心理科学进展, 2018, 26(11): 2003-2012 doi: 10.3724/SP.J.1042.2018.02003

研究前沿

前额叶在老年阶段的可塑性及相关机制

王晨茜, 陈天勇,, 韩布新

中国科学院大学心理学系, 北京 100049

Plasticity of the prefrontal cortex in old age and underlying mechanisms

WANG Chen-Xi, CHEN Tian-Yong,, HAN Bu-Xin

Department of Psychology, University of Chinese Academy of Sciences, Beijing 100049, China

通讯作者: 陈天勇 E-mail: chenty@psych.ac.cn

收稿日期: 2017-11-13   网络出版日期: 2018-11-15

基金资助: * 国家自然科学基金项目.  81671040
国家重点研发计划项目.  2017YFC1310102

Received: 2017-11-13   Online: 2018-11-15

摘要

大量研究表明, 前额叶的结构和功能更容易受年老化影响; 然而, 近年来的研究发现, 前额叶的结构和功能在老年阶段具有一定的可塑性。对老年人进行认知训练, 能够延缓前额叶皮层厚度的萎缩, 提高白质完整性, 改善神经网络的功能连接和分化, 并可能通过调节多巴胺系统的活动改变前额叶皮质和皮质下结构的功能激活模式。有氧锻炼能够改善心脑血管功能, 保护和促进神经元的存活和生长, 引起前额叶灰质、白质体积的增加及功能激活的变化。认知训练与有氧锻炼等相结合的整合性训练不仅引起前额叶及相关认知功能的改变, 而且具有更好的生态学效度, 使老年人日常认知能力和生活质量得到提高。未来研究应采用多种技术手段, 从多个层面理解老年阶段前额叶的可塑性及相关机制; 加强对与前额叶关系密切的多种认知功能可塑性神经机制的研究; 并重视与整合性训练有关的前额叶可塑性。

关键词: 前额叶 ; 执行功能 ; 老年 ; 神经可塑性

Abstract

Previous studies have shown that structure and function of the prefrontal cortex (PFC) are particularly vulnerable to aging. On the other hand, recent studies have also indicated that the structural and functional plasticity of PFC is preserved in old age. For older adults, cognitive training attenuates reduction of cortical thickness in PFC, increases white matter integrity, improves intra- and inter-network functional connectivity, and also changes functional activation through modulation of dopamine activity in PFC and subcortical structures. Aerobic exercise improves cardiovascular fitness, preserves neuronal integrity and promotes neurogenesis, which would then lead to increased volumes in prefrontal gray and white matter, and altered functional activation patterns. Multimodal intervention, which combines cognitive training and physical exercise, has demonstrated better ecological validity, enhancing everyday cognition and life quality of older adults. We suggest that future studies should adopt various techniques, in order to better understand the prefrontal neuroplasticity in old age and its related mechanisms; separately analyze the various PFC related cognitive abilities; and lay stress on the more ecological multimodal intervention.

Keywords: prefrontal cortex ; executive function ; older adults ; neural plasticity

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本文引用格式

王晨茜, 陈天勇, 韩布新. (2018). 前额叶在老年阶段的可塑性及相关机制. 心理科学进展, 26(11), 2003-2012

WANG Chen-Xi, CHEN Tian-Yong, HAN Bu-Xin. (2018). Plasticity of the prefrontal cortex in old age and underlying mechanisms. Advances in Psychological Science, 26(11), 2003-2012

人口老龄化加速发展的背景下, 老年人的认知健康显得尤为重要(Lindenberger, 2014)。相比于其他脑区, 老年阶段前额叶的衰退开始更早且程度更重, 具体表现为皮质萎缩、白质退化、功能连接损伤及功能激活模式的变化(Grady, 2012; Raz et al., 2005; West, 1996)。前额叶与执行功能关系密切, 研究者据此提出额叶/执行衰退假说, 认为老年阶段认知功能的衰退可能源自前额叶及执行功能的损伤(Luszcz, 2011; 陈天勇, 韩布新, 罗跃嘉, 李德明, 2004)。

大量实证研究表明, 前额叶及执行功能在老年阶段具有可塑性(Park & Bischof, 2013)。近年来, 研究者的关注重点由执行功能的改善转向前额叶神经系统自身的可塑性。研究者采用认知训练、有氧锻炼, 以及二者相结合的整合性训练等干预方式, 借助结构核磁共振(sMRI)、弥散张量成像(DTI)、静息态和任务态的功能核磁共振(fMRI)、脑电(EEG、ERP)、正电子发射断层扫描(PET)等技术, 探索老年阶段前额叶在皮质结构、功能连接、功能激活及神经递质等水平上的可塑性及相关机制。

1 认知训练

前额叶主要负责与工作记忆相关的执行控制过程, 协调其他脑区完成目标导向的行为(Carlén, 2017), 在情节记忆、推理能力等高级认知功能中也发挥重要作用, 并与一般流体智力关系密切(Au et al., 2015; Binder & Desai, 2011; Donoso, Collins, & Koechlin, 2014)。因此, 关注老年阶段前额叶可塑性的研究通常采用一系列执行功能(如工作记忆和抑制控制)任务进行认知训练; 此外, 一些针对其他高级认知功能的干预研究(如记忆策略训练)也发现了老年阶段前额叶的可塑性。

1.1 前额叶结构的可塑性

老化过程中大脑皮质厚度减小, 与全脑相比, 前额叶在老年阶段的萎缩更为严重(Mander et al., 2013; Raz, 2004)。采用认知训练发现老年阶段前额叶皮质厚度增加的研究非常有限。Engvig等人(2010)对老年人进行为期8周的记忆术训练, 训练后被试眶额皮质厚度增加, 且与记忆成绩的提高相关。另外一项研究采用整合性认知训练(包括执行功能、记忆、视觉空间等任务), 发现训练后老年被试执行功能改善, 且内侧前额叶皮质厚度的萎缩相对减缓(Kim et al., 2015)。然而, 关于皮质厚度与认知功能的关系, 研究者并未达成一 致结论, 在一项横断研究中, 有认知衰退风险的老年人前额叶皮质厚度反而增加(Castro-Chavira, Barrios, Pasaye, Alatorre-Cruz, & Fernandez, 2016)。目前也还很难解释皮质结构变化影响认知能力的内在机制(Brehmer, Kalpouzos, Wenger, & Lovden, 2014)。这些研究结果提示, 采用认知训练探究老年阶段前额叶的可塑性时, 应谨慎使用皮质厚度作为检验训练效果的指标。

认知训练能够提高前额叶白质完整性。白质完整性反映大脑各区域间及区域内部的结构连接状况, 研究者借助DTI技术, 计算白质各向异性(FA)和平均扩散率(MD), 作为白质完整性的指标。老年阶段, 全脑白质完整性逐渐降低, 并与执行功能等认知能力的衰退相关(Wen et al., 2011)。对老年人进行6个月的整合性认知训练(包括工作记忆、加工速度和情节记忆任务), 被试胼胝体 前部白质(连接左右半球前额叶)的完整性提高(Lövdén et al., 2010)。上纵束是连接额、顶、枕、颞四个叶的联络纤维, 与工作记忆和执行功能联系密切(Metzler-Baddeley et al., 2017)。对老年人进行8周的记忆术训练或4周的整合性认知训练(包括推理、注意、问题解决等任务), 均发现被试上纵束白质完整性的改善(X. Cao et al., 2016; Engvig et al., 2012)。连接大脑各区域的白质纤维是信息在脑区间有效传递的基础(Antonenko & Floel, 2014), 提示前额叶的可塑性不仅体现在单个脑区功能的改善, 也体现在脑区之间连接和协作的增强。

1.2 前额叶相关网络功能连接的可塑性

研究者运用静息态fMRI技术, 计算在全脑和功能网络内部的功能连接。与前额叶及执行控制过程密切相关的内部连接网络主要包括, 定位于额顶皮质的额顶网络(FPN)和中央执行网络(CEN), 指向内部心理活动的默认模式网络(DMN), 以及驱动中央执行与默认模式网络活动切换的突显网络(SN) (Goulden et al., 2014; Luo et al., 2016)。老年阶段, 上述四个网络功能连接的损伤与整体认知能力和执行功能的衰退相关(Fjell, Sneve, Grydeland, Storsve, & Walhovd, 2016; Ng, Lo, Lim, Chee, & Zhou, 2016)。

认知训练能够增强各网络的内部功能连接。研究者采用基于策略的执行功能训练——要义推理训练, 12周后发现老年被试CEN、DMN内部功能连接增强, 且与认知表现的提高相关(Chapman et al., 2015); 3个月的整合性认知训练(包括记忆、推理、问题解决等任务)后, 老年被试CEN、DMN和SN内部连接均增强(W. Cao et al., 2016); 对遗忘型轻度认知损伤(aMCI)老年人进行6周加工速度训练, 被试在工作记忆任务的表现上出现迁移效应, 且CEN和DMN功能连接相对于控制组增强(Lin et al., 2016)。

认知训练也能促进不同网络间的功能分化。老化过程中, 神经活动的半球非对称性减弱(hemispheric asymmetry reduction in older adults, HAROLD), 去分化说(dedifferentiation theory)认为以此为代表的神经活动特异性的减弱是老年阶段整体认知衰退的标志(李婷, 李春波, 2013)。前文所述W. Cao等人(2016)的研究中, 训练后被试DMN和CEN间功能连接的负相关增强; 该训练项目还发现老年人FPN活动的半球非对称性相对加强(Luo et al., 2016), 提示大脑半球间、半球内部不同网络间功能的特异性均增强。

综上, 认知训练不仅能够提高老年人各功能网络内部神经活动的同步性, 也能够加强网络间和半球间神经活动的特异性, 上述结果与白质完整性的改善相对应, 表明前额叶神经网络的结构和功能连接在老年阶段均具有可塑性。

1.3 前额叶及皮质下结构功能激活的可塑性

采用任务态fMRI研究前额叶功能激活可塑性的成果最为丰富。相对于青年人, 老年人大脑激活的特点除前文提及的半球非对称性减弱, 还包括前部升高-后部降低(posterior-anterior shift in aging, PASA), 即完成认知任务时前额叶激活增加, 而后部低级皮层(如枕叶)激活减少, 研究者使用去分化说和代偿说(compensation theory)解释以上现象, 代偿说认为老年人通过额外的神经活动补偿神经效能的降低(具体见Grady, 2012; 李婷, 李春波, 2013的综述)。

大量工作记忆训练的研究表明, 老年阶段前额叶皮质的功能激活具有一定的可塑性。对老年人进行4周的n-back训练后, 被试任务成绩提高, 前额叶激活在低至中等难度任务中减少, 而在高难度条件未出现变化(Heinzel et al., 2016); 类似的干预研究同样也发现老年被试仅在低难度(1-back)任务中内侧、背外侧前额叶, 及运动前区皮质激活减少(Heinzel, Lorenz, et al., 2014)。神经回路的补偿性利用假说(CRUNCH)认为, 在完成简单任务时, 老年人调用更多的神经资源补偿认知效能的下降, 表现为大脑激活的增加, 而困难任务中这一补偿机制失效(Grady, 2012)。因此, 训练后老年人神经效能的提高, 表现为在简单任务中大脑补偿性激活的减少。此外, 研究提示, 与难度固定的训练相比, 难度自适应的工作记忆训练效果更好, 5周的干预后自适应训练组老年被试背外侧前额叶等脑区的激活减少幅度更大(Brehmer et al., 2011)。

工作记忆训练研究还发现, 前额叶及相关认知功能的可塑性与皮质下纹状体及多巴胺系统的活动有关。Brehmer等人(2011)发现, 工作记忆训练后老年被试纹状体尾状核在任务中激活增加, 增加的幅度与训练成绩正相关。纹状体是多巴胺系统的重要结构, 多巴胺系统的活动又与工作记忆表现密切相关(彭苏浩, 汤倩, 宣宾, 2014)。采用PET分子影像技术, 研究者进一步探索了多巴胺系统的可塑性, 但目前被试仍局限于青年群体。研究表明工作记忆训练能够调节被试多巴胺系统的活动, 表现为大脑皮质和纹状体多巴胺受体结合力(binding potential)的变化(Bäckman et al., 2011; McNab et al., 2009)。至于在老年阶段工作记忆训练能否类似地调节多巴胺系统的活动, 还需要未来实证研究的支持。

采用脑电技术, 抑制控制的训练研究也发现了前额叶在老年阶段功能激活的可塑性。对老年人和老年大鼠进行12周的抑制训练, 被试认知表现显著提升的同时, 感觉皮层的电活动均减弱; 对于人类被试, 代表自上而下抑制控制的额叶theta节律能量在干扰条件下相对降低, 提示抑制干扰信息的效能提高(Mishra, de Villers-Sidani, Merzenich, & Gazzaley, 2014)。采用延迟匹配任务和ERP考察抑制控制训练中老年人的神经可塑性, 研究者发现被试在T1D2条件(1个目标, 2个干扰)的对侧延迟活动(CDA)波幅下降, 提示抑制干扰信息的效能有改善的趋势(Ji, Wang, Chen, Du, & Zhan, 2016)。

此外, 针对认知策略进行训练也能够引起前额叶皮质功能激活的改变。在一项目标导向的自我调节注意训练中, 老年人学习使用多种策略减少分心、将注意集中在与目标有关的任务中, 训练后被试运动前区及背外侧前额叶在工作记忆任务中激活增加(Adnan, 2014)。脚手架理论认为, 此类训练促使老年人更有效地使用策略, 调用认知资源完成认知任务, 即更有效地搭建“脚手架”补偿认知衰退, 表现为训练后相应脑区功能激活的增加(Park & Bischof, 2013)。

与前额叶和执行功能相关的认知训练出现迁移效应的神经基础也已有初步的研究成果。Dahlin, Neely, Larsson, Bäckman和Nyberg (2008)发现工作记忆训练是否出现迁移效应与皮质下纹状体的功能有关。对青年人和老年人进行工作记忆训练, 仅青年被试在迁移任务中表现改善。青年被试训练前后纹状体在训练任务和迁移任务中均激活, 且训练后激活增加, 而老年被试训练前纹状体在两项任务中无显著激活, 训练后激活的增加仅发生在训练任务, 而非迁移任务。研究结果提示, 纹状体是工作记忆训练迁移效应的神经基础, 老年阶段纹状体功能的退化可能是导致迁移效应缺乏的原因。研究还发现涉及抑制控制成分的训练是否出现迁移效应与额叶theta节律能量联系密切。利用“神经赛车”视频游戏对老年人进行1个月的单任务(仅驾驶或仅辨别信号, 类似于go-nogo任务)或多任务(驾驶及辨别信号)训练, 只有多任务组被试在工作记忆、注意等迁移任务中表现改善, 并伴有额叶中线区theta节律能量增强(Anguera et al., 2013)。Mishra等人(2014)对老年人进行12周的抑制控制训练, 被试额叶theta节律能量在干扰条件下相对于控制组减小, 抑制干扰信息的效能提高, 并且在工作记忆、持续性注意等迁移任务中成绩也有改善。此外, 抑制控制训练相关的神经可塑性还可能与训练对一般认知能力的远迁移效应有关。近期我们的一项研究发现, 对老年人进行8周抑制控制训练, 被试在流体智力这一远迁移任务中表现改善, 并且远迁移效应仅与抑制控制的一个子过程——删除(deletion)中表现出的近迁移效应显著相关(Ji et al., 2016)。已有研究表明, 流体智力任务得分高的被试, 在需要更多抑制控制的lure n-back任务中表现更好, 任务中外侧前额叶等脑区的功能激活在两项认知成绩的正向关系中发挥中介作用。提示这些抑制控制相关脑区的功能激活, 可能是抑制控制训练远迁移效应出现的神经基础(Gray, Chabris, & Braver, 2003)。综上所述, 训练任务与迁移任务共享的认知和神经过程, 是迁移效应出现的基础(Beatty et al., 2015), 探索认知训练后前额叶及皮质下结构神经功能的改善与迁移效应的关系, 有助于理解训练引起迁移效应的内在机制。

2 有氧锻炼

研究发现有氧锻炼能够引起老年人前额叶皮质结构的变化。大量研究表明, 进行身体锻炼多、有氧体能(指心肺系统消耗和使用氧气的能力)好的老年人执行功能更好, 前额叶灰质体积也更大(见Erickson, Leckie, & Weinstein, 2014的综述)。对老年人进行6个月的中等强度(北欧式健步走)或低强度(健身操)有氧训练, 被试背外侧前额叶灰质体积增大(Ruscheweyh et al., 2011); 类似地, 6个月的适应个体心肺功能水平的有氧训练, 也引起老年被试前额叶灰质(额下回、辅助运动皮层)和白质(前部胼胝体)体积的增大(Colcombe et al., 2006)。另一方面, 有氧锻炼也能改变前额叶皮质和皮质下结构的功能激活。为期1年的有氧训练后, 老年被试在侧抑制任务(Flanker Task)中前额叶(额中回、额下回及运动前区)激活相对减少, 皮质下结构(丘脑、纹状体)激活增加(Voelcker-Rehage, Godde, & Staudinger, 2011)。此外, 一次性的急性有氧锻炼(Acute Aerobic Exercise)也得到研究者关注, 仅10分钟中等强度的有氧锻炼就能够引起老年人工作记忆表现的提升, 并且在任务中被试前额叶激活增加, 提示锻炼后被试能够迅速地调用任务相关的认知资源(Tsujii, Komatsu, & Sakatani, 2013)。

已有研究从不同角度探索了有氧运动引起前额叶结构和功能变化的可能机制。首先, 有氧锻炼可能通过改善心脑血管功能, 发挥对于前额叶功能的支持性作用。人类大脑的重量仅占全身 的2%, 而基础代谢量却占全身的27% (Boyer & Harrington, 2018), 更大的脑血流量能够为神经系统提供充足的氧气和营养(Hötting & Roder, 2013)。然而, 脑血流量在老年阶段下降, 且在前额叶下降最多(West, 1996)。动物研究发现, 运动训练能够引起大鼠血管内皮生长因子的增加和毛细血管的生成, 从而减缓大鼠老年阶段脑血流量的下降(Viboolvorakul & Patumraj, 2014)。以人类为被试的研究也发现, 有氧锻炼能够改善中老年人心脑血管功能, 降低心脑血管疾病的危险因素(Haskell et al., 2007; Hötting et al., 2012)。基于前额叶脑血流量在老年阶段的特异性下降, 有氧锻炼很有可能通过提升脑血流量改善前额叶功能, 但这还需要未来研究提供直接证据。

此外, 有氧锻炼还能够直接作用于神经系统, 提升神经营养因子水平, 促进神经组织代谢, 从而改善前额叶相关的认知功能。N-乙酰天冬氨酸(NAA)是一种仅在神经组织中产生的代谢物, 有氧体能好的老年人NAA水平更高, 并且NAA在有氧体能与工作记忆的正向关系中起中介作用, 提示有氧运动能够促进神经组织的代谢活动, 进而改善前额叶功能(Erickson et al., 2012)。神经营养因子对神经元的生长和存活有重要意义(路露,陈美婉,罗焕敏,2010), 并与执行功能、工作记忆表现有显著的正向关系(Bellar, Glickman, Juvancic- Heltzel, & Gunstad, 2011), 主要包括脑源性神经营养因子(BDNF)、胰岛素样生长因子(IGF-1)等。急性有氧锻炼能提高老年被试BDNF水平(de Melo Coelho et al., 2014; Håkansson et al., 2017)。采用长期有氧耐力训练或整合性运动训练的研究也发现老年被试BDNF和IGF-1水平的提高, 并且BDNF水平在有氧锻炼与执行功能的正向关系中起中介作用(Sillanpää et al., 2010; Suzuki et al., 2013)。动物研究提供了身体锻炼促进神经生长的直接证据。研究发现, 有氧运动能够减缓小鼠神经生长的随龄下降, 促进小鼠神经元的增殖、存活、分化和迁移(Littlefield, Setti, Priester, & Kohman, 2015; So et al., 2017)。前额叶在老年阶段的萎缩最快(Raz, 2004), 有氧锻炼对老年人执行功能又具有特异性的促进作用(参见综述, 李旭,杜新,陈天勇,2014); 因此, 前额叶很可能更多地获益于有氧锻炼对神经系统的保护作用。不过由于目前还难以通过在体(in vivo)研究考察人类神经元层面的变化, 因此关于有氧锻炼对人类前额叶神经保护作用的探索, 还有待技术手段的进步。

综上所述, 有氧锻炼与老年阶段前额叶及相关认知功能的可塑性密切相关。一方面, 有氧锻炼能够改善心脑血管功能, 降低心脑血管疾病的危险因素, 从而支持神经系统的功能; 另一方面, 有氧锻炼也能促进神经组织代谢, 提升神经营养因子水平, 并可能直接促进神经生长。

3 整合性训练

早期的整合性训练将认知干预、有氧锻炼等相结合, 发现前额叶的结构和功能在老年阶段具有可塑性, 并且相比于成分单一的训练, 整合性训练的效果更显著。在一项干预研究中, 进行为期6周的包括记忆术、执行功能任务、太极拳和团体心理辅导的整合性训练后, 老年被试内侧前额叶与内侧颞叶之间, 以及DMN区域的功能连接增强(Li et al., 2014)。另一项研究中, 两组老年人分别接受整合性训练(包括记忆、推理、视觉空间能力训练, 手工, 及身体锻炼)和推理能力训练, 1年后整合性训练组老年被试前额叶(额极区域)皮质厚度的萎缩减缓更多(Jiang et al., 2016)。此外, 整合性训练效果的保持也更好。对三组老年人分别进行1年的认知训练、身体锻炼及二者相结合的训练, 5年后的追踪测试发现, 整合性训练组被试在包括执行功能在内的多项认知能力上均优于其他两组(Oswald, Gunzelmann, Rupprecht, & Hagen, 2006); 与此类似, 接受3个月整合性训练(包括记忆、推理、问题解决训练、手工制作、健康知识教学和身体锻炼)的老年人, 相比于仅接受推理训练的老年人, 情节记忆等认知能力的提高在1年后保持得更好(Cheng et al., 2012)。然而, 整合性训练这些优势的神经机制还需要进一步探索。

近年来, 科技的发展也使一些更为贴近老年人实际生活、更具生态学效度的整合性训练成为可能。互动式健身游戏(exergame)能够在单个任务中同时进行认知训练和身体锻炼, 已经成为整合性训练的有效手段。研究者考察互动式健身游戏对于老年人步态的影响, 发现训练后被试在执行功能任务中前额叶theta节律能量减小, 并且在双任务行走(即行走的同时完成其他认知任务)时步态改善, 提示互动式健身游戏能够提高认知加工效能, 帮助老年人在走路时更好地注意和处理路况等信息, 进而改善步态, 降低摔倒的几率(Schättin, Arner, Gennaro, & de Bruin, 2016)。同样利用互动式健身游戏, 研究者对老年人进行8周同时涉及注意、执行控制和运动协调能力的跳舞毯游戏训练, 训练后被试在加速走任务中额叶激活减少, 认知效能提高, 且激活减少的幅度与执行功能的提高正相关(Eggenberger, Wolf, Schumann, & de Bruin, 2016)。也有研究者开始关注与社会参与有关的前额叶可塑性。体验团项目(The Experience Corps Project)安排老年人在小学进行6个月的志愿服务, 为学生提供阅读指导及图书馆服务, 训练后老年人抑制控制的成绩提高, 提高程度与外侧前额叶、前扣带回任务中功能激活的增加相关, 提示社会参与、接触丰富的环境能够促进老年人更积极地调用认知资源(Carlson et al., 2009)。

综上所述, 涵盖多种成分的整合性训练能够比成分单一的干预更为有效地改善前额叶结构和功能; 另一方面, 采用新技术手段和范式的整合性训练则可以更加贴近老年人的生活。更多地采用整合性训练探索老年阶段前额叶的可塑性, 有利于促进干预项目更好地服务于老年人的实际 生活。

4 未来研究展望

4.1 采用多种技术手段, 从多个层面理解前额叶的可塑性

早期有关老年阶段前额叶老化与可塑性的研究主要采用sMRI、fMRI、EEG等技术, 揭示前额叶结构和功能的变化。近年来, 考察白质完整性的DTI技术, 关注大脑功能连接状况的静息态fMRI技术, 以及研究神经递质系统的PET分子影像技术逐渐发展成熟。例如, 采用PET技术的研究发现, 多巴胺系统的活动是工作记忆训练中前额叶可塑性更为基础的神经机制(Bäckman et al., 2011; McNab et al., 2009)。有研究者甚至更进一步, 利用行为遗传学技术, 发现与多巴胺系统活动相关的一系列基因(如参与多巴胺酶解过程的COMT基因)可能是工作记忆可塑性个体差异的行为遗传学基础(Bellander et al., 2015; Heinzel, Riemer, et al., 2014), 从而进一步加深了对前额叶可塑性相关机制的理解。

然而, 由于技术条件和施测时间的限制, 以往的干预项目在研究中往往仅采用单一的脑成像技术, 因而只能观察到一种神经指标在训练后的变化。近年来, 多模态脑成像技术发展很快, 在一些研究领域已得到成功运用, 也开始成为探索前额叶在老年阶段可塑性的有效技术手段。例如, 已经有研究将DTI与静息态fMRI技术相结合, 发现整合性认知训练后CEN区域白质完整性的提高与功能连接的增强具有一致性, 提示前额叶结构与功能的可塑性关系紧密(Chapman et al., 2015)。在未来研究中, 随着多模态脑成像等技术的广泛应用, 无论是认知训练、有氧锻炼, 还是整合性训练, 对前额叶的影响都可以从脑结构(灰质、白质)、脑功能(神经网络间的功能连接、特定脑区的功能激活), 以及递质系统等各个层面进行研究, 从而更系统深入地理解前额叶在老年阶段的可 塑性。

4.2 加强对与前额叶关系密切的多种认知功能神经可塑性的研究

前额叶在工作记忆、执行控制、情节记忆等高级认知功能, 以及一般流体智力中均发挥重要作用(Au et al., 2015; Carlén, 2017)。目前与前额叶可塑性有关的认知训练研究中, 工作记忆训练研究的成果较为丰富, 已经发现工作记忆训练能够通过调节多巴胺系统的活动, 改变纹状体和前额叶的功能激活, 进而提升青年人的工作记忆能力。然而, 在老年阶段, 多巴胺系统是否通过同样的机制影响前额叶的可塑性仍需未来研究提供支持。值得注意的是, 针对其他认知功能的干预研究还不能系统地解释训练如何作用于前额叶皮质、皮质下结构及神经递质系统。例如, 抑制控制是一项非常基础的执行功能, 很早就已被心理学研究所关注(Smith, 1992), 其神经基础主要定位于前额叶下部-丘脑底核-运动皮层回路, 并与去甲肾上腺素、多巴胺及5-羟色胺递质系统的活动有关(Bari & Robbins, 2013)。然而, 目前抑制训练的研究尚未深入到神经回路层次, 以揭示与抑制控制相关的脑结构及神经递质系统在老年阶段的可塑性。此外, 已有研究提示同一执行过程(如抑制控制)不同子过程的可塑性也存在差异性(Ji et al., 2016), 但这些差异的神经基础还有待进一步探究。未来研究可借鉴工作记忆训练中对神经可塑性的研究思路, 加强对与前额叶关系密切的多种认知功能神经可塑性的研究, 从而增进对前额叶在老年阶段多方面的可塑性及相应神经机制的认识。

目前, 关于认知训练能的远迁移效应, 特别是能否提高老年人的一般认知能力或流体智力, 还存在较大的争议。例如, Anguera等(2013)采用“神经赛车”视频游戏进行训练, 发现训练后老年被试在工作记忆和注意等任务中成绩显著提高, 但其他研究者针对该研究的样本情况(如被试脱落率过高、样本量小)和研究结果(如迁移效应仅在3/11个任务中出现、统计分析中多重比较的校正问题等)提出了质疑(Simons, 2013)。Jaeggi, Buschkuehl, Jonides和Perrig (2008)发现8~19天的dual n-back任务训练后, 被试的流体智力有显著提高, 但也受到了对于诸如没有安慰剂对照组(仅采用无接触对照组)、迁移效应的测试不规范等问题的质疑(Chooi & Thompson, 2012)。此外, 元分析结果也表明工作记忆训练并未在其他认知能力(如言语能力、抑制控制等)上表现出迁移效应(Melby-Lervåg & Hulme, 2016)。尽管争论仍在继续, 这些认知训练中关于神经可塑性的研究也非常缺乏, 很多商业化的认知训练产品(如Cogmed, BrainHQ)却已经迅速地推向市场, 宣传可以预防老年人的认知衰退, 甚至预防AD, 并声称有科学证据的支持。针对这一现状, 以美国斯坦福大学长寿中心和德国马普人类发展研究所为首的70多位心理学家, 于2014年联名签署了《来自科学界对于认知训练产业的声明》, 认为这些所谓的“研究支持”往往与产品关系不大, 并且指出这些训练能否影响老年人的日常生活还需要更多实证研究的验证(Allaire et al., 2014)。因此, 未来研究需要在规范实验设计基础上, 进一步揭示认知训练改善老年人认知功能的神经机制, 同时也为开发商业性的认知训练产品提供更可靠的科学依据。

4.3 重视与整合性训练有关的前额叶可塑性

相比于单一成分的干预, 整合性训练不仅能更为有效地减缓前额叶在老年阶段的萎缩(Jiang et al., 2016), 并且在训练的生态学效度, 即提高老年人日常认知能力和生活质量方面也具有突出的优势。首先, 整合性训练的内容更加贴近生活, 太极拳、营养饮食教学, 甚至志愿服务都已被纳入针对老年人的干预项目(Carlson et al., 2009; Li et al., 2014; Ngandu et al., 2015)。第二, 采用新技术手段(如互动式健身游戏)的整合性训练, 使在实验室更好地模拟生活中的多任务情境成为可能。最后, 整合性训练更多地使用与实际生活能力相关的指标(如对老年人步态、日常生活能力、驾驶行为等)进行评估(Ball, Edwards, Ross, & McGwin, 2010; Rebok et al., 2014; Schättin et al., 2016), 能够更好地评价干预项目对老年人日常生活能力的影响。

近年来, 已经出现了一些具有影响力的大型训练项目。例如, 芬兰预防老年认知损伤的干预研究(FINGER)发现, 2年的整合性干预后被试执行功能相对于控制组更好(Ngandu et al., 2015)。针对健康老年人的高级认知功能训练项目(ACTIVE)发现训练后的5年间, 被试日常生活能力、驾驶行为均有显著改善(Ball et al., 2010; Rebok et al., 2014)。然而, 遗憾的是, 尽管两个干预项目所关注的执行功能、日常生活能力、驾驶行为等均与前额叶有关, 但目前还没有关于神经可塑性研究结果的报告。因此, 未来研究应着重关注与整合性训练有关的神经可塑性, 理解训练中老年人前额叶结构和功能的改变, 及与认知功能和日常生活能力改善相关的神经机制。

The authors have declared that no competing interests exist.
作者已声明无竞争性利益关系。

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Cognitive neuroscience of the healthy aging human brain has thus far addressed age-related changes of local functional and structural properties of gray and white matter and their association with declining or preserved cognitive functions. In addition to these localized changes, recent neuroimaging research has attributed an important role to neural networks with a stronger focus on interacting rather than isolated brain regions. The analysis of functional connectivity encompasses task-dependent and -independent synchronous activity in the brain, and thus reflects the organization of the brain in distinct performance-relevant networks. Structural connectivity in white matter pathways, representing the integrity of anatomical connections, underlies the communication between the nodes of these functional networks. Both functional and structural connectivity within these networks have been demonstrated to change with aging, and to have different predictive values for cognitive abilities in older compared to young adults. Structural degeneration has been found in the entire cerebral white matter with greatest deterioration in frontal areas, affecting whole brain structural network efficiency. With regard to functional connectivity, both higher and lower functional coupling has been observed in the aging compared to the young brain. Here, high connectivity within the nodes of specific functional networks on the one hand, and low connectivity to regions outside this network on the other hand, were associated with preserved cognitive functions in aging in most cases. For example, in the language domain, connections between left-hemisphere language-related prefrontal, posterior temporal and parietal areas were described as beneficial, whereas connections between the left and right hemisphere were detrimental for language task performance. Of note, interactions between structural and functional network properties may change in the course of aging and differentially impact behavioral performance in older versus young adults. Finally, studies using noninvasive brain stimulation techniques like transcranial direct current stimulation (tDCS) to simultaneously modulate behavior and functional connectivity support the importance of 'selective connectivity' of aging brain networks for preserved cognitive functions. These studies demonstrate that enhancing task performance by tDCS is paralleled by increased connectivity within functional networks. In this review, we outline the network perspective on healthy brain aging and discuss recent developments in this field.

Au, J., Sheehan, E., Tsai, N., Duncan, G. J., Buschkuehl, M., & Jaeggi, S. M. ( 2015).

Improving fluid intelligence with training on working memory: A meta-analysis

Psychonomic Bulletin & Review, 22( 2), 366-377.

URL     PMID:25102926      [本文引用: 2]

Fluid intelligence (Gf) refers to the ability to reason and to solve new problems independently of previously acquired knowledge. Gf is critical for a wide variety of cognitive tasks, and it is considered one of the most important factors in learning. Moreover, Gf is closely related to professional and educational success, especially in complex and demanding environments. Although performance on tests of Gf can be improved through direct practice on the tests themselves, there is no evidence that training on any other regimen yields increased Gf in adults. Furthermore, there is a long history of research into cognitive training showing that, although performance on trained tasks can increase dramatically, transfer of this learning to other tasks remains poor. Here, we present evidence for transfer from training on a demanding working memory task to measures of Gf. This transfer results even though the trained task is entirely different from the intelligence test itself. Furthermore, we demonstrate that the extent of gain in intelligence critically depends on the amount of training: the more training, the more improvement in Gf. That is, the training effect is dosage-dependent. Thus, in contrast to many previous studies, we conclude that it is possible to improve Gf without practicing the testing tasks themselves, opening a wide range of applications.

Bäckman, L., Nyberg, L., Soveri, A., Johansson, J., Andersson, M., Dahlin, E., ... Rinne, J. O. ( 2011).

Effects of working-memory training on striatal dopamine release

Science, 333( 6043), 718.

URL     PMID:21817043      [本文引用: 2]

Abstract Updating of working memory has been associated with striato-frontal brain regions and phasic dopaminergic neurotransmission. We assessed raclopride binding to striatal dopamine (DA) D2 receptors during a letter-updating task and a control condition before and after 5 weeks of updating training. Results showed that updating affected DA activity before training and that training further increased striatal DA release during updating. These findings highlight the pivotal role of transient neural processes associated with D2 receptor activity in working memory.

Ball, K., Edwards, J. D., Ross, L. A., & McGwin, G., Jr. ( 2010).

Cognitive training decreases motor vehicle collision involvement among older drivers

Journal of the American Geriatrics Society, 58( 11), 2107-2113.

URL     PMID:3057872      [本文引用: 2]

OBJECTIVES: To test the effects of cognitive training on subsequent motor vehicle collision (MVC) involvement of older drivers.DESIGN: Randomized, controlled, multisite, single-blind clinical trial.SETTING: Community-dwelling seniors at four U.S. sites: Birmingham, Alabama; Baltimore, Maryland; Indianapolis, Indiana; and State College, Pennsylvania.PARTICIPANTS: Nine hundred eight older drivers (mean age 73.1; 18.6% African American) who were randomized to one of three cognitive interventions or a control condition.INTERVENTIONS: Up to 10 sessions of cognitive training for memory, reasoning, or speed of processing.MEASUREMENTS: State-recorded MVC involvement up to 6 years after study enrollment.RESULTS: Speed-of-processing and reasoning training resulted in lower rates of at-fault collision involvement over the subsequent approximately 6-year period than controls. After adjusting for age, sex, race, education, mental status, health, vision, depressive symptoms, and testing site, participants randomized to the speed-of-processing and reasoning interventions had an approximately 50% lower rate (per person-mile) of at-fault MVCs than the control group (rate ratio (RR)=0.57, 95% confidence interval (CI)=0.34鈥0.96 for speed of processing), and (RR=0.50, 95% CI=0.27 0.92 for reasoning). There was no significant difference observed for the memory group.CONCLUSION: Cognitive speed-of-processing and reasoning training resulted in a lower at-fault MVC rate in older drivers than in controls. Considering the importance of driving mobility, the costs of crashes, and the benefits of cognitive training, these interventions have great potential to sustain independence and quality of life of older adults. More research is needed to understand the effects of different types and quantities of training.

Bari, A., & Robbins, T.W. ( 2013).

Inhibition and impulsivity: Behavioral and neural basis of response control

Progress in Neurobiology, 108, 44-79.

URL     [本文引用: 1]

Bellander, M., Bäckman, L., Liu, T., Schjeide, B.-M. M., Bertram, L., Schmiedek, F., ... Lövdén, M. ( 2015).

Lower baseline performance but greater plasticity of working memory for carriers of the val allele of the COMT Val158Met polymorphism

Neuropsychology, 29( 2), 247-254.

URL     [本文引用: 1]

Bellar, D., Glickman, E. L., Juvancic-Heltzel, J., & Gunstad, J. ( 2011).

Serum insulin like growth factor-1 is associated with working memory, executive function and selective attention in a sample of healthy, fit older adults

Neuroscience, 178, 133-137.

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Binder, J.R., & Desai, R.H . ( 2011).

The neurobiology of semantic memory

Trends in Cognitive Sciences, 15( 11), 527-536.

URL     PMID:22001867      [本文引用: 1]

Semantic memory includes all acquired knowledge about the world and is the basis for nearly all human activity, yet its neurobiological foundation is only now becoming clear. Recent neuroimaging studies demonstrate two striking results: the participation of modality-specific sensory, motor, and emotion systems in language comprehension, and the existence of large brain regions that participate in comprehension tasks but are not modality-specific. These latter regions, which include the inferior parietal lobe and much of the temporal lobe, lie at convergences of multiple perceptual processing streams. These convergences enable increasingly abstract, supramodal representations of perceptual experience that support a variety of conceptual functions including object recognition, social cognition, language, and the remarkable human capacity to remember the past and imagine the future.

Boyer, D.M., & Harrington, A.R . ( 2018).

Scaling of bony canals for encephalic vessels in euarchontans: Implications for the role of the vertebral artery and brain metabolism

Journal of Human Evolution, 114, 85-101.

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Brehmer, Y., Kalpouzos, G., Wenger, E., & Lövdén, M. ( 2014).

Plasticity of brain and cognition in older adults

Psychological Research, 78( 6), 790-802.

URL     PMID:25261907      [本文引用: 1]

Aging is typically related to changes in brain and cognition, but the aging process is heterogeneous and differs between individuals. Recent research has started investigating the influence of cognitive and physical training on cognitive performance, functional brain activity, and brain structure in old age. The functional relevance of neural changes and the interactions among these changes following interventions is still a matter of debate. Here we selectively review research on structural and functional brain correlates of training-induced performance changes in healthy older adults and present exemplary longitudinal intervention studies sorted by the type of training applied (i.e., strategy-based training, process-specific training, and physical exercise). Although many training studies have been conducted recently, within each task domain, the number of studies that used comparable methods and techniques to assess behavioral and neural changes is limited. We suggest that future studies should include a multimodal approach to enhance the understanding of the relation between different levels of brain changes in aging and those changes that result from training. Investigating inter-individual differences in intervention-induced behavioral and neuronal changes would provide more information about who would benefit from a specific intervention and why. In addition, a more systematic examination of the time course of training-related structural and functional changes would improve the current level of knowledge about how learning is implemented in the brain and facilitate our understanding of contradictory results.

Brehmer, Y., Rieckmann, A., Bellander, M., Westerberg, H., Fischer, H., & Bäckman, L. ( 2011).

Neural correlates of training-related working-memory gains in old age

Neuroimage, 58( 4), 1110-1120.

URL     PMID:21757013      [本文引用: 2]

78 Old persons improved performance after five weeks of adaptive WM training. 78 There was transfer to non-trained tasks (sustained attention, episodic memory). 78 Adaptive training and low-level practice resulted in neocortical BOLD decreases. 78 Greater neural efficiency from training appeared under high task difficulty. 78 The size of gains was linked to cortical BOLD decreases and subcortical increases.

Cao, W., Cao, X., Hou, C., Li, T., Cheng, Y., Jiang, L., ... Yao, D. ( 2016).

Effects of cognitive training on resting-state functional connectivity of default mode, salience, and central executive networks

Frontiers in Aging Neuroscience, 8, 70.

[本文引用: 2]

Cao, X. Y., Yao, Y., Li, T., Cheng, Y., Feng, W., Shen, Y., ... Li, C. B. ( 2016).

The impact of cognitive training on cerebral white matter in community-dwelling elderly: One-year prospective longitudinal diffusion tensor imaging study

Scientific Reports, 6( 33212).

URL     [本文引用: 1]

Carlén, M.( 2017).

What constitutes the prefrontal cortex?

Science, 358( 6362), 478-482.

URL     [本文引用: 2]

Carlson, M. C., Erickson, K. I., Kramer, A. F., Voss, M. W., Bolea, N., Mielke, M., ... Fried, L. P. ( 2009).

Evidence for neurocognitive plasticity in at-risk older adults: The Experience Corps program

Journals of Gerontology - Series A Biological Sciences and Medical Sciences, 64( 12), 1275-1282.

URL     PMID:19692672      [本文引用: 2]

To determine whether Experience Corps (EC), a social service program, would improve age-vulnerable executive functions and increase activity in brain regions in a high-risk group through increased cognitive and physical activity. Eight community-dwelling, older female volunteers and nine matched wait-list controls were recruited to serve in the ongoing EC: Baltimore program in three elementary schools. We employed functional magnetic resonance imaging (fMRI) preintervention and postintervention to examine whether EC volunteers improved executive function and showed increased activity in the prefrontal cortex relative to controls. fMRI volunteers were trained and placed with other volunteers 15 h/wk for 6 months during the academic year to assist teachers in kindergarten through third grade to promote children's literacy and academic achievement. Participants were African American and had low education, low income, and low Mini-Mental State Examination scores (M = 24), indicative of elevated risk for cognitive impairment. Volunteers exhibited intervention-specific increases in brain activity in the left prefrontal cortex and anterior cingulate cortex over the 6-month interval relative to matched controls. Neural gains were matched by behavioral improvements in executive inhibitory ability. Using fMRI, we demonstrated intervention-specific short-term gains in executive function and in the activity of prefrontal cortical regions in older adults at elevated risk for cognitive impairment. These pilot results provide proof of concept for use-dependent brain plasticity in later life, and, that interventions designed to promote health and function through everyday activity may enhance plasticity in key regions that support executive function.

Castro-Chavira, S. A., Barrios, F. A., Pasaye, E. H., Alatorre- Cruz, G. C., & Fernández, T. ( 2016).

Compensatory larger cortical thickness in healthy elderly individuals with electroencephalographic risk for cognitive decline

Neuroreport, 27( 9), 710-715.

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Chapman, S. B., Aslan, S., Spence, J. S., Hart, J. J., Jr., Bartz, E. K., Didehbani, N., ... Lu, H. ( 2015).

Neural mechanisms of brain plasticity with complex cognitive training in healthy seniors

Cerebral Cortex, 25( 2), 396-405.

URL     PMID:23985135      [本文引用: 2]

Complex mental activity induces improvements in cognition, brain function, and structure in animals and young adults. It is not clear to what extent the aging brain is capable of such plasticity. This study expands previous evidence of generalized cognitive gains after mental training in healthy seniors. Using 3 MRI-based measurements, that is, arterial spin labeling MRI, functional connectivity, and diffusion tensor imaging, we examined brain changes across 3 time points pre, mid, and post training (12 weeks) in a randomized sample (n= 37) who received cognitive training versus a control group. We found significant training-related brain state changes at rest; specifically, 1) increases in global and regional cerebral blood flow (CBF), particularly in the default mode network and the central executive network, 2) greater connectivity in these same networks, and 3) increased white matter integrity in the left uncinate demonstrated by an increase in fractional anisotropy. Improvements in cognition were identified along with significant CBF correlates of the cognitive gains. We propose that cognitive training enhances resting-state neural activity and connectivity, increasing the blood supply to these regions via neurovascular coupling. These convergent results provide preliminary evidence that neural plasticity can be harnessed to mitigate brain losses with cognitive training in seniors.

Cheng, Y., Wu, W. Y., Feng, W., Wang, J. Q., Chen, Y., Shen, Y., ... Li, C. B. ( 2012).

The effects of multi-domain versus single-domain cognitive training in non-demented older people: A randomized controlled trial

Bmc Medicine, 10(30).

[本文引用: 1]

Chooi, W.-T., & Thompson, L.A. ( 2012).

Working memory training does not improve intelligence in healthy young adults

Intelligence, 40( 6), 531-542.

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Colcombe, S. J., Erickson, K. I., Scalf, P. E., Kim, J. S., Prakash, R., McAuley, E., ... Kramer, A. F. ( 2006).

Aerobic exercise training increases brain volume in aging humans. The

Journals of Gerontology: Series A 61( 11), 1166-1170.

[本文引用: 1]

Dahlin, E., Neely, A. S., Larsson, A., Bäckman, L., & Nyberg, L. ( 2008).

Transfer of learning after updating training mediated by the striatum

Science, 320( 5882), 1510-1512.

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de Melo Coelho, F. G., Vital, T. M., Stein, A. M., Arantes, F. J., Rueda, A. V., Camarini, R., ... Santos-Galduróz, R. F. ( 2014).

Acute aerobic exercise increases brain-derived neurotrophic factor levels in elderly with Alzheimer's disease. Journal of Alzheimer's

Disease, 39(2), 401-408.

[本文引用: 1]

Donoso, M., Collins, A. G. E., & Koechlin, E. ( 2014).

Foundations of human reasoning in the prefrontal cortex

Science, 344( 6191), 1481-1486.

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Eggenberger, P., Wolf, M., Schumann, M., & de Bruin, E. D.( 2016).

Exergame and balance training modulate prefrontal brain activity during walking and enhance executive function in older adults

Frontiers in Aging Neuroscience, 8, 66.

[本文引用: 1]

Engvig, A., Fjell, A. M., Westlye, L. T., Moberget, T., Sundseth, Ø., Larsen, V. A., & Walhovd, K. B. ( 2010).

Effects of memory training on cortical thickness in the elderly

Neurolmage, 52( 4), 1667-1676.

URL     PMID:20580844      [本文引用: 1]

The brain's ability to alter its functional and structural architecture in response to experience and learning has been extensively studied. Mental stimulation might serve as a reserve mechanism in brain aging, but macrostructural brain changes in response to cognitive training have been demonstrated in young participants only. We examined the short-term effects of an intensive memory training program on cognition and brain structure in middle-aged and elderly healthy volunteers. The memory trainers completed an 8-week training regimen aimed at improving verbal source memory utilizing the Method of Loci (MoL), while control participants did not receive any intervention. Both the memory trainers and the controls underwent magnetic resonance imaging (MRI) scans and memory testing pre and post 8聽weeks of training or no training, respectively. Cortical thickness was automatically measured across the cortical mantle, and data processing and statistical analyses were optimized for reliable detection of longitudinal changes. The results showed that memory training improved source memory performance. Memory trainers also showed regional increases in cortical thickness compared with controls. Furthermore, thickness change in the right fusiform and lateral orbitofrontal cortex correlated positively with improvement in source memory performance, suggesting a possible functional significance of the structural changes. These findings demonstrate that systematic mental exercise may induce short-term structural changes in the aging human brain, indicating structural brain plasticity in elderly. The present study included short-term assessments, and follow-up studies are needed in order to assess whether such training indeed alters the long-term structural trajectories.

Engvig, A., Fjell, A. M., Westlye, L. T., Moberget, T., Sundseth, Ø., Larsen, V. A., & Walhovd, K. B. ( 2012).

Memory training impacts short-term changes in aging white matter: A longitudinal diffusion tensor imaging study

Human Brain Mapping, 33( 10), 2390-2406.

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Erickson, K. I., Leckie, R. L., & Weinstein, A. M. ( 2014).

Physical activity, fitness, and gray matter volume

Neurobiology of Aging, 35( Suppl. 2), S20-S28.

URL     PMID:4094356     

In this review, we explore the association among physical activity, cardiorespiratory fitness, and exercise on gray matter volume in older adults. We conclude that higher cardiorespiratory fitness levels are routinely associated with greater gray matter volume in the prefrontal cortex and hippocampus and less consistently in other regions. We also conclude that physical activity is associated with greater gray matter volume in the same regions that are associated with cardiorespiratory fitness including the prefrontal cortex and hippocampus. Some heterogeneity in the literature may be explained by effect moderation by age, stress, or other factors. Finally, we report promising results from randomized exercise interventions that suggest that the volume of the hippocampus and prefrontal cortex remain pliable and responsive to moderate intensity exercise for 6 months 1 year. Physical activity appears to be a propitious method for influencing gray matter volume in late adulthood, but additional well-controlled studies are necessary to inform public policies about the potential protective or therapeutic effects of exercise on brain volume.

Erickson, K. I., Weinstein, A. M., Sutton, B. P., Prakash, R. S., Voss, M. W., Chaddock, L., ... Kramer, A. F. ( 2012).

Beyond vascularization: Aerobic fitness is associated with N-acetylaspartate and working memory

Brain and Behavior, 2( 1), 32-41.

URL     PMID:3343297      [本文引用: 1]

Aerobic exercise is a promising form of prevention for cognitive decline; however, little is known about the molecular mechanisms by which exercise and fitness impacts the human brain. Several studies have postulated that increased regional brain volume and function are associated with aerobic fitness because of increased vascularization rather than increased neural tissue per se. We tested this position by examining the relationship between cardiorespiratory fitness and N-acetylaspartate (NAA) levels in the right frontal cortex using magnetic resonance spectroscopy. NAA is a nervous system specific metabolite found predominantly in cell bodies of neurons. We reasoned that if aerobic fitness was predominantly influencing the vasculature of the brain, then NAA levels should not vary as a function of aerobic fitness. However, if aerobic fitness influences the number or viability of neurons, then higher aerobic fitness levels might be associated with greater concentrations of NAA. We examined NAA levels, aerobic fitness, and cognitive performance in 137 older adults without cognitive impairment. Consistent with the latter hypothesis, we found that higher aerobic fitness levels offset an age-related decline in NAA. Furthermore, NAA mediated an association between fitness and backward digit span performance, suggesting that neuronal viability as measured by NAA is important in understanding fitness-related cognitive enhancement. Since NAA is found exclusively in neural tissue, our results indicate that the effect of fitness on the human brain extends beyond vascularization; aerobic fitness is associated with neuronal viability in the frontal cortex of older adults.

Fjell, A. M., Sneve, M. H., Grydeland, H., Storsve, A. B., & Walhovd, K. B. ( 2016).

The disconnected brain and executive function decline in aging

Cerebral Cortex, 27( 3), 2303-2317.

[本文引用: 1]

Goulden, N., Khusnulina, A., Davis, N. J., Bracewell, R. M., Bokde, A. L., McNulty, J. P., & Mullins, P. G. ( 2014).

The salience network is responsible for switching between the default mode network and the central executive network: Replication from DCM

Neurolmage, 99, 180-190.

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Grady, C.( 2012).

The cognitive neuroscience of ageing

Nature Reviews Neuroscience, 13, 491-505.

URL     PMID:22714020      [本文引用: 2]

The availability of neuroimaging technology has spurred a marked increase in the human cognitive neuroscience literature, including the study of cognitive ageing. Although there is a growing consensus that the ageing brain retains considerable plasticity of function, currently measured primarily by means of functional MRI, it is less clear how age differences in brain activity relate to cognitive performance. The field is also hampered by the complexity of the ageing process itself and the large number of factors that are influenced by age. In this Review, current trends and unresolved issues in the cognitive neuroscience of ageing are discussed.

Gray, J. R., Chabris, C. F., & Braver, T. S. ( 2003).

Neural mechanisms of general fluid intelligence

Nature Neuroscience, 6( 3), 316-322.

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Håkansson, K., Ledreux, A., Daffner, K., Terjestam, Y., Bergman, P., Carlsson, R., ... Mohammed, A. K. H.( 2017).

BDNF responses in healthy older persons to 35 minutes of physical exercise, cognitive training, and mindfulness: Associations with working memory function

Journal of Alzheimer's Disease, 55( 2), 645-657.

[本文引用: 1]

Haskell, W. L., Lee, I.-M., Pate, R. R., Powell, K. E., Blair, S. N., Franklin, B. A., ... Bauman, A. ( 2007).

Physical activity and public health: Updated recommendation for adults from the American College of Sports Medicine and the American Heart Association

Medicine and Science in Sports and Exercise, 39( 8), 1423-1434.

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Heinzel, S., Lorenz, R. C., Brockhaus, W.-R., Wüstenberg, T., Kathmann, N., Heinz, A., & Rapp, M. A. ( 2014).

Working memory load-dependent brain response predicts behavioral training gains in older adults

Journal of Neuroscience, 34( 4), 1224-1233.

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Heinzel, S., Lorenz, R. C., Pelz, P., Heinz, A., Walter, H., Kathmann, N., ... Stelzel, C. ( 2016).

Neural correlates of training and transfer effects in working memory in older adults

Neurolmage, 134, 236-249.

URL     PMID:27046110      [本文引用: 1]

61Working memory training leads to neural activation decrease in the right MFG in aging.61Neural changes in transfer task are related to updating (compared to maintenance).61Neural correlates of training and transfer effects overlap in the right MFG.61Behavioral transfer to executive functions, processing speed, fluid intelligence61Results advance understanding of neural mechanisms of training and transfer.

Heinzel, S., Riemer, T. G., Schulte, S., Onken, J., Heinz, A., & Rapp, M. A. ( 2014).

Catechol-O-methyltransferase (COMT) genotype affects age-related changes in plasticity in working memory: A pilot study

BioMed Research International, 2014, ( 414351), 7.

[本文引用: 1]

Hötting, K., Reich, B., Holzschneider, K., Kauschke, K., Schmidt, T., Reer, R., ... Roder, B. ( 2012).

Differential cognitive effects of cycling versus stretching/coordination training in middle-aged adults

Health Psychology, 31( 2), 145-155.

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Hötting, K., & Roder, B.( 2013).

Beneficial effects of physical exercise on neuroplasticity and cognition

Neuroscience & Biobehavioral Reviews, 37( 9), 2243-2257.

[本文引用: 1]

Jaeggi, S. M., Buschkuehl, M., Jonides, J., & Perrig, W. J. ( 2008).

Improving fluid intelligence with training on working memory

PNAS, 105( 19), 6829-6833.

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Ji, Y., Wang, J., Chen, T., Du, X., & Zhan, Y. ( 2016).

Plasticity of inhibitory processes and associated far- transfer effects in older adults

Psychology and aging, 31( 5), 415-429.

URL     PMID:27243762      [本文引用: 3]

Abstract Inhibition deficit plays a crucial part in cognitive aging; however, few studies have systematically investigated the plasticity of various inhibitory processes among older adults. We studied the plasticity of 3 inhibitory processes (access, deletion, and restraint) and the extent of far transfer of inhibition training to other general cognitive abilities. Thirty-six participants (aged 60 years and above, M = 70.06, SD = 5.53) were randomly assigned to an adaptive training group that received 12 sessions of training covering 3 inhibitory processes or an active control group that received 4 sessions of mental health lectures. Participants in both groups completed pre- and posttest assessments, in which behavioral and electrophysiological measures were used to evaluate potential transfer effects. Direct training gains were observed for trained tasks of all inhibitory processes, but near-transfer effects were only found within untrained tasks associated with deletion at a composite score level. Furthermore, far-transfer effects were demonstrated for fluid intelligence (Gf) but not for working memory or other general cognitive abilities. Near transfer to deletion and far transfer to Gf persisted at a 3-month follow-up assessment session. We discussed differences in plasticity between the 3 inhibitory processes as well as their possible associations with far transfer to Gf. (PsycINFO Database Record (c) 2016 APA, all rights reserved).

Jiang, L. J., Cao, X. Y., Li, T., Tang, Y. Y., Li, W., Wang, J. J., ... Li, C. B. ( 2016).

Cortical thickness changes correlate with cognition changes after cognitive training: Evidence from a Chinese community study

Frontiers in Aging Neuroscience, 8, 118.

[本文引用: 2]

Kim, G. H., Jeon, S., Im, K., Kwon, H., Lee, B. H., Kim, G. Y., ... Na, D. L. ( 2015).

Structural brain changes after traditional and robot-assisted multi-domain cognitive training in community-dwelling healthy elderly

PLoS One, 10( 4), e0123251.

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Li, R., Zhu, X. Y., Yin, S. F., Niu, Y. N., Zheng, Z. W., Huang, X., ... Li, J. ( 2014).

Multimodal intervention in older adults improves resting-state functional connectivity between the medial prefrontal cortex and medial temporal lobe

Frontiers in Aging Neuroscience, 6, 39.

[本文引用: 2]

Lin, F., Heffner, K. L., Ren, P., Tivarus, M. E., Brasch, J., Chen, D. G., ... Tadin, D. ( 2016).

Cognitive and neural effects of vision-based speed-of-processing training in older adults with amnestic mild cognitive impairment: A pilot study

Journal of the American Geriatrics Society, 64( 6), 1293-1298.

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Lindenberger, U.( 2014).

Human cognitive aging: Corriger la fortune?

Science, 346( 6209), 572-578.

URL     PMID:25359964      [本文引用: 1]

Abstract Human cognitive aging differs between and is malleable within individuals. In the absence of a strong genetic program, it is open to a host of hazards, such as vascular conditions, metabolic syndrome, and chronic stress, but also open to protective and enhancing factors, such as experience-dependent cognitive plasticity. Longitudinal studies suggest that leading an intellectually challenging, physically active, and socially engaged life may mitigate losses and consolidate gains. Interventions help to identify contexts and mechanisms of successful cognitive aging and give science and society a hint about what would be possible if conditions were different. Copyright 2014, American Association for the Advancement of Science.

Littlefield, A. M., Setti, S. E., Priester, C., & Kohman, R. A. ( 2015).

Voluntary exercise attenuates LPS-induced reductions in neurogenesis and increases microglia expression of a proneurogenic phenotype in aged mice

Journal of Neuroinflammation, 12( 1), 138.

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Lövdén, M., Bodammer, N. C., Kühn, S., Kaufmann, J., Schütze, H., Tempelmann, C., ... Lindenberger, U. ( 2010).

Experience-dependent plasticity of white-matter microstructure extends into old age

Neuropsychologia, 48( 13), 3878-3883.

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Luo, C., Zhang, X., Cao, X., Gan, Y., Li, T., Cheng, Y., ... Li, C. ( 2016).

The lateralization of intrinsic networks in the aging brain implicates the effects of cognitive training

Frontiers in Aging Neuroscience, 8, 32.

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Luszcz, M . ( 2011).

Executive function and cognitive aging

In K. Schaie & S. Willis (Eds.), Handbook of the psychology of aging (7th ed) (pp. 59-72). San Diego, CA: Academic Press.

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Mander, B. A., Rao, V., Lu, B., Saletin, J. M., Lindquist, J. R., Ancoli-Israel, S., ... Walker, M. P. ( 2013).

Prefrontal atrophy, disrupted NREM slow waves and impaired hippocampal-dependent memory in aging

Nature Neuroscience, 16( 3), 357-364.

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McNab, F., Varrone, A., Farde, L., Jucaite, A., Bystritsky, P., Forssberg, H., & Klingberg, T. ( 2009).

Changes in cortical dopamine D1 receptor binding associated with cognitive training

Science, 323( 5915), 800-802.

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Melby-Lervåg, M., & Hulme, C.( 2016).

There is no convincing evidence that working memory training is effective: A reply to Au et al. (2014) and Karbach and Verhaeghen (2014)

Psychonomic Bulletin & Review, 23( 1), 324-330.

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Metzler-Baddeley, C., Foley, S., de Santis, S., Charron, C., Hampshire, A., Caeyenberghs, K., & Jones, D. K. ( 2017).

Dynamics of white matter plasticity underlying working memory training: Multimodal evidence from diffusion MRI and T2 relaxometry

Journal of Cognitive Neuroscience, 29( 9), 1-12.

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Mishra, J., de Villers-Sidani, E., Merzenich, M., & Gazzaley, A. ( 2014).

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In parallel rat and human experiments, Mishra et02al. show how adaptive reinforcement training can be used in a targeted manner to harness neuroplasticity at multiple neural scales, selectively improve distractor-suppression in aging, and further benefit cognitive control.

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In R. Dixon, L. Backman, & L.-G. Nilsson (Eds.), New Frontiers in Cognitive Aging (pp. 115-134). Oxford University Press.

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Ruscheweyh, R., Willemer, C., Krüger, K., Duning, T., Warnecke, T., Sommer, J., ... Flöel, A. ( 2011).

Physical activity and memory functions: An interventional study

Neurobiology of Aging, 32( 7), 1304-1319.

URL     PMID:19716631      [本文引用: 1]

Previous studies have suggested beneficial effects of physical activity on cognition. Here, we asked in an interventional approach if physical activity performed at different intensity levels would differentially affect episodic memory function. Additionally, we tried to identify mechanisms mediating these changes. Sixty-two healthy elderly individuals were assessed for level of physical activity, aerobic fitness, episodic memory score, neurotrophin and catecholamine levels, and received a magnetic resonance image of the brain at baseline and after a six months intervention of medium or low-intensity physical activity or control. Increase in total physical activity was positively associated with increase in memory score over the entire cohort, without significant differences between intensity groups. It was also positively associated with increases in local gray matter volume in prefrontal and cingulate cortex, and BDNF levels (trend). In conclusion, we showed that physical activity conveys the beneficial effects on memory function independently of its intensity, possibly mediated by local gray matter volume and neurotrophic factors. Our findings may carry significant implications for prevention of cognitive decline in the elderly.

Schättin, A., Arner, R., Gennaro, F., & de Bruin, E. D.( 2016).

Adaptations of prefrontal brain activity, executive functions, and gait in healthy elderly following exergame and balance training: A randomized-controlled study

Frontiers in Aging Neuroscience, 8, 278.

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Serum basal hormone concentrations, nutrition and physical fitness during strength and/or endurance training in 39-64-year- old women

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Intense exercise promotes adult hippocampal neurogenesis but not spatial discrimination

Frontiers in Cellular Neuroscience, 11, 13.

Suzuki, T., Shimada, H., Makizako, H., Doi, T., Yoshida, D., Ito, K., Kato, T. (2013).

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Acute effects of physical exercise on prefrontal cortex activity in older adults: A functional near-infrared spectroscopy study

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Viboolvorakul, S., & Patumraj, S.( 2014).

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Voelcker-Rehage, C., Godde, B., & Staudinger, U. M. ( 2011).

Cardiovascular and coordination training differentially improve cognitive performance and neural processing in older adults

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Wen, W., Zhu, W. L., He, Y., Kochan, N. A., Reppermund, S., Slavin, M. J., ... Sachdev, P. ( 2011).

Discrete neuroanatomical networks are associated with specific cognitive abilities in old age

Journal of Neuroscience, 31( 4), 1204-1212.

URL     PMID:21273405     

There have been many attempts at explaining on the basis of regional brain changes, with the usual but inconsistent findings being that smaller gray matter volumes in certain brain regions predict worse cognitive performance in specific domains. Additionally, compromised white matter integrity, as suggested by white matter hyperintensities or decreased regional white matter fractional anisotropy, has an adverse impact on cognitive functions. The brain is, however, a network and it may be more appropriate to relate cognitive functions to properties of the network rather than specific brain regions. We report on graph theory-based analyses of diffusion tensor imaging tract-derived connectivity in a sample of 342 healthy individuals aged 72-92 years. The cognitive domains included processing speed, , language, visuospatial, and executive functions. We examined the association of these cognitive assessments with both the connectivity of the whole brain network and individual cortical regions. We found that the efficiency of the whole brain network of cortical fiber connections had an influence on processing speed and visuospatial and executive functions. Correlations between connectivity of specific regions and cognitive assessments were also observed, e.g., stronger connectivity in regions such as superior frontal gyrus and posterior cingulate cortex were associated with better executive function. Similar to the relationship between regional connectivity efficiency and age, greater processing speed was significantly correlated with better connectivity of nearly all the cortical regions. For the first time, regional anatomical connectivity maps related to processing speed and visuospatial and executive functions in the elderly are identified.

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An application of prefrontal cortex function theory to cognitive aging

Psychological Bulletin, 120( 2), 272-292.

URL     PMID:8831298      [本文引用: 2]

Abstract The purpose of this review is to extend the existing application of the frontal lobe hypothesis of cognitive aging beyond the limited work on inhibitory control (F. N. Dempster, 1992) to include memory processes supported by the prefrontal cortex. To establish a background for this analysis, I review existing models of prefrontal cortex function and present a synthesized model that includes a general function of temporal integration, supported by 4 specific processes: prospective memory, retrospective memory, interference control, and inhibition of prepotent responses. I found the frontal lobe hypothesis to perform well, with the exception of an inability to account for age-related declines in item recall and recognition memory, possibly a result of age-related declines in medial temporal function.

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