Fassbender Catherine, Zhang Hao, Buzy Wendy M, Cortes Carlos R, Mizuiri Danielle, Beckett Laurel, Schweitzer Julie B
M.I.N.D. Institute, Department of Psychiatry and Behavioral Sciences, University of California Davis Medical School, 2825 50th St., Sacramento, CA 95817, USA.
Brain Res. 2009 Jun 1;1273:114-28. doi: 10.1016/j.brainres.2009.02.070. Epub 2009 Mar 10.
Heightened distractibility in participants with ADHD as indexed by increased reaction time (RT) variability has been hypothesized to be due to a failure to sufficiently suppress activation in the default attention network during cognitively demanding situations. The present study utilized fMRI to examine the relationship between intra-individual variability (IIV) in task RT and suppression of BOLD response in regions of the default network, using a working memory paradigm and two levels of control tasks. IIV was calculated separately for thirteen healthy control and twelve children with ADHD, Combined Type. Children with ADHD displayed significantly more RT variability than controls. Neural measures showed that although both groups displayed a pattern of increasing deactivation of the medial prefrontal cortex (PFC) with increasing task difficulty, the ADHD group was significantly less deactive than controls. Correlations between IIV and brain activation suggested that greater variability was associated with a failure to deactivate ventromedial PFC with increasing task difficulty. T-tests on brain activation between participants with ADHD with low versus high IIV implicated a similar region so that high variability was associated with greater activity in this region. These data provide support for the theory that increased distractibility in at least some participants with ADHD may be due to an inability to sufficiently suppress activity in the default attention network in response to increasing task difficulty.
反应时间（RT）变异性增加表明患有注意力缺陷多动障碍（ADHD）的参与者注意力分散性增强，据推测，这是由于在认知要求较高的情况下，未能充分抑制默认注意力网络中的激活。本研究利用功能磁共振成像（fMRI），采用工作记忆范式和两个水平的控制任务，来检验任务RT的个体内变异性（IIV）与默认网络区域中血氧水平依赖（BOLD）反应抑制之间的关系。分别计算了13名健康对照者和12名混合型ADHD儿童的IIV。ADHD儿童的RT变异性显著高于对照组。神经测量结果显示，尽管两组均呈现出随着任务难度增加，内侧前额叶皮质（PFC）失活增加的模式，但ADHD组的失活程度明显低于对照组。IIV与脑激活之间的相关性表明，随着任务难度增加，更大的变异性与腹内侧PFC未能失活有关。对低IIV与高IIV的ADHD参与者之间的脑激活进行t检验，涉及一个类似区域，因此高变异性与该区域的更大活动有关。这些数据支持了这样一种理论，即至少部分ADHD参与者注意力分散性增加可能是由于在任务难度增加时，无法充分抑制默认注意力网络中的活动。
