Daselaar Sander M, Iyengar Vijeth, Davis Simon W, Eklund Karl, Hayes Scott M, Cabeza Roberto E
Center for Cognitive Neuroscience, Duke University, Durham, NC 27708, USA Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, 6525 HR, Netherlands.
Center for Cognitive Neuroscience, Duke University, Durham, NC 27708, USA.
Cereb Cortex. 2015 Apr;25(4):983-90. doi: 10.1093/cercor/bht289. Epub 2013 Oct 23.
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 less-wiring-more-firing hypothesis, which provides a testable account of compensatory over-recruitment in OAs.
可靠的神经影像学研究发现，老年人通常比年轻人表现出更强的活动（过度激活），这通常被归因于补偿作用。然而，老年人过度激活的神经机制在很大程度上尚不清楚。啮齿动物电生理学研究表明，随着回路内传入纤维数量随年龄减少，剩余的纤维会表现出更高的突触场电位（布线减少，放电增加）。外推到人类的系统水平测量，我们提出并检验了这样一个假设：老年人更强的活动是为了补偿受损的白质连接性。我们使用一套神经心理学测试，测量了与前额叶皮质（PFC）相关的执行功能和与内侧颞叶（MTL）相关的记忆功能的个体差异。我们使用事件相关功能磁共振成像，比较了源记忆任务中成功与不成功试验的活动情况。最后，我们使用扩散张量成像测量了白质完整性。该研究得出了3个主要发现。首先，执行功能较低的老年人在PFC中表现出与成功相关的更强活动，而记忆功能较低的老年人在MTL中表现出与成功相关的更强活动。其次，执行功能较低的老年人在PFC中显示出白质缺陷，而记忆功能较低的老年人在MTL中显示出白质缺陷。最后，在额叶前部和MTL区域，白质下降和与成功相关的激活都紧密相邻且呈负相关。这一发现支持了“布线减少，放电增加”假说，该假说为老年人补偿性过度激活提供了一个可检验的解释。
