Massachusetts General Hospital Nuclear Magnetic Resonance Center and the Department of Radiology, Harvard Medical School, Boston, Massachusetts 02129, USA.
Hum Brain Mapp. 1997;5(5):329-40. doi: 10.1002/(SICI)1097-0193(1997)5:5<329::AID-HBM1>3.0.CO;2-5.
A major limitation in conducting functional neuroimaging studies, particularly for cognitive experiments, has been the use of blocked task paradigms. Here we explored whether selective averaging techniques similar to those applied in event-related potential (ERP) experiments could be used to demonstrate functional magnetic resonance imaging (fMRI) responses to rapidly intermixed trials. In the first two experiments, we observed that for 1-sec trials of full-field visual checkerboard stimulation, the fMRI blood oxygenation level-dependent (BOLD) signal summated in a roughly linear fashion across successive trials even at very short (2 sec and 5 sec) intertrial intervals, although subtle departures from linearity were observed. In experiments 3 and 4, we observed that it is possible to obtain robust activation maps for rapidly presented randomly mixed trial types (left- and right-hemifield visual checkerboard stimulation) spaced as little as 2 sec apart. Taken collectively, these results suggest that selective averaging may enable fMRI experimental designs identical to those used in typical behavioral and ERP studies. The ability to analyze closely spaced single-trial, or event-related, signals provides for a class of experiments which cannot be conducted using blocked designs. Trial types can be randomly intermixed, and selective averaging based upon trial type and/or subject performance is possible.
在进行功能神经影像学研究，特别是认知实验时，一个主要的限制因素一直是使用块状任务范式。在这里，我们探讨了是否可以使用类似于事件相关电位 (ERP) 实验中应用的选择性平均技术来证明快速混合试验的功能磁共振成像 (fMRI) 反应。在前两个实验中，我们观察到，对于全视野视觉棋盘刺激的 1 秒试验，即使在非常短的（2 秒和 5 秒）试验间间隔下，fMRI 血氧水平依赖 (BOLD) 信号也会以大致线性的方式在连续试验中累加，尽管观察到了细微的线性偏离。在实验 3 和 4 中，我们观察到，对于快速呈现的随机混合试验类型（左、右视野视觉棋盘刺激），间隔时间短至 2 秒，就有可能获得稳健的激活图。总的来说，这些结果表明，选择性平均可能使 fMRI 实验设计与典型的行为和 ERP 研究中使用的设计相同。分析紧密间隔的单次试验或事件相关信号的能力提供了一类无法使用块状设计进行的实验。试验类型可以随机混合，并且可以基于试验类型和/或受试者表现进行选择性平均。
