Department of Psychology, University of Michigan, East Hall, Ann Arbor, MI, USA.
Cortex. 2010 Apr;46(4):462-73. doi: 10.1016/j.cortex.2009.11.009. Epub 2009 Dec 22.
Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies have revealed age-related under-activation, where older adults show less regional brain activation compared to younger adults, as well as age-related over-activation, where older adults show greater activation compared to younger adults. These differences have been found across multiple task domains, including verbal working memory (WM). Curiously, both under-activation and over-activation of dorsolateral prefrontal cortex (DLPFC) have been found for older adults in verbal WM tasks. Here, we use event-related fMRI to test the hypothesis that age-related differences in activation depend on memory load (the number of items that must be maintained). Our predictions about the recruitment of prefrontal executive processes are based on the Compensation-Related Utilization of Neural Circuits Hypothesis (CRUNCH; Reuter-Lorenz and Cappell, 2008). According to this hypothesis, more neural resources are engaged by older brains to accomplish computational goals completed with fewer resources by younger brains. Therefore, seniors are more likely than young adults to show over-activations at lower memory loads, and under-activations at higher memory loads. Consistent with these predictions, in right DLPFC, we observed age-related over-activation with lower memory loads despite equivalent performance accuracy across age groups. In contrast, with the highest memory load, older adults were significantly less accurate and showed less DLPFC activation compared to their younger counterparts. These results are considered in relation to previous reports of activation-performance relations using similar tasks, and are found to support the viability of CRUNCH as an account of age-related compensation and its potential costs.
正电子发射断层扫描（PET）和功能磁共振成像（fMRI）研究揭示了与年龄相关的激活不足，即与年轻人相比，老年人的大脑区域激活程度较低，以及与年龄相关的过度激活，即与年轻人相比，老年人的大脑激活程度更高。这些差异在多个任务领域都有发现，包括言语工作记忆（WM）。奇怪的是，在言语 WM 任务中，老年人的背外侧前额叶皮层（DLPFC）也出现了激活不足和过度激活。在这里，我们使用事件相关 fMRI 来检验这样一个假设，即激活的年龄差异取决于记忆负荷（必须保持的项目数量）。我们关于前额叶执行过程招募的预测是基于补偿相关利用神经回路假说（CRUNCH；Reuter-Lorenz 和 Cappell，2008）。根据这一假说，老年人的大脑需要更多的神经资源来完成计算目标，而年轻人的大脑则需要更少的资源。因此，老年人在较低的记忆负荷下更有可能表现出过度激活，而在较高的记忆负荷下则表现出激活不足。与这些预测一致，在右侧 DLPFC，我们观察到较低的记忆负荷与年龄相关的过度激活，尽管在年龄组之间的表现准确性相当。相比之下，在最高的记忆负荷下，与年轻成年人相比，老年人的准确性显著降低，并且 DLPFC 的激活程度也较低。这些结果与使用类似任务的激活-表现关系的先前报告一起被考虑，并被发现支持 CRUNCH 作为与年龄相关的补偿及其潜在成本的解释的可行性。
