注意力不足过动症的病理生理学
![](http://upload.wikimedia.org/wikipedia/commons/thumb/6/64/Synapse_dopaminergique.png/220px-Synapse_dopaminergique.png)
关于注意力不足过动症的病理生理学,截至公元2019年7月底,注意力不足过动症(ADHD)被认为是肇因于部分脑内的神经传导物质系统的损伤(特别是与多巴胺和正肾上腺素有关的神经传导系统),进而对患者的脑部执行功能产生不良的影响。[1][2]多巴胺与正肾上腺素的脑内神经通道大多起源自脑内的腹侧被盖区和蓝斑核,并由此投射至不同的脑区且管理许多认知的流程(与认知功能相关的处理流程)。[1][3]特别是那些投射至前额叶和纹状体的脑内多巴胺通道和脑内正肾上腺素通道/蓝斑核系统。它们主要的工作就是负责调节执行功能(认知和行为的功能与管理)、动机、 酬赏/报偿的感受能力、和运动神经的功能[注 1]。[1][2][3]以上是目前已知在注意力不足过动症的病理生理学中扮演主要脚色的几条脑内神经通道。也已经有人提议强化对于注意力不足过动症更全面的概观以及更多可能与之相关的脑内神经通道之探究。[2][5][6]
大脑结构
[编辑]![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/94/Attention_deficit_hyperactivity_disorder_-_Attention_deficit_hyperactivity_disorder_-_Reduced_brain_volume_on_the_left_side_from_ADHD.jpg/220px-Attention_deficit_hyperactivity_disorder_-_Attention_deficit_hyperactivity_disorder_-_Reduced_brain_volume_on_the_left_side_from_ADHD.jpg)
在儿童注意力不足过动症患者中,普遍存有一些脑部结构(特别是左侧的前额叶、后顶叶皮质)在体积上小于平均值的现象。[2][7]其他诸如注意力不足过动症患者的:前额 - 纹状体-小脑和前额叶-纹状体-丘脑回路也被发现与非注意力不足过动症患者不同。[2][5][6]
ADHD儿童的双侧额叶、顶叶和颞叶灰质体积小于同样正在发育中的非ADHD儿童,ADHD儿童的脑部构造跟对照组(同样正在发育中的非ADHD儿童)相比后,体积差异最大的部分是右额叶和左颞叶。进一步检视实验组(ADHD儿童)与对照组(非ADHD儿童)的额叶子区域后发现,实验组与对照组彼此之间的左侧眶额叶皮质、左侧初级运动皮层(M1)、和左侧运动辅助区(SMC)体积差异最大。[8] 与“特定亚区(左前额叶、左前叶、左额叶、M1和右SMC)相关的ADHD关联程度”跟“ADHD症状的严重程度”成反比,举例来说:当前述皮层的体积越小则“过动—冲动”症状的严重程度越高,前述皮层的体积与“过动—冲动”症状的严重程度成反比。[8]ADHD个案组在伏隔核、海马回、杏仁核、基底核、颅内等区域之体积皆有较健康控制组(非ADHD儿童)更小的体积;实验组(ADHD儿童)与对照组(非ADHD儿童)在苍白球与丘脑的体积相比之下则没有在统计学上达到显著差异。进一步分析发现,在大部分区域(包括杏仁核、基底核、伏隔核、海马回),小于15岁的ADHD孩童与健康发展孩童(非ADHD儿童)的脑体积差异程度,较持续到成人的ADHD患者(大于21岁)与健康受试成人(非ADHD成人)的比较差异程度来得大,这暗示著ADHD患者之大脑发展迟缓的现象。[9]
另外,目前学术界对于ADHD药物治疗是否会对于ADHD患者的大脑内部结构体积产生改变,出现了不一致的研究结果。[9]
研究发现,ADHD青少年患者脑中的白质路径(white matter tracts)存在不对称的情况,这可能表示患者脑中各脑区的整合于连动发展出现不一致的问题,这样的问题或许与ADHD患者的行为模式相关联。[10]
神经传导物质的通道/路径
[编辑]目前的研究模型包含了 中脑皮质素-多巴胺通道 及蓝斑核-去甲肾上腺素系统。[1][2][3]用于治疗注意力不足过动症的中枢神经刺激剂,其疗效可能是起因于它增进了神经传导物质在这些系统中的活动。[2][3][11]注意力不足过动症患者脑部中的 5-羟色胺能(与血清素有关)通道、 谷氨酸能(一种神经传导物质)通道、 或胆碱能通道可能也存有一些导致注意力不足过动症症状的原因。[11][12][13]
另有研究发现,注意力不足过动症是由一种发生于脑前额叶的遗传性的多巴胺新陈代谢失常有关[14][15][16]。更近期的研究认为正肾上腺素的新陈代谢亦会对病情有所影响[16]。
![](http://upload.wikimedia.org/wikipedia/commons/4/40/Adhdbrain.png)
利用核磁共振成像技术(MRI)对脑部扫描的研究显示患有ADHD和非ADHD的孩子的图象有分别。不少科学家认为这足以证明ADHD是和脑部创伤有关。但脑部影像只说明了作为脑内燃料的葡萄糖的分布。在成人ADHD患者的脑扫描中,控制专注力的部分由于葡萄糖水平较低,所以显得不太活跃。不过,没有证据显示低葡萄糖水平与注意力缺陷有关联,亦无法推论两者之间的因果关系。[17]
执行功能和动机
[编辑]注意力不足过动症的症状起因于某些执行功能上的缺陷,例如:注意力/专注力的控制、冲动-过动控制、及工作记忆。[19][2][3][20]执行功能简单来说就是一整群包含认知处理过程的集合[a]。而这集合必须能够成功的帮助一个人选择并督促自己做出得以实现他那经过深思熟虑过后的目标之行为。[19][3][20]执行功能也帮助一个人能适当的应对新奇、复杂、全面、或模棱两可的情况[21][22]。
注意力不足过动症患者先天的执行功能损伤造成以下这些症状:难以维持有规划的、难以有组织性的、缺乏时间观念、过度的拖延、难以保持专注、难以把注意力放对地方、难以忽略与任务不相干的外务/诱惑、有情绪管理的困难、难以把细节记起来。[19][2][3]注意力不足过动症患者在长期记忆的表现可看出注意力不足过动症患者的长期记忆是没有损伤的。注意力不足过动症患者在提取长期记忆时所产生的困难显然是肇因于工作记忆[b]的受损[19][23]。 端视一个注意力不足过动症患者其脑部发展的程度与其所在环境对其执行功能要求的程度的比例,因此有些注意力不足过动症患者可能直到青少年时期甚至是成年期(特别是成年初期)才开始显露出注意力不足过动症的症状。[19][24][25][26]
注意力不足过动症与患者在儿童青少年乃至成年时期缺乏动机相关。儿童青少年甚至成人注意力不足过动症患者会发现自己比起眼前立即的回馈、酬赏、或满足,更难以专注在长远的目标、回报、回馈、酬赏、或满足,并展现出对于眼前立即的回馈、酬赏、或满足的冲动言行。[27]
注释
[编辑]备注
[编辑]参见
[编辑]文献来源
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NOTE: DA: dopamine, LC: locus coeruleus, VTA: ventral tegmental area, 5HT: serotonin (5-hydroxytryptamine) - ^ 高淑芬. 找回專注力:成人ADHD全方位自助手冊. 博客来. 2016-05-09 [2018-09-03]. (原始内容存档于2016-11-30) (中文).
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Recent conceptualizations of ADHD have taken seriously the distributed nature of neuronal processing [10,11,35,36]. Most of the candidate networks have focused on prefrontal-striatal-cerebellar circuits, although other posterior regions are also being proposed [10].
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Executive function (EF) is an umbrella term that encompasses the set of higher-order processes (such as inhibitory control, working memory, and attentional flexibility) that govern goal-directed action and adaptive responses to novel, complex, or ambiguous situations (Hughes et al., 2005).
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Some adults present with impairment in a clinical setting only later in life when they confront new and increasingly complex tasks that characterize adulthood and that cannot be managed with their existing neuropsychological repertoire.
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Previous studies suggest that a clinical approach using interventions to improve motivational processes in patients with ADHD may improve outcomes as children with ADHD transition into adolescence and adulthood.
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