Mäkinen Ville, Tiitinen Hannu, May Patrick
Apperception and Cortical Dynamics (ACD), Department of Psychology, PO Box 9, FIN-00014 University of Helsinki, Finland.
Neuroimage. 2005 Feb 15;24(4):961-8. doi: 10.1016/j.neuroimage.2004.10.020. Epub 2004 Dec 9.
For researchers and clinical practitioners alike, evoked and event-related responses measured with MEG and EEG provide the means for studying human brain function and dysfunction. However, the generation mechanism of event-related responses remains unclear, hindering our ability to formulate viable theories of neural information processing. Event-related responses are assumed to be generated either (1) separately of ongoing, oscillatory brain activity or (2) through stimulus-induced reorganization of ongoing activity. Here, we approached this issue through examining single-trial auditory MEG data in humans. We demonstrate that phase coherence over trials observed with commonly used signal decomposition methods (e.g., wavelets) can result from both a phase-coherent state of ongoing oscillations and from the presence of a phase-coherent event-related response which is additive to ongoing oscillations. To avoid this problem, we introduce a method based on amplitude variance to establish the relationship between ongoing oscillations and event-related responses. We found that auditory stimuli do not give rise to phase reorganization of ongoing activity. Further, increases in spectral power accompany the emergence of event-related responses, and the relationship between spectral power and the amplitude of these responses can be accounted for by a linear summation of the event-related response and ongoing oscillation with a stochastically distributed phase. Thus, on the basis of our observations, auditory event-related responses are unique descriptors of neural information processing in humans, generated by processes separate from and additive to ongoing brain activity.
对于研究人员和临床从业者而言，通过脑磁图（MEG）和脑电图（EEG）测量的诱发反应和事件相关反应为研究人类大脑功能及功能障碍提供了手段。然而，事件相关反应的产生机制仍不明确，这阻碍了我们构建可行的神经信息处理理论的能力。事件相关反应被认为是通过以下两种方式产生的：（1）与正在进行的振荡性脑活动分开产生；（2）通过刺激诱发的正在进行的活动重组产生。在此，我们通过检查人类的单次试验听觉MEG数据来探讨这个问题。我们证明，使用常用信号分解方法（如小波变换）在试验中观察到的相位相干性，既可能源于正在进行的振荡的相位相干状态，也可能源于与正在进行的振荡相加的相位相干事件相关反应的存在。为避免这个问题，我们引入了一种基于幅度方差的方法来建立正在进行的振荡与事件相关反应之间的关系。我们发现听觉刺激不会引起正在进行的活动的相位重组。此外，事件相关反应出现时伴随着频谱功率的增加，并且这些反应的频谱功率与幅度之间的关系可以通过事件相关反应与具有随机分布相位的正在进行的振荡的线性叠加来解释。因此，基于我们的观察结果，听觉事件相关反应是人类神经信息处理的独特描述符，由与正在进行的脑活动分开且相加的过程产生。
