时间认知的脑机制研究

从神经心理学和脑成像2个领域综述了有关时间认知脑机制的研究。神经心理学及脑损伤的研究结果表明小脑可能与内部时钟功能有关,前额叶可能调节时间认知中的注意过程。PET和fMRI脑成象研究结果显示,基底神经节、小脑和前额叶在所有的计时作业中都被激活。ERP的研究结果还证实,时间信息加工和非时间信息加工存在时间历程上的差异,并且时间信息加工还存在的显著半球优势效应。因此基底神经节、小脑和前额叶可能是时间认知的主要脑机制,但由于研究材料、方法和程序的不同,大脑皮层的广泛区域都有可能参与时间信息的加工。     

标量计时模型中的神经机制

标量计时模型中各阶段的神经机制有重叠也有分离。从当今认知神经科学的研究结果看,与内部时钟有关的神经结构有小脑、基底神经节、前额皮质、前运动辅助皮质及顶叶下回皮质等;与记忆阶段有关的神经结构有基底神经节、背外侧前额皮质、右侧额下皮质及外侧前运动皮质等;与决策阶段有关的神经结构有背外侧前额皮质、前扣带回、高级颞叶皮质和基底神经节等。文章还从神经机制角度论证了计时的标量特性,讨论了今后研究值得注意的三个问题,即研究结果的确定性、研究手段的局限性以及该模型的适用性     

左侧前额叶语言加工功能研究综述

1 引言 探讨左前额叶的认知功能是目前脑成像研究的焦点之一。前额叶皮层占人类大脑的1/3。70年代初,鲁利亚提出大脑的三个机能系统时认为,额叶属于第三机能系统,负责编制行为程序,调节、控制行为,它对于完成很多高级认知加工,如计划、控制、问题解决等有着重要作用。近年来不断有研究发现,左侧前额叶还参与了许多和语言加工有关的活动,特别是额下回、Broca区等大脑区域被研究者进行了广泛地探讨。     

工作记忆对时间加工的影响

非时间信息加工与时间加工的关系是复杂的, 存在双向干扰或单向干扰, 结果的不一致与任务所需的注意资源及工作记忆都有关。工作记忆的中央执行系统在时间加工中起主要作用, 同时进行的非时间任务对中央执行功能的需求越多, 两种任务之间的干扰程度越大。语言环和视空间模板对时间加工的影响与非时间信息的类型有关。工作记忆作为一个整体以工作记忆容量为指标, 计时成绩也表现出与工作记忆容量有关的年龄、智力等方面的差异。时间加工和工作记忆在额叶、顶叶、基底神经节等皮质存在共同的神经机制。未来应该丰富工作记忆的研究内容, 结合时间加工的分段性探讨工作记忆影响时间加工的具体进程及神经机制, 并力求在应用方面取得一定的成果。     

元认知的神经机制:元认知功能、脑区与脑网络

元认知是指个体对当前进行的认知活动的监测和调节。通过对元认知神经机制研究的梳理,归纳出两条研究主线:一条主线以具体元认知加工的脑区激活研究为主,主要考察元认知与认知过程的分离及典型元认知加工的共享性和特异性。研究发现元认知加工主要与前额叶有关,还涉及脑岛、顶叶、颞叶和楔前叶等部分脑区。另一条主线探讨广泛的元认知功能与广泛大脑网络的相关。研究提出了大脑的“元认知网络”的概念,发现脑损伤或病变造成的元认知功能损伤与脑功能网络有关,而非固定在某一特定脑区。建议未来的研究应重视四个方面的研究:元认知加工的具体脑区和脑功能网络,元认知神经机制的分离,元认知脑功能的损伤和元认知训练的改善作用,以及基于神经机制研究的元认知模型的建构与修正。     

儿童早期精细动作技能与认知发展的关系

精细动作技能指个体主要凭借手以及手指等部位的小肌肉或小肌肉群而产生的运动, 它可以为个体提供认知经验, 丰富认知对象, 进而促进个体对事物本质的认识。当个体需要将认知资源-注意在两个或多个任务之间进行分配时, 熟练的精细动作可以节省注意资源, 为高级的认知任务更好地服务; 精细动作与认知在发展中不断相互促进, 有些动作是某些认知习得或认知练习的先决条件; 精细动作技能可以预测小学低年级的学业成绩, 尤其是阅读和数学成绩。精细动作技能和认知发展的关系具有大脑神经发育基础, 它们在某种程度上共享相同的脑区, 如小脑和前额叶。因此, 某些认知损伤的病症可以通过精细动作的训练而得到改善和治疗。     

内侧前额叶皮质—— “自我”的神经基础

自我神经基础的探讨常基于自我相关加工的研究, 涉及皮质中线结构各个脑区甚至全脑协同作用。内侧前额叶皮质及其次成分在自我相关加工中发挥重要作用：腹内侧前额叶皮质较多支持默认模式下的自我加工、自我信息的觉察和“在线”自我加工, 背内侧前额叶皮质主要参与有意识的自我参照加工、自我信息的评价和“主导的”自我加工。在自我-他人表征中, 自我-他人表征的情感性、认知性和文化性因素均调节内侧前额叶皮质及次成分的活动。未来在动态的时间和人际背景中解析自我加工的神经机制是重要的研究方向。     

人际互动中社会学习的计算神经机制

人类在社会互动中通过他人的行为对他人特质、意图及特定情境下的社会规范进行学习, 是优化决策、维护积极社会互动的重要条件。近年来, 越来越多的研究通过结合计算模型与神经影像技术对社会学习的认知计算机制及其神经基础进行了深入考察。已有研究发现, 人类的社会学习过程能够较好地被强化学习模型与贝叶斯模型刻画, 主要涉及的认知计算过程包括主观期望、预期误差和不确定性的表征以及信息整合的过程。大脑对这些计算过程的执行主要涉及奖惩加工相关脑区(如腹侧纹状体与腹内侧前额叶)、社会认知加工相关脑区(如背内侧前额叶和颞顶联合区)及认知控制相关脑区(如背外侧前额叶)。需要指出的是, 计算过程与大脑区域之间并不是一一映射的关系, 提示未来研究可借助多变量分析与脑网络分析等技术从系统神经科学的角度来考察大尺度脑网络如何执行不同计算过程。此外, 将来研究应注重生态效度, 利用超扫描技术考察真实互动下的社会学习过程, 并更多地关注内隐社会学习的计算与神经机制。     

孤独症儿童动作发展障碍的神经机制

动作发展障碍(Developmental motor disorders)是孤独症谱系障碍的常见特征。通过系统回顾孤独症儿童动作发展障碍的神经科学研究, 发现γ-氨基丁酸和5-羟色胺浓度的改变及γ-氨基丁酸相关蛋白和Shank蛋白的表达异常不仅会损害中枢神经系统的发育, 而且还能导致突触兴奋性与抑制性失衡, 进而改变孤独症儿童小脑和大脑皮层运动区的功能连接。孤独症儿童小脑、基底神经节和胼胝体结构的改变对全脑的连通性产生了负面影响。神经生化机制和脑结构的异常共同导致了脑功能的异常, 最终造成孤独症儿童的动作发展障碍。此外, 动作发展障碍与孤独症核心症状共同的神经基础主要包括镜像神经元系统紊乱, 丘脑、基底神经节和小脑异常以及SLC7A5和PTEN 基因突变。未来研究需要关注与运动密切相关的其他神经递质, 如乙酰胆碱和多巴胺; 探索动作发展障碍神经网络的动态机制及其形成; 剖析该障碍的神经机制和自闭症核心症状神经机制的相互作用。     

计算的脑机制研究进展

采用计算任务来探讨脑机制已成为国外研究大脑活动的重要领域。该文阐述了神经心理学和脑成像领域有关计算的脑机制研究。神经心理学及脑损伤的研究结果表明,大脑两侧顶下小叶和左前额叶与计算加工有关。ERP、PET和fMRI脑成像研究结果显示,数字命名与比较、心算、精算和估算等不同计算任务,其所激活的脑部位有所差异,但是大脑两侧顶下小叶和左前额叶可能是计算加工的主要脑部位。由于研究材料、方法和程序的不同,大脑皮层的广泛区域都有可能参与计算加工。     

Duration judgments in children with ADHD suggest deficient utilization of temporal information rather than general impairment in timing.

Clinicians, parents, and teachers alike have noted that individuals with ADHD often have difficulties with "time management," which has led some to suggest a primary deficit in time perception in ADHD. Previous studies have implicated the basal ganglia, cerebellum, and frontal lobes in time estimation and production, with each region purported to make different contributions to the processing and utilization of temporal information. Given the observed involvement of the frontal-subcortical networks in ADHD, we examined judgment of durations in children with ADHD (N = 27) and age- and gender-matched control subjects (N = 15). Two judgment tasks were administered: short duration (550 ms) and long duration (4 s). The two groups did not differ significantly in their judgments of short interval durations; however, subjects with ADHD performed more poorly when making judgments involving long intervals. The groups also did not differ on a judgment-of-pitch task, ruling out a generalized deficit in auditory discrimination. Selective impairment in making judgments involving long intervals is consistent with performance by patients with frontal lobe lesions and suggests that there is a deficiency in the utilization of temporal information in ADHD (possibly secondary to deficits in working memory and/or strategy utilization), rather than a problem involving a central timing mechanism.     

Processing emotional tone from speech in Parkinson’s disease: A role for the basal ganglia

In this study, individuals with Parkinson's disease were tested as a model for basal ganglia dysfunction to infer how these structures contribute to the processing of emotional speech tone (emotional prosody). Nondemented individuals with and without Parkinson's disease (n = 21/group) completed neuropsychological tests and tasks that required them to process the meaning of emotional prosody in various ways (discrimination, identification, emotional feature rating). Individuals with basal ganglia disease exhibited abnormally reduced sensitivity to the emotional significance of prosody in a range of contexts, a deficit that could not be attributed to changes in mood, emotional-symbolic processing, or estimated frontal lobe cognitive resource limitations in most conditions. On the basis of these and broader findings in the literature, it is argued that the basal ganglia provide a critical mechanism for reinforcing the behavioral significance of prosodic patterns and other temporal representations derived from cue sequences (Lieberman, 2000), facilitating cortical elaboration of these events.     

Neurological basis of language and sequential cognition: evidence from simulation,aphasia, and ERP studies

The current research addresses the hypothesis that certain aspects of sequential cognition have made substantial contributions to the human language processing capability, from a functional neurophysiology perspective. We first describe a cognitive sequence processing model that was developed based on the functional neuroanatomy of primate cortex and basal ganglia. We demonstrate how this model is capable of simulating the behavior of human infants in extracting serial, temporal and abstract structure from language-like sound sequences as revealed in recent psycholinguistic experiments. We then demonstrate how, through training, this model can perform adult level syntactic comprehension, based on dissociated processing streams for open vs. closed class words. The model subsequently predicts: (1) that impaired syntactic processing (as in agrammatic aphasia) will be associated with impairments in corresponding non-linguistic cognitive sequencing tasks, and (2) that neurophysiological processes (as revealed by ERPs) involved in syntactic processing should also be involved in the corresponding non-linguistic cognitive sequencing tasks. Data confirming these predictions are reviewed. We conclude that the study of sequential cognition will provide a new paradigm for the investigation of the neurophysiological bases of language.     

Adaptive neural models of queuing and timing in fluent action

In biological cognition, specialized representations and associated control processes solve the temporal problems inherent in skilled action. Recent data and neural circuit models highlight three distinct levels of temporal structure: sequence preparation, velocity scaling, and state-sensitive timing. Short sequences of actions are prepared collectively in prefrontal cortex, then queued for performance by a cyclic competitive process that operates on a parallel analog representation. Successful acts like ball-catching depend on coordinated scaling of effector velocities, and velocity scaling, mediated by the basal ganglia, may be coupled to perceived time-to-contact. Making acts accurate at high speeds requires state-sensitive and precisely timed activations of muscle forces in patterns that accelerate and decelerate the effectors. The cerebellum may provide a maximally efficient representational basis for learning to generate such timed activation patterns.     

Basal ganglia, dopamine and temporal processing: performance on three timing tasks on and off medication in Parkinson's disease

A pervasive hypothesis in the timing literature is that temporal processing in the milliseconds and seconds range engages the basal ganglia and is modulated by dopamine. This hypothesis was investigated by testing 12 patients with Parkinson's disease (PD), both 'on' and 'off' dopaminergic medication, and 20 healthy controls on three timing tasks. In a seconds range (30-120 s) time production task, patients tested 'on' medication showed a significantly different accuracy profile compared to controls and when tested 'off' medication. However, no group or on vs off medication differences in accuracy were found on a time reproduction task and a warned reaction time task requiring temporal processing within the 250-2000 ms range. Variability was measured using the coefficient of variation, with the performance of the patient group on the time reproduction task violating the scalar property, suggesting atypical temporal processing mechanisms. The data suggest that the integrity of the basal ganglia is necessary for 'typical' time production in the seconds range as well as for time reproduction at shorter intervals. Exploratory factor analysis suggested that the time production task uses neural mechanisms distinct from those used in the other two timing tasks. The dissociation of the effects of dopaminergic medication and nature of task on performance in PD raises interesting questions about the pharmacological mediation and task-specificity of deficits in temporal processing.     

Clock drawing performance and brain morphology in mild cognitive impairment and Alzheimer's disease

The Clock Drawing Test (CDT) is a widely used instrument in the neuropsychological assessment of Alzheimer's disease (AD). As CDT performance necessitates several cognitive functions (e.g., visuospatial and constructional abilities, executive functioning), an interaction of multiple brain regions is likely. Fifty-one subjects with mild cognitive impairment, 23 with AD and 15 healthy controls underwent high-resolution magnetic resonance imaging. Optimized voxel-based morphometry (VBM) was performed to investigate the putative association between CDT performance and gray matter (GM) density throughout the entire brain. In the first step of analysis (p<.001, uncorrected), VBM revealed a reduced GM density in numerous cortical (temporal lobe, frontal lobe, parietal lobe, cerebellum) and subcortical (thalamus, basal ganglia) brain regions to be associated with poorer CDT performance. When corrected for multiple comparisons (p<.01), the associations remained significant predominantly in the left temporal and--less pronounced--the right temporal lobe. VBM demonstrated CDT performance to depend on the integrity of widely distributed cortical and subcortical areas in both brain hemispheres with accentuation in the left-sided temporal lobe region.     

Effects of focal basal ganglia lesions on timing and force control

Studies of basal ganglia dysfunction in humans have generally involved patients with degenerative disorders, notably Parkinson's disease. In many instances, the performance of these patients is compared to that of patients with focal lesions of other brain structures such as the cerebellum. In the present report, we studied the performance of patients with focal basal ganglia lesions on three fundamental motor tasks. The patients all had suffered unilateral damage in the striatum and were tested in the chronic state. The first task required the participants to tap with their index finger as fast as possible; this test provided a simple assessment of motor competence. Compared to controls, the maximum tapping rate was lower for the patients when tapping with their contralesional limb, although the deficit was not severe. The second and third tasks were designed to assess timing and force control, two functions that have been associated with basal ganglia function. The patients performed similar to controls on both tasks and showed no evidence of impairment when using their contralesional limb compared to their ipsilesional limb. The results indicate that unilateral basal ganglia lesions tend to produce minor motor problems in force control, and fail to support the hypothesized role of the basal ganglia in timing.