Visscher Kristina M, Miezin Francis M, Kelly James E, Buckner Randy L, Donaldson David I, McAvoy Mark P, Bhalodia Vidya M, Petersen Steven E
Department of Neurology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA.
Neuroimage. 2003 Aug;19(4):1694-708. doi: 10.1016/s1053-8119(03)00178-2.
Recent functional magnetic resonance imaging (fMRI) studies using mixed blocked/event-related designs have shown activity consistent with separable sustained task-related processes and transient trial-related processes. In the mixed design, control blocks are intermixed with task blocks, during which trials are presented at varying intervals. Two studies were conducted to assess the ability of this design to detect and dissociate sustained task-related from transient trial-related activity. Analyses on both simulated and empirical data were performed by using the general linear model with a shape assumed for sustained effects, but not transient effects. In the first study, simulated data were produced with sustained time courses, transient time courses, and the sum of both together. Analyses of these data showed appropriate parsing of sustained and transient activity in all three cases. For the empirical fMRI experiment, counterphase-flickering checkerboard stimuli were constructed to produce sustained, transient, and combined sustained and transient responses in visual cortex. As with the simulation, appropriate parsing of sustained and transient activity was seen in all three cases; i.e., sustained stimuli produced sustained time courses and transient stimuli produced transient time courses. Combined stimuli produced both transient and sustained time courses. Critically, transient stimuli alone did not produce spurious positive sustained responses; sustained stimuli alone produced negligible spurious transient time courses. The results of these two studies along with supplemental simulations provide strong evidence that mixed designs are an effective tool for separating transient, trial-related activity from sustained activity in fMRI experiments. Mixed designs can allow researchers a means to examine brain activity associated with sustained processes, potentially related to task-level control signals.
最近使用混合组块/事件相关设计的功能磁共振成像（fMRI）研究表明，其活动与可分离的持续任务相关过程和瞬态试验相关过程一致。在混合设计中，对照组块与任务组块相互混合，在此期间以不同的时间间隔呈现试验。进行了两项研究，以评估这种设计在检测和区分持续任务相关活动与瞬态试验相关活动方面的能力。通过使用一般线性模型对模拟数据和实证数据进行分析，该模型假设了持续效应的形状，但未假设瞬态效应的形状。在第一项研究中，生成了具有持续时间进程、瞬态时间进程以及两者之和的模拟数据。对这些数据的分析表明，在所有三种情况下都能对持续活动和瞬态活动进行适当的解析。对于实证fMRI实验，构建了反相闪烁棋盘格刺激，以在视觉皮层中产生持续、瞬态以及持续与瞬态相结合的反应。与模拟情况一样，在所有三种情况下都能看到对持续活动和瞬态活动的适当解析；即，持续刺激产生持续时间进程，瞬态刺激产生瞬态时间进程。组合刺激产生瞬态和持续时间进程。至关重要的是，单独的瞬态刺激不会产生虚假的正向持续反应；单独的持续刺激产生的虚假瞬态时间进程可以忽略不计。这两项研究的结果以及补充模拟提供了强有力的证据，表明混合设计是在fMRI实验中将瞬态、试验相关活动与持续活动分离的有效工具。混合设计可以为研究人员提供一种手段，来检查与持续过程相关的大脑活动，这些过程可能与任务水平控制信号有关。
