The ERP omitted stimulus response to "no-stim" events and its implications for fast-rate event-related fMRI designs
The ERP omitted stimulus response to "no-stim" events and its implications for fast-rate event-related fMRI designs
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DOI：
10.1016/s1053-8119(03)00012-0
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发表时间：
2003-04-01
期刊：
影响因子：
5.7
通讯作者：
Woldorff, MG
中科院分区：
文献类型：
--
作者：
Busse, L;Woldorff, MG
快速事件相关功能磁共振成像实验的一个主要困难是刺激序列中相邻试验的大量重叠。解决该问题的一种方法是将“无刺激”或“无效”事件作为试验类型。这些是随机的，就好像它们是真正的刺激事件，但实际上没有刺激发生。假设空事件没有引起响应，则它们的时间锁定平均值仅反映平均重叠。因此，将其他试验类型的平均值与空事件平均值进行对比减去了重叠，使得能够提取这些其他试验类型的响应函数。然而，ERP研究表明，内源性脑反应，省略的刺激反应（OSR），可以引起一个失踪的事件在一个流的定期发生的刺激。在事件相关的功能磁共振成像实验中，这种反应是由零事件引起的，零事件减法或对比会错误地将OSR的倒数引入到其他试验类型的平均反应中。使用高密度ERP记录，我们研究了不同百分比的遗漏刺激（11%，22%和33%）的听觉OSR在刺激率为每秒一个事件或每2秒一个事件。在1-s条件下以及在11%的2-s条件下，每个百分比都有显著的OSR。反应包括早期的后负波（180-280 ms），随后是较大的前正波。这些结果对快速功能磁共振成像设计具有重要意义，同时也为大脑对遗漏刺激的反应提供了新的数据。(C)2003 Elsevier Science（美国）。All rights reserved.
A major difficulty in fast-rate event-related fMRI experiments is the extensive overlap from adjacent trials in the stimulus sequence. One approach to address this problem is to include "no-stim" or "null" events as a trial type. These are randomized as if they were true stimulus events but no stimulus actually occurs. Assuming that no response is elicited by the null events, their time-locked average reflects only the averaged overlap. Thus, contrasting the averages for the other trial types versus the null-event average subtracts out the overlap, enabling the extraction of the response functions for these other trial types. ERP studies, however, have indicated that an endogenous brain response, the omitted stimulus response (OSR), can be evoked by a missing event in a stream of regularly occurring stimuli. To the extent that this response is elicited by null events in an event-related fMRI experiment, the null-event subtraction or contrast would falsely introduce the inverse of the OSR into the averaged responses to the other trial types. Using high-density ERP recordings, we investigated the effect of different percentages of omitted stimuli (11, 22, and 33%) on the auditory OSR at stimulus rates of one event per second or one event per 2 s. Significant OSRs were found for each percentage in the 1-s condition as well as in the 11% 2-s condition. The responses consisted of an early posterior negative wave (180-280 ms) followed by a larger anterior positive wave. These results have important implications for fast-rate fMRI designs, while also providing new data on the brain's response to omitted stimuli. (C) 2003 Elsevier Science (USA). All rights reserved.