Less Wiring, More Firing: Low-Performing Older Adults Compensate for Impaired White Matter with Greater Neural Activity
Less Wiring, More Firing: Low-Performing Older Adults Compensate for Impaired White Matter with Greater Neural Activity
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DOI：
10.1093/cercor/bht289
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发表时间：
2015-04-01
期刊：
影响因子：
3.7
通讯作者：
Cabeza, Roberto E.
中科院分区：
文献类型：
--
作者：
Daselaar, Sander M.;Iyengar, Vijeth;Cabeza, Roberto E.
可靠的神经影像学发现，老年人通常比年轻人表现出更大的活动（过度招募），这通常归因于代偿。然而，老年人（OAs）过度招募的神经机制在很大程度上是未知的。啮齿类动物的电生理学研究表明，随着年龄的增长，神经回路中传入纤维的数量减少，保留下来的纤维显示出更高的突触场电位（更少的布线，更多的放电）。外推到人类的系统级测量，我们提出并测试了oa更大的活动补偿白质连接受损的假设。使用神经心理学测试，我们测量了与前额叶皮层（PFC）相关的执行功能和与内侧颞叶（MTLs）相关的记忆功能的个体差异。使用事件相关的功能性磁共振成像，我们比较了源记忆任务中成功和不成功试验的活动。最后，我们使用扩散张量成像测量白质完整性。这项研究产生了3个主要发现。首先，低执行能力的oa在前前额叶区表现出更大的成功相关活动，而低记忆能力的oa在中颞叶区表现出更大的成功相关活动。其次，低执行的oa在PFC中表现出白质缺陷，而低记忆的oa在mtl中表现出白质缺陷。最后，在前额叶和颞叶区域，白质下降和成功相关的激活发生在近距离，并且呈负相关。这一发现支持了“连接越少-发射越多”的假说，该假说为oa的补偿性过度招聘提供了一个可测试的解释。
The reliable neuroimaging finding that older adults often show greater activity (over-recruitment) than younger adults is typically attributed to compensation. Yet, the neural mechanisms of over-recruitment in older adults (OAs) are largely unknown. Rodent electrophysiology studies have shown that as number of afferent fibers within a circuit decreases with age, the fibers that remain show higher synaptic field potentials (less wiring, more firing). Extrapolating to system-level measures in humans, we proposed and tested the hypothesis that greater activity in OAs compensates for impaired white-matter connectivity. Using a neuropsychological test battery, we measured individual differences in executive functions associated with the prefrontal cortex (PFC) and memory functions associated with the medial temporal lobes (MTLs). Using event-related functional magnetic resonance imaging, we compared activity for successful versus unsuccessful trials during a source memory task. Finally, we measured white-matter integrity using diffusion tensor imaging. The study yielded 3 main findings. First, low-executive OAs showed greater success-related activity in the PFC, whereas low-memory OAs showed greater success-related activity in the MTLs. Second, low-executive OAs displayed white-matter deficits in the PFC, whereas low-memory OAs displayed white-matter deficits in the MTLs. Finally, in both prefrontal and MTL regions, white-matter decline and success-related activations occurred in close proximity and were negatively correlated. This finding supports the lesswiring- more-firing hypothesis, which provides a testable account of compensatory over-recruitment in OAs.