Semantic control activation likelihood.

Semantic memory representations are generally well maintained in aging, whereas semantic control is thought to be more affected. To explain this phenomenon, this study tested the predictions of the Compensation-Related Utilization of Neural Circuits Hypothesis (CRUNCH), focusing on task demands in aging as a possible framework. The CRUNCH effect would manifest itself in semantic tasks through a compensatory increase in neural activation in semantic control network regions but only up to a certain threshold of task demands. This study compares 39 younger (20–35 years old) with 39 older participants (60–75 years old) in a triad-based semantic judgment task performed in an fMRI scanner while manipulating task demand levels (low versus high) through semantic distance. In line with the CRUNCH predictions, differences in neurofunctional activation and behavioral performance (accuracy and response times) were expected in younger versus older participants in the low- versus high-demand conditions, which should be manifested in semantic control Regions of Interest (ROIs). Our older participants had intact behavioral performance, as proposed in the literature for semantic memory tasks (maintained accuracy and slower response times (RTs)). Age-invariant behavioral performance in the older group compared to the younger one is necessary to test the CRUNCH predictions. The older adults were also characterized by high cognitive reserve, as our neuropsychological tests showed. Our behavioral results confirmed that our task successfully manipulated task demands: error rates, RTs and perceived difficulty increased with increasing task demands in both age groups. We did not find an interaction between age group and task demand, or a statistically significant difference in activation between the low- and high-demand conditions for either RTs or accuracy. As for brain activation, we did not find the expected age group by task demand interaction, or a significant main effect of task demand. Overall, our results are compatible with some neural activation in the semantic network and the semantic control network, largely in frontotemporoparietal regions. ROI analyses demonstrated significant effects (but no interactions) of task demand in the left and right inferior frontal gyrus, the left posterior middle temporal gyrus, the posterior inferior temporal gyrus and the prefrontal gyrus. Overall, our test did not confirm the CRUNCH predictions.

衰老过程中，语义记忆表征通常得以较好保留，而语义控制则被认为受衰老影响更为显著。为解释这一现象，本研究以衰老中的任务需求为潜在分析框架，对神经环路补偿利用假说（Compensation-Related Utilization of Neural Circuits Hypothesis，简称CRUNCH）的预测进行了验证。CRUNCH效应将通过语义控制网络脑区的神经激活代偿性增强，在语义任务中体现出来，但这一效应仅在任务需求达到特定阈值时才会显现。本研究共招募39名青年被试（20~35岁）与39名老年被试（60~75岁），让其在功能磁共振成像（fMRI）扫描仪中完成基于三元组的语义判断任务，并通过语义距离操控任务需求水平（低需求与高需求）。按照CRUNCH假说的预测，在低、高需求条件下，青年与老年被试的神经功能激活模式与行为表现（准确率与反应时）应存在差异，且该差异应体现在语义控制感兴趣区（Regions of Interest，简称ROIs）中。本研究的老年被试行为表现完好，这与既往语义记忆任务相关研究的结论一致：其准确率得以保留，但反应时（response times，简称RTs）更长。要验证CRUNCH假说的预测，老年组与青年组的行为表现需无显著年龄差异。此外，神经心理学测试结果显示，本研究的老年被试均具备较高的认知储备。行为学结果证实，本研究的任务成功操控了任务需求：在两个年龄组中，错误率、反应时与主观感知难度均随任务需求提升而升高。但本研究未发现年龄组与任务需求间存在交互效应，也未发现在低、高需求条件下，被试的反应时或准确率对应的激活水平存在统计学意义上的显著差异。就大脑激活而言，本研究未观察到预期的年龄组×任务需求交互效应，也未发现任务需求存在显著的主效应。总体而言，本研究结果与语义网络及语义控制网络存在一定程度神经激活的结论相符，激活脑区主要集中在额颞顶叶区域。感兴趣区分析显示，在左侧、右侧额下回，左侧后中颞回，后颞下回以及前额回中，任务需求均存在显著主效应（但未发现交互效应）。综上，本研究未能验证CRUNCH假说的预测。