Laboratory of Behavioral & Cognitive Neuroscience, Stanford Human Intracranial Cognitive Electrophysiology Program, Department of Neurology & Neurological Sciences, Stanford University, Stanford, CA 94305
Proc Natl Acad Sci U S A. 2018 May 1;115(18):4785-4790. doi: 10.1073/pnas.1721714115. Epub 2018 Apr 16.
Neuroimaging evidence supports a role of the default mode network (DMN) in spontaneous thought and goal-driven internally oriented processes, such as recalling an autobiographical event, and has demonstrated its deactivation during focused, externally oriented attention. Recent work suggests that the DMN is not a homogeneous network but rather is composed of at least several subnetworks, which are engaged in distinct functions; however, it is still unclear if these different functions rely on the same neuronal populations. In this study, we used intracranial EEG to record from the posteromedial cortex (PMC), a core hub of the DMN, in 13 human subjects, during autobiographical memory retrieval (internally oriented), arithmetic processing (externally oriented), and cued rest (spontaneous thought), allowing us to measure activity from anatomically precise PMC sites with high temporal resolution. We observed a heterogeneous, yet spatially organized, pattern of activity across tasks. Many sites, primarily in the more ventral portion of PMC, were engaged during autobiographical recall and suppressed during arithmetic processing. Other more dorsal PMC sites were engaged during the cued-rest condition. Of these rest-active sites, some exhibited variable temporal dynamics across trials, possibly reflecting various forms of spontaneous thought, while others showed only transient activity at the beginning of cued-rest trials (i.e., after a switch from a task to cued rest), possibly involved in shifting the brain from a more focused to a more exploratory attentional state. These results suggest heterogeneity of function even within an individual node of the DMN.
神经影像学证据支持默认模式网络（DMN）在自发思维和目标导向的内部定向过程中的作用，例如回忆自传事件，并已证明其在专注于外部定向的注意力过程中失活。最近的工作表明，DMN 不是一个同质的网络，而是由至少几个子网组成，这些子网执行不同的功能；然而，目前尚不清楚这些不同的功能是否依赖于相同的神经元群体。在这项研究中，我们使用颅内 EEG 在 13 名人类受试者的后内侧皮层（PMC）记录，PMC 是 DMN 的核心枢纽，在自传体记忆检索（内部定向）、算术处理（外部定向）和提示休息（自发思维）期间，使我们能够以高时间分辨率测量来自解剖精确的 PMC 位置的活动。我们观察到跨任务的活动呈现出一种异构但空间组织的模式。许多部位主要位于 PMC 的更腹侧部分，在自传体回忆时活跃，在算术处理时被抑制。PMC 的其他更背侧部位在提示休息状态下活跃。在这些休息时活跃的部位中，有些在整个试验中表现出不同的时间动态，可能反映了各种形式的自发思维，而其他部位只在提示休息试验开始时表现出短暂的活动（即，在从任务切换到提示休息后），可能涉及将大脑从更专注的状态转变为更具探索性的注意力状态。这些结果表明，即使在 DMN 的单个节点内，功能也存在异质性。
