交互式特异化理论是认知神经发育领域的重要理论，与以往强调脑区与认知功能一一对应的成熟观不同，它更强调大脑区域之间的协作性，这一理论的提出也让研究者们开始从脑网络的角度来研究认知发育背后的神经机制。而执行功能作为一项非常重要的认知能力，包括了抑制控制、工作记忆及认知灵活性等关键成分，涵盖了处理各种认知挑战所必需的过程，其背后的神经机制是认知神经发育领域一个备受关注的话题，目前也已经有了大量的研究积累，从以往仅强调前额叶区域单独作用的成熟论观点，到交互式特异化理论的转变，又进一步发现了额顶与默认网络这样大型脑网络的交互在执行功能发育的重要作用。但是近期出现的工作记忆动态编码的理论又提出，即使个体看似处于维持信息的稳定状态时，神经元活动也是在不断发生变化的，这也对我们产生了新的启发。交互式特异化理论指出了网络协作对认知发育的作用，而动态编码理论的提出也告诉我们从动态的角度来看待这种协作的重要性，额顶与默认网络在完成执行任务的时候，可能会短暂地变换连接与激活的模式以适应任务需求，这也被称之为动态重组的过程。而在儿童青少年期执行功能本身也经历着持续性的发展，其发育对于个体的适应能力、学业成就及心理健康等都有着巨大影响，执行功能的失调也与儿童青少年行为问题的出现息息相关，如焦虑、抑郁等内化问题，注意问题，当然也包括攻击行为、违反纪律等外化问题。而功能网络的动态活动近年来被认为可以更好地捕捉到认知任务中瞬时变化的信息，也能为一些精神与发育障碍类疾病提供新兴的预测与识别指标。那么在儿童青少年这一认知能力快速发展的时期，厘清执行功能下额顶与默认网络呈现出什么样的动态变换模式以及背后的结构特征。而以往认知神经科学发育领域的研究中也强调了，认知能力与大脑功能之间的关系也会在发育的过程中受到遗传与环境因素的影响，基因影响着大脑皮层的功能分布，而后天的经验也会塑造大脑的功能，尤其是一些负面事件的体验，家庭的贫困、父母的离异、学校的变动等事件都会给儿童青少年期的个体带来持续性的影响，因此，探究基因与环境因素对于额顶与默认网络动态重组活动的影响也是必要的。

为了回答这些问题，综合多模态的磁共振成像技术、动态系统切换模型、双生子研究设计等，我们通过三个研究，关注执行功能相关脑网络的动态切换在儿童青少年期对认知能力的关键作用，并进一步探寻影响这种功能动态变换的结构基础、遗传与环境因素。首先，在研究一中，我们考察了学龄儿童在完成工作记忆任务时额顶网络与默认网络这两个关键网络的动态变换模式，并且与成人进行了对比；而这种功能动态变换的发育差异是否是由于结构基础的发育差异所导致的呢？在研究二中我们进行了探索。在厘清执行功能相关脑网络的动态活动可以促进认知能力发育的同时，我们也想知道这种动态活动是否可以反映与执行功能密切相关的行为问题的出现，并且有哪些因素在影响着这些动态活动呢？这便是我们研究三所想要回答的问题。

首先，在研究一中，我们利用一项新兴的基于贝叶斯定理与隐马尔可夫链的动态系统切换模型，研究了儿童与成人在完成具有不同认知需求的执行功能时，额顶网络与默认网络动态重组活动的不同模式。通过定义出额顶网络与默认网络在整个任务过程中的不同状态以及状态相应的动态特征，我们进一步刻画两个网络动态变换模式的发育差异，我们发现相较于成人而言，儿童具有更不成熟的动态变换模式，具体表现为更难切换和维持与高认知需求相关的有效大脑状态，而更容易切换到一种不活跃的与认知需求低相关的大脑状态，这种动态变换也可以介导额顶网络与默认网络静态连接的组织模式与行为表现之间的关系。

而执行功能相关的脑网络之所以出现这样动态变换模式的发育差异，则可能是由于大脑结构上的差异所导致的。在研究二中，我们进一步探讨支持执行功能发育的网络动态活动背后的大脑结构特征，利用弥散磁共振成像与纤维束追踪技术构建了额顶网络与默认网络的结构连接网络，发现两个网络的结构连接随着年龄的发育而增强，并且结构连接的增强伴随着功能网络更多的动态活动，尤其支持与行为表现相关的动态切换，同时我们还发现结构与静态功能连接之间的低耦合通常预示着更多与更灵活的动态活动。

在前面的研究中，我们发现了额顶网络与默认网络的动态重组活动可以促进认知能力的发育，而在研究三中，我们又进一步发现了减少的动态活动也与青少年期行为问题的出现密切相关，那么究竟是哪些因素在影响着这些功能网络的动态表现呢？我们利用双生子研究的设计发现了额顶网络与默认网络动态活动的遗传效应并不显著，而是受环境因素的影响更大，其中生活压力事件的发生可能会造成动态切换活动的减少。那么，环境与遗传对所有功能网络动态变换的影响是否都是一样呢？还是说存在脑区的特异性？我们也对生活压力与遗传因素对全脑其他网络动态活动进行了分析，根据功能网络的层级化的特点，我们发现像视觉与躯体运动网络这样单模态的低级感知觉脑区则是受遗传因素影响的程度明显高于额顶网络与默认网络这样跨模态的高级脑区，另外，皮层下区域的遗传度也较为显著，并且会受到与多巴胺系统密切相关的COMT基因的影响，这个结果证实了影响脑网络动态变换的遗传效应与环境效应的脑区特异性。

总之，本研究结合多模态的磁共振成像数据、动态系统切换模型、双生子研究设计以及基因数据等，发现了与成人相比，在儿童期，额顶与默认网络的动态重组模式表现出更难维持与切换到与高认知需求相关的状态，这可能是由于儿童大脑结构组织的不成熟所导致的，这也意味着，随着年龄的增长，结构连接的成熟会支持执行功能相关的脑网络会呈现出更为高效的动态活动模式，这有利于提升学龄儿童认知行为的表现。与此同时，我们也发现，额顶网络与默认网络动态活动的减少意味着青少年期更多行为问题的出现，这表明执行功能相关脑网络动态重组模式的发展不仅可以提升认知表现，也可以减少行为问题。而与执行功能相关的额顶网络与默认网络的动态重组模式受环境因素的影响更大，生活压力事件的多发可能会减少功能网络的动态变换，由此影响认知与行为的发育。

Interactive specialization theory is an important theory in the field of cognitive neuroscience development. In contrast to the maturational view that emphasizes the one-to-one mapping between brain regions and cognitive functions, this theory emphasizes the collaboration among brain regions. Its proposal has enabled researchers to begin studying the neural mechanisms behind cognitive development from the perspective of brain networks. Executive function, as a very important cognitive ability, includes key components such as inhibition control, working memory, and cognitive flexibility, covering the processes required to handle various cognitive challenges. Its neural mechanisms are a topic of great concern in the field of cognitive neuroscience development. With the shift from the maturational theory that emphasizes the independent role of the prefrontal cortex to the interactive specialization theory, the importance of the interaction between the large brain networks, including the frontoparietal and default mode networks, in the development of executive functions has been further discovered. However, the recently proposed theory of dynamic encoding of working memory suggests that even when an individual seems to be in a stable state of maintaining information, neuronal activity is constantly changing. This has given us new insights. The interactive specialization theory points out the role of network interactions in cognitive development, while the dynamic encoding theory tells us about the importance of investigating this interaction from a dynamic perspective. When performing executive tasks, the frontoparietal and default mode networks may temporarily change their connectivity and activation patterns to adapt to task demands. This is also known as the process of dynamical reconfiguration. During childhood and adolescence, executive functions are also undergoing continuous development, and their development has a huge impact on individuals' adaptation ability, academic achievement, and mental health. Dysfunction of executive functions is also closely related to behavioral problems in children and adolescents, such as internalizing problems like anxiety and depression, attention problems, as well as externalizing problems such as aggression and violation of rules. In recent years, the dynamic activity of functional networks has been considered to better capture the momentary changes in cognitive tasks, and can provide emerging predictive and identification indicators for some mental and developmental disorders. Therefore, in the period of rapid development of cognitive abilities, it is particularly important to clarify what dynamic reconfiguration patterns the frontoparietal and default mode networks exhibit when performing executive functions and what structural characteristics support this dynamic function. Previous studies in the field of developmental cognitive neuroscience have also emphasized that the relationship between cognitive abilities and brain function is influenced by genetic and environmental factors during development. Genes influence the functional distribution of the cerebral cortex, and postnatal experience can also shape brain function, especially negative events such as experience of poverty, parental divorce, and school changes, which all have lasting effects on individuals during childhood and adolescence. Therefore, it is necessary to explore the influence of both genetic and environmental factors on the dynamic reorganization of the frontoparietal and default mode networks.

To answer these questions, we used multimodal magnetic resonance imaging techniques, dynamic system switching models, and twin study designs to focus on the key role of dynamic reconfiguration of executive function-related brain networks in cognitive abilities during childhood and adolescence and further explore the structural basis, genetic and environmental factors that affect this dynamic functional reconfiguration. First, in Study 1, we examined the dynamic switching patterns of the frontoparietal and default mode networks, two key networks, in completing working memory tasks in school-aged children, and compared them with adults. Is the developmental difference in this dynamic functional configuration due to differences in structural development? We explored this in Study 2. While clarifying how the dynamic activity of executive function-related brain networks can promote the cognitive development, we also want to know whether this dynamic activity can reflect the emergence of behavioral problems closely related to executive functions and what factors are affecting these dynamic activities. This is the question that we want to answer in Study 3.

In Study 1, we used an emerging dynamic system switching model based on Bayesian theorem and hidden Markov chains to study the different patterns of dynamic reorganization activity of the frontoparietal and default mode networks in children and adults when completing executive functions with different cognitive demands. By defining the different states of the frontoparietal and default mode networks throughout the task process and their corresponding dynamic features, we further characterize the developmental differences in the dynamic switching patterns of the two networks. We found that compared to adults, children have more immature dynamic switching patterns, which manifest as difficulty in switching and maintaining effective brain states related to high cognitive demands, and a tendency to switch to an inactive brain state related to low cognitive demands. This dynamic configuration can also mediate the relationship between the organizational patterns of static connections between the frontoparietal and default mode networks and behavioral performance.

The developmental differences in the dynamic reconfiguration patterns of executive function-related brain networks may be caused by differences in brain structure. In Study 2, we further explored the brain structural characteristics underlying the dynamic network that supports the development of executive function. We constructed structural connectivity networks of the frontoparietal and default mode networks using diffusion magnetic resonance imaging and fiber tracking techniques. We found that the structural connections of both networks increased with age, and the strengthening of the structural connections was accompanied by more dynamic activity in the functional networks, particularly supporting dynamic switching related to behavioral performance. We also found that low coupling between the structural and static functional connections usually indicates more and more flexible dynamics.

In our previous studies, we found that the dynamic reconfiguration of the frontoparietal and default mode networks can promote cognitive development, while in Study 3, we further discovered that reduced dynamic activity is closely related to the emergence of behavioral problems in adolescence. So what factors are influencing the dynamics of these functional networks? We used a twin study design and found that the genetic effects on the dynamic activity of the frontoparietal and default mode networks are not significant, but are more influenced by environmental factors, with the occurrence of stressful life events possibly leading to a reduction in dynamic switching. Are the effects of environment and genetics on the dynamic reconfiguration of all functional networks the same, or is there a specificity in different brain regions? We also analyzed the effects of stressful events and genetic factors on the dynamics of other networks in the entire brain. According to the hierarchical nature of functional networks, we found that low-level perceptual brain regions, such as the visual and somatomotor networks, are more influenced by genetic factors than higher-level transmodal brain regions like the frontoparietal and default mode networks. In addition, genetic influences are more significant in subcortical regions and are affected by the COMT gene closely related to the dopamine system. These results confirm the regional specificity of genetic and environmental effects on brain network dynamic reconfiguration.

In summary, this study combines multimodal magnetic resonance imaging data, dynamic system switching models, twin study designs, and genetic data, and found that compared to adults, children exhibit more difficulty in maintaining and switching to states related to high cognitive demands in the dynamic reorganization patterns of the frontoparietal and default mode networks. This may be due to the immature organization of the brain structure in children, which also means that with age, the maturation of structural connections will support more efficient dynamic patterns in the brain networks related to executive function, which is conducive to improving cognitive and behavioral performance in school-aged children. At the same time, we also found that the reduction of dynamic in the frontoparietal and default mode networks during adolescence indicates the emergence of more behavioral problems. This demonstrates that the development of dynamic reconfiguration in the brain networks related to executive function can not only improve cognitive performance, but also reduce behavioral problems. Dynamic reconfiguration of the frontoparietal and default mode networks related to executive function are more affected by environmental factors, and frequent life stressful events may reduce the dynamic of functional networks, thereby affecting the development of cognition and behavior.