Center for the Study of Human Cognition, Department of Psychology, University of Oslo, Norway.
Rev Neurosci. 2010;21(3):187-221. doi: 10.1515/revneuro.2010.21.3.187.
The structure of the brain is constantly changing from birth throughout the lifetime, meaning that normal aging, free from dementia, is associated with structural brain changes. This paper reviews recent evidence from magnetic resonance imaging (MRI) studies about age-related changes in the brain. The main conclusions are that (1) the brain shrinks in volume and the ventricular system expands in healthy aging. However, the pattern of changes is highly heterogeneous, with the largest changes seen in the frontal and temporal cortex, and in the putamen, thalamus, and accumbens. With modern approaches to analysis of MRI data, changes in cortical thickness and subcortical volume can be tracked over periods as short as one year, with annual reductions of between 0.5% and 1.0% in most brain areas. (2) The volumetric brain reductions in healthy aging are likely only to a minor extent related to neuronal loss. Rather, shrinkage of neurons, reductions of synaptic spines, and lower numbers of synapses probably account for the reductions in grey matter. In addition, the length of myelinated axons is greatly reduced, up to almost 50%. (3) Reductions in specific cognitive abilities--for instance processing speed, executive functions, and episodic memory--are seen in healthy aging. Such reductions are to a substantial degree mediated by neuroanatomical changes, meaning that between 25% and 100% of the differences between young and old participants in selected cognitive functions can be explained by group differences in structural brain characteristics.
大脑的结构从出生到整个生命周期都在不断变化，这意味着正常的衰老、没有痴呆症，与大脑的结构变化有关。本文综述了磁共振成像（MRI）研究中关于大脑与年龄相关的变化的最新证据。主要结论如下：（1）大脑在体积上缩小，脑室系统在健康的衰老中扩张。然而，变化的模式是高度异质的，最大的变化发生在前额和颞叶皮层，以及纹状体、丘脑和伏隔核。通过 MRI 数据的现代分析方法，可以在短至一年的时间内跟踪皮质厚度和皮质下体积的变化，大多数脑区的年减少率在 0.5%到 1.0%之间。（2）健康衰老时大脑体积的减少可能与神经元损失只有很小的关系。相反，神经元的收缩、突触棘的减少和突触数量的减少可能是灰质减少的原因。此外，髓鞘化轴突的长度大大缩短，最多可达近 50%。（3）在处理速度、执行功能和情景记忆等特定认知能力方面，健康的衰老会出现下降。这些减少在很大程度上是由神经解剖学变化介导的，这意味着在选定的认知功能中，年轻人和老年人之间的差异有 25%到 100%可以用结构脑特征的组间差异来解释。
