Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94304, United States.
Neuroimage. 2018 Oct 15;180(Pt B):505-514. doi: 10.1016/j.neuroimage.2017.07.001. Epub 2017 Jul 3.
The neuroscience of mind-wandering has begun to flourish, with roles of brain regions and networks being defined for various components of spontaneous thought. However, most of brain activity does not represent immediately occurring thoughts. Instead, spontaneous, organized network activity largely reflects "intrinsic" functions that are unrelated to the current experience. There remains no consensus on how brain networks represent mind-wandering in parallel to functioning in other ongoing, predominantly unconscious processes. Commonly, in network analysis of functional neuroimaging data, functional connectivity (FC; correlated time series) between remote brain regions is considered over several minutes or longer. In contrast, dynamic functional connectivity (dFC) is a new, promising approach to characterizing spontaneous changes in neural network communication on the faster time-scale at which intra-individual fluctuations in thought contents may occur. Here I describe how a potential relationship between mind-wandering and FC has traditionally been considered in the literature, and I review methods and results pertaining to the study of the dFC-mind-wandering relationship. While acknowledging challenges to the dFC approach and to behaviorally capturing fluctuations in inner experiences, I describe a framework for describing spontaneous thoughts in terms of brain-network activity patterns that are comprised of connections weighted by time-varying relevance to conscious and unconscious processing. This perspective suggests preferential roles of certain anatomical communication avenues (e.g., via the default mode network) in mind-wandering, while also implying that a region's connectivity fluctuates over time in its immediate degree of relevance to conscious contents, ultimately allowing novelty and diversity of thought.
意识流的神经科学研究已经开始蓬勃发展，大脑区域和网络的作用被定义为自发思维的各种组成部分。然而，大多数大脑活动并不代表当前发生的想法。相反，自发的、有组织的网络活动在很大程度上反映了与当前经验无关的“内在”功能。目前还没有达成共识，即大脑网络如何在与其他正在进行的、主要是无意识的过程并行的情况下代表意识流。通常，在功能神经影像学数据的网络分析中，远程脑区之间的功能连接（FC；相关时间序列）被认为是在几分钟或更长时间内。相比之下，动态功能连接（dFC）是一种新的、有前途的方法，可以在思想内容个体内波动可能发生的更快时间尺度上，描述神经网络通信的自发变化。在这里，我描述了文献中传统上如何考虑意识流和 FC 之间的潜在关系，并回顾了与研究 dFC-意识流关系相关的方法和结果。在承认 dFC 方法和行为捕捉内在体验波动的挑战的同时，我描述了一种根据包含由与意识和无意识处理的时变相关性加权的连接的脑网络活动模式来描述自发思维的框架。这种观点表明，某些解剖学沟通途径（例如，通过默认模式网络）在意识流中具有优先作用，同时也意味着一个区域的连通性随时间变化，与其对意识内容的直接相关性，最终允许思维的新颖性和多样性。
