Department of Psychology and Center for Brain Science, Harvard University, Cambridge, Massachusetts, USA.
J Neurophysiol. 2010 Jul;104(1):322-35. doi: 10.1152/jn.00830.2009. Epub 2010 May 12.
A set of brain regions known as the default network increases its activity when focus on the external world is relaxed. During such moments, participants change their focus of external attention and engage in spontaneous cognitive processes including remembering the past and imagining the future. However, the functional contributions of the default network to shifts in external attention versus internal mentation have been difficult to disentangle because the two processes are correlated under typical circumstances. To address this issue, the present study manipulated factors that promote spontaneous cognition separately from those that change the scope of external attention. Results revealed that the default network increased its activity when spontaneous cognition was maximized but not when participants increased their attention to unpredictable foveal or peripheral stimuli. To examine the nature of participants' spontaneous thoughts, a second experiment used self-report questionnaires to quantify spontaneous thoughts during extended fixation epochs. Thoughts about one's personal past and future comprised a major focus of spontaneous cognition with considerable variability. Activity correlations between the medial temporal lobe and distributed cortical regions within the default network predicted a small, but significant, portion of the observed variability. Collectively, these results suggest that during passive states, activity within the default network reflects spontaneous, internally directed cognitive processes.
当专注于外部世界的注意力放松时，一组被称为默认网络的大脑区域会增加其活动。在这些时刻，参与者改变对外界注意力的焦点，并参与自发的认知过程，包括回忆过去和想象未来。然而，由于在典型情况下，这两个过程是相关的，因此默认网络对外部注意力与内部思维转变的功能贡献一直难以区分。为了解决这个问题，本研究分别操纵促进自发认知和改变外部注意力范围的因素。结果表明，当自发认知最大化时，默认网络会增加其活动，但当参与者增加对不可预测的中央凹或周边刺激的注意力时则不会。为了研究参与者自发思维的本质，第二项实验使用自我报告问卷来量化在延长注视时段期间的自发思维。关于个人过去和未来的想法是自发认知的主要关注点，具有相当大的可变性。内侧颞叶与默认网络内分布式皮质区域之间的活动相关性预测了观察到的可变性的一小部分，但具有统计学意义。总的来说，这些结果表明，在被动状态下，默认网络内的活动反映了自发的、内部导向的认知过程。
