Burock M A, Buckner R L, Woldorff M G, Rosen B R, Dale A M
Massachusetts General Hospital, Nuclear Magnetic Resonance Center, Charlestown 02129, USA.
Neuroreport. 1998 Nov 16;9(16):3735-9. doi: 10.1097/00001756-199811160-00030.
Previous studies have shown that hemodynamic response overlap severely limits the maximum presentation rate with event-related functional MRI (fMRI) using fixed intertrial experimental designs. Here we demonstrate that the use of randomized experimental designs can largely overcome this limitation, thereby allowing for event-related fMRI experiments with extremely rapid presentation rates. In the first experiment, fMRI time courses were simulated using a fixed intertrial interval design with intervals of 16, 3, and 1 s, and using a randomized design having the same mean intertrial intervals. We found that using fixed intertrial interval designs the transient information decreased with decreasing intertrial intervals, whereas using randomized designs the transient information increased with decreasing mean intertrial intervals. In a second experiment, fMRI data were collected from two subjects using a randomized paradigm with visual hemifield stimuli presented randomly every 500 ms. Robust event-related activation maps and hemodynamic response estimates were obtained. These results demonstrate the feasibility of performing event-related fMRI experiments with rapid, randomized paradigms identical to those used in electrophysiological and behavioral studies, thereby expanding the applicability of event-related fMRI to a whole new range of cognitive neurosciences questions and paradigms.
以往的研究表明，血流动力学反应重叠严重限制了使用固定试验间隔实验设计的事件相关功能磁共振成像（fMRI）的最大呈现速率。在此我们证明，使用随机实验设计可以很大程度上克服这一限制，从而允许进行具有极快速呈现速率的事件相关fMRI实验。在第一个实验中，使用间隔为16、3和1秒的固定试验间隔设计以及具有相同平均试验间隔的随机设计来模拟fMRI时间进程。我们发现，使用固定试验间隔设计时，瞬态信息随着试验间隔的减小而减少，而使用随机设计时，瞬态信息随着平均试验间隔的减小而增加。在第二个实验中，使用随机范式从两名受试者收集fMRI数据，视觉半视野刺激每500毫秒随机呈现一次。获得了稳健的事件相关激活图和血流动力学反应估计值。这些结果证明了使用与电生理和行为研究中相同的快速、随机范式进行事件相关fMRI实验的可行性，从而将事件相关fMRI的适用性扩展到全新的一系列认知神经科学问题和范式。
