Pospelov Nikita, Tetereva Alina, Martynova Olga, Anokhin Konstantin
Institute for Advanced Brain Studies, Lomonosov Moscow State University, Moscow, Russia.
Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Science, Russia.
Neuroimage Rep. 2021 Jul 13;1(3):100035. doi: 10.1016/j.ynirp.2021.100035. eCollection 2021 Sep.
The brain at wakefulness is active even in the absence of goal-directed behavior or salient stimuli. However, patterns of this resting-state (RS) activity can undergo long-term alterations following exposure to preceding meaningful stimuli. This study was aimed to develop an unbiased method to detect such changes in the RS activity after exposure to emotionally meaningful stimuli. For this purpose, we used functional magnetic resonance imaging (fMRI) of RS brain activity before and after acquisition and extinction of experimental conditioned fear. A group of healthy volunteers participated in three fMRI sessions: a RS before fear conditioning, a fear extinction session, and a RS immediately after fear extinction. The fear-conditioning paradigm consisted of three neutral visual stimuli paired with a partial reinforcement by a mild electric current. We used both linear and non-linear dimensionality reduction approaches to distinguish between the initial RS and the RS after stimuli exposure. The principal component analysis (PCA) as a linear dimensionality reduction method showed significantly worse results than non-linear methods (Isomap, LLE, Laplacian eigenmaps). Using the Laplacian eigenmaps manifold learning method, we were able to show significant differences between the two RSs at the level of individual participants. This detection was further improved by smoothing the BOLD signal with the wavelet multiresolution analysis. The developed method can improve the discrimination of functional states collected in longitudinal fMRI studies.
即使在没有目标导向行为或显著刺激的情况下，清醒状态下的大脑也是活跃的。然而，在接触先前有意义的刺激后，这种静息状态（RS）活动的模式可能会发生长期改变。本研究旨在开发一种无偏方法，以检测在接触情感上有意义的刺激后RS活动的此类变化。为此，我们在实验性条件性恐惧的习得和消退前后，对RS脑活动进行了功能磁共振成像（fMRI）。一组健康志愿者参加了三次fMRI实验：恐惧条件化前的RS、恐惧消退实验以及恐惧消退后的RS。恐惧条件化范式由三个中性视觉刺激与轻度电流的部分强化配对组成。我们使用线性和非线性降维方法来区分初始RS和刺激暴露后的RS。作为线性降维方法的主成分分析（PCA）显示，其结果明显不如非线性方法（等距映射、局部线性嵌入、拉普拉斯特征映射）。使用拉普拉斯特征映射流形学习方法，我们能够在个体参与者水平上显示两个RS之间的显著差异。通过小波多分辨率分析对血氧水平依赖（BOLD）信号进行平滑处理，进一步提高了这种检测效果。所开发的方法可以改善纵向fMRI研究中收集的功能状态的辨别能力。
