Psychology and Centre for Cognitive Ageing and Cognitive Epidemiology, University of Edinburgh, 7 George Square, Edinburgh EH8 9JZ, UK.
Neuroimage. 2012 Jan 16;59(2):1772-82. doi: 10.1016/j.neuroimage.2011.08.071. Epub 2011 Sep 1.
Normal ageing is associated with a decline in episodic memory, and neuroimaging studies in older adults have shown reduced activity in prefrontal cortex and other regions critical for memory function in the young. However, older adults also activate additional regions, suggesting a degree of functional reorganisation that has been attributed variously to detrimental and adaptive changes. Evaluation of these competing hypotheses depends critically upon inferences about the relative location and distribution of activity that are not well supported by current univariate or multivariate analyses. Here, we employed a recently developed model-based multivariate 'decoding' approach (Friston et al., 2008) to re-analyse a rich episodic encoding dataset and examine directly how the patterns of activity change in ageing. We assessed which spatial activity patterns, within lateral prefrontal cortex, best predict successful memory formation. Bayesian model comparison showed that the older adults had more distributed and bilateral (fragmented) predictive patterns of activity in anterior inferior frontal gyrus and middle frontal gyrus. With this direct multivariate test for changes in patterns of activity, we replicate and extend earlier findings of reduced prefrontal lateralisation in ageing. These findings extend conclusions based on conventional analyses, and support the notion that ageing alters the spatial deployment of neuronal activity, to render it less spatially coherent and regionally specific. This greater distribution of activity in older adults was also linked to poorer individual memory performance, suggesting that it reflects neural ageing, rather than adaptive compensatory responses.
正常衰老与情景记忆能力下降有关，老年人群的神经影像学研究表明，与年轻人的记忆功能相关的前额叶皮层和其他区域的活动减少。然而，老年人也会激活额外的区域，这表明存在一定程度的功能重组，这种重组归因于各种有害和适应性的变化。这些相互竞争的假说的评估取决于关于相对位置和活动分布的推断，而目前的单变量或多变量分析并不能很好地支持这些推断。在这里，我们采用了一种新的基于模型的多元“解码”方法（Friston 等人，2008 年）来重新分析一个丰富的情景编码数据集，并直接研究随着年龄的增长，活动模式如何发生变化。我们评估了在外侧前额叶皮层内，哪些空间活动模式最能预测成功的记忆形成。贝叶斯模型比较表明，老年人大脑前下额回和中额回的预测活动模式分布更广，也更偏向双侧（碎片化）。通过对活动模式变化的这种直接多元测试，我们复制并扩展了先前关于衰老过程中前额叶侧化减少的发现。这些发现扩展了基于传统分析的结论，并支持了这样一种观点，即衰老改变了神经元活动的空间配置，使其在空间上不那么连贯，区域特异性也更低。老年人大脑中这种更广泛的活动分布也与个体记忆表现较差有关，这表明这反映了神经衰老，而不是适应性的代偿反应。
