Gaab Nadine, Gabrieli John D E, Glover Gary H
Developmental Medicine Center, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02215-5365, USA.
Hum Brain Mapp. 2008 Jul;29(7):858-67. doi: 10.1002/hbm.20578.
Studies have identified specific brain regions that increase activation during rest relative to attention-demanding tasks; these regions subserve the "default mode of brain function". Most of these studies have been conducted in the presence of scanner background noise (SBN). This noise has been shown to lead to altered attentional demands, and thus may modulate the default-mode network. Twelve subjects were examined during a rest condition that was contrasted with an auditory task. Words were presented either with SBN employing a conventional acquisition or without SBN using a sparse sampling approach. The number of experimental and resting trials was equated between the designs. Selecting the images in the condition with SBN that corresponded in time with the images in the condition without SBN made a direct comparison of the default-mode network (rest contrasted with active task) possible. There was typical activation of the default-mode network during rest versus task for both designs. However, SBN suppressed major components of the default-mode network, including medial prefrontal cortex, posterior cingulate, and precuneus. Our results suggest that the default mode of brain function differs when assessed in the presence compared to the absence of scanner noise, with the presence of scanner noise perhaps adding attentional demands that diminish activation changes between rest and task in a nonlinear way within the default network. Further studies are needed to clarify whether the use of a sparse sampling technique might enhance clinical utilities that have been proposed for analysis of the default-mode network.
研究已经确定了特定的脑区，这些脑区在静息状态下相对于需要注意力的任务会增加激活；这些区域支持“大脑功能的默认模式”。大多数这些研究是在存在扫描仪背景噪声（SBN）的情况下进行的。已表明这种噪声会导致注意力需求的改变，因此可能会调节默认模式网络。在与听觉任务形成对比的静息状态下对12名受试者进行了检查。单词呈现时，一种设计采用常规采集方式并伴有SBN，另一种设计采用稀疏采样方法且无SBN。两种设计中实验和静息试验的次数相等。选择有SBN条件下与无SBN条件下时间上相对应的图像，使得对默认模式网络（静息与主动任务对比）进行直接比较成为可能。两种设计在静息与任务状态下均出现了默认模式网络的典型激活。然而，SBN抑制了默认模式网络的主要组成部分，包括内侧前额叶皮质、后扣带回和楔前叶。我们的结果表明，与不存在扫描仪噪声相比，在存在扫描仪噪声的情况下评估大脑功能的默认模式时会有所不同，扫描仪噪声的存在可能增加了注意力需求，从而以非线性方式减少了默认网络中静息与任务之间的激活变化。需要进一步研究来阐明使用稀疏采样技术是否可能增强已提出的用于默认模式网络分析的临床效用。
