Alm Per A
Department of Neuroscience, Uppsala University, Uppsala, Sweden.
Front Hum Neurosci. 2021 Dec 2;15:661880. doi: 10.3389/fnhum.2021.661880. eCollection 2021.
The last decades of research have gradually elucidated the complex functions of the dopamine system in the vertebrate brain. The multiple roles of dopamine in motor function, learning, attention, motivation, and the emotions have been difficult to reconcile. A broad and detailed understanding of the physiology of cerebral dopamine is of importance in understanding a range of human disorders. One of the core functions of dopamine involves the basal ganglia and the learning and execution of automatized sequences of movements. Speech is one of the most complex and highly automatized sequential motor behaviors, though the exact roles that the basal ganglia and dopamine play in speech have been difficult to determine. Stuttering is a speech disorder that has been hypothesized to be related to the functions of the basal ganglia and dopamine. The aim of this review was to provide an overview of the current understanding of the cerebral dopamine system, in particular the mechanisms related to motor learning and the execution of movement sequences. The primary aim was not to review research on speech and stuttering, but to provide a platform of neurophysiological mechanisms, which may be utilized for further research and theoretical development on speech, speech disorders, and other behavioral disorders. Stuttering and speech are discussed here only briefly. The review indicates that a primary mechanism for the automatization of movement sequences is the merging of isolated movements into chunks that can be executed as units. In turn, chunks can be utilized hierarchically, as building blocks of longer chunks. It is likely that these mechanisms apply also to speech, so that frequent syllables and words are produced as motor chunks. It is further indicated that the main learning principle for sequence learning is reinforcement learning, with the phasic release of dopamine as the primary teaching signal indicating successful sequences. It is proposed that the dynamics of the dopamine system constitute the main neural basis underlying the situational variability of stuttering.
过去几十年的研究逐渐阐明了多巴胺系统在脊椎动物大脑中的复杂功能。多巴胺在运动功能、学习、注意力、动机和情感方面的多重作用一直难以协调。对大脑多巴胺生理学进行广泛而详细的了解对于理解一系列人类疾病至关重要。多巴胺的核心功能之一涉及基底神经节以及自动运动序列的学习和执行。言语是最复杂且高度自动化的连续运动行为之一，尽管基底神经节和多巴胺在言语中的确切作用一直难以确定。口吃是一种言语障碍，据推测与基底神经节和多巴胺的功能有关。本综述的目的是概述目前对大脑多巴胺系统的理解，特别是与运动学习和运动序列执行相关的机制。主要目的不是回顾关于言语和口吃的研究，而是提供一个神经生理机制平台，可用于对言语、言语障碍和其他行为障碍的进一步研究和理论发展。这里仅简要讨论口吃和言语。综述表明，运动序列自动化的主要机制是将孤立的动作合并为可作为单元执行的组块。反过来，组块可以分层使用，作为更长组块的构建块。这些机制可能也适用于言语，因此频繁出现的音节和单词作为运动组块产生。进一步表明，序列学习的主要学习原则是强化学习，多巴胺的阶段性释放作为表明序列成功的主要教学信号。有人提出，多巴胺系统的动态变化构成了口吃情境变异性的主要神经基础。
