Computational, Cognitive, and Clinical Neuroimaging Laboratory, Division of Brain Sciences, Faculty of Medicine, Imperial College London, Hammersmith Hospital Campus, London W12 0NN, United Kingdom, and Department of Computing, Imperial College London, London SW7 2RH, United Kingdom.
J Neurosci. 2014 Jan 8;34(2):451-61. doi: 10.1523/JNEUROSCI.1853-13.2014.
Understanding how dynamic changes in brain activity control behavior is a major challenge of cognitive neuroscience. Here, we consider the brain as a complex dynamic system and define two measures of brain dynamics: the synchrony of brain activity, measured by the spatial coherence of the BOLD signal across regions of the brain; and metastability, which we define as the extent to which synchrony varies over time. We investigate the relationship among brain network activity, metastability, and cognitive state in humans, testing the hypothesis that global metastability is "tuned" by network interactions. We study the following two conditions: (1) an attentionally demanding choice reaction time task (CRT); and (2) an unconstrained "rest" state. Functional MRI demonstrated increased synchrony, and decreased metastability was associated with increased activity within the frontoparietal control/dorsal attention network (FPCN/DAN) activity and decreased default mode network (DMN) activity during the CRT compared with rest. Using a computational model of neural dynamics that is constrained by white matter structure to test whether simulated changes in FPCN/DAN and DMN activity produce similar effects, we demonstate that activation of the FPCN/DAN increases global synchrony and decreases metastability. DMN activation had the opposite effects. These results suggest that the balance of activity in the FPCN/DAN and DMN might control global metastability, providing a mechanistic explanation of how attentional state is shifted between an unfocused/exploratory mode characterized by high metastability, and a focused/constrained mode characterized by low metastability.
理解大脑活动的动态变化如何控制行为是认知神经科学的主要挑战。在这里，我们将大脑视为一个复杂的动态系统，并定义了两种大脑动力学的度量：大脑活动的同步性，通过大脑区域之间的 BOLD 信号的空间相干性来测量；以及亚稳性，我们将其定义为同步性随时间变化的程度。我们研究了人类大脑网络活动、亚稳性和认知状态之间的关系，检验了全局亚稳性是通过网络相互作用“调谐”的假设。我们研究了以下两种情况：（1）注意力要求高的选择反应时任务（CRT）；（2）不受约束的“休息”状态。功能磁共振成像显示，与休息相比，CRT 期间前额顶叶控制/背侧注意网络（FPCN/DAN）活动的同步性增加，默认模式网络（DMN）活动的亚稳性降低。使用受白质结构约束的神经动力学计算模型来测试 FPCN/DAN 和 DMN 活动的模拟变化是否产生相似的效果，我们证明了 FPCN/DAN 的激活增加了全局同步性并降低了亚稳性。DMN 的激活则产生相反的效果。这些结果表明，FPCN/DAN 和 DMN 的活动平衡可能控制全局亚稳性，为注意力状态如何在以高亚稳性为特征的无焦点/探索模式和以低亚稳性为特征的聚焦/约束模式之间切换提供了一种机制解释。
