潜在来源。
