Takeda Yusuke, Yamanaka Kentaro, Nozaki Daichi, Yamamoto Yoshiharu
Educational Physiology Laboratory, Graduate School of Education, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Neuroimage. 2008 Jul 1;41(3):777-88. doi: 10.1016/j.neuroimage.2008.03.012. Epub 2008 Mar 20.
Like electroencephalographic (EEG) activity during reaction time tasks, EEG activity during tasks without overt responses may also consist of two components: stimulus-locked and -unlocked components. The extraction of such stimulus-unlocked components has been difficult owing to the unknown delays. Here, we propose a novel method to extract both of the two components from single-channel EEG epochs. In this method, we initially set random values for the delays and extract uncontaminated stimulus-locked and -unlocked components using the preset delays and a discrete Fourier transform. Then, we reconstruct the EEG by overlapping the extracted components with the preset delays, and calculate the residual errors between the reconstructed and original EEG. This procedure is repeated by updating the delays until the residual errors become adequately small. After verifying the performance of this method by two kinds of simulations with artificial and EEG data, we apply the method to EEG during NoGo trials of a Go/NoGo task, and obtain the stimulus-unlocked components, the magnitudes of which are comparable with those of the stimulus-locked components. By applying this method, it is possible to study internal and subjective brain activity, which occurs with variable delays.
与反应时间任务期间的脑电图（EEG）活动一样，无明显反应任务期间的EEG活动也可能由两个成分组成：刺激锁定成分和非锁定成分。由于延迟未知，提取此类非刺激锁定成分一直很困难。在此，我们提出了一种从单通道EEG时段中提取这两个成分的新方法。在该方法中，我们首先为延迟设置随机值，并使用预设延迟和离散傅里叶变换提取未受污染的刺激锁定成分和非锁定成分。然后，我们通过将提取的成分与预设延迟重叠来重建EEG，并计算重建EEG与原始EEG之间的残余误差。通过更新延迟重复此过程，直到残余误差足够小。在用人工数据和EEG数据进行的两种模拟验证了该方法的性能后，我们将该方法应用于Go/NoGo任务的NoGo试验期间的EEG，并获得了非刺激锁定成分，其幅度与刺激锁定成分相当。通过应用此方法，可以研究以可变延迟发生的内部和主观大脑活动。
