Functional magnetic resonance imaging (fMRI) time series data presents a unique opportunity to understand temporal brain connectivity, and models that uncover the complex dynamic workings of this organ are of keen interest in neuroscience. Change point models can capture and reflect the dynamic nature of brain connectivity, however methods that translate well into a high-dimensional context (where $p>>n$) are scarce. To this end, we introduce $\textit{factorized binary search}$ (FaBiSearch), a novel change point detection method in the network structure of multivariate high-dimensional time series. FaBiSearch uses non-negative matrix factorization, an unsupervised dimension reduction technique, and a new binary search algorithm to identify multiple change points. In addition, we propose a new method for network estimation for data between change points. We show that FaBiSearch outperforms another state-of-the-art method on simulated data sets and we apply FaBiSearch to a resting-state and to a task-based fMRI data set. In particular, for the task-based data set, we explore network dynamics during the reading of Chapter 9 in $\textit{Harry Potter and the Sorcerer's Stone}$ and find that change points across subjects coincide with key plot twists. Further, we find that the density of networks was positively related to the frequency of speech between characters in the story. Finally, we make all the methods discussed available in the R package $\textbf{fabisearch}$ on CRAN.
翻译:功能磁共振成像(fMRI)时间序列数据为理解大脑的时间连接性提供了一个独特的机会。 揭示该器官复杂动态功能的模型对神经科学非常感兴趣。 改变点模型可以捕捉并反映大脑连接的动态性质, 但是, 仍然缺乏能转化成高维环境的方法( $p ⁇ n$ ) 。 为此, 我们引入了 $\ textit{ 软化的二进制搜索 $ (FabiSearch), 这是多变量高维时间序列网络结构中的一种新颖的变化点检测方法。 FabiSearch 使用非负矩阵化、 不受监督的维度减少技术、 新的二进制搜索算法来识别多个变化点。 此外, 我们提出了一个新的方法, 将数据转换成高维Search 在模拟数据集中超越了另一种状态的状态, 我们将FabiSearch 应用于一个休息状态和基于任务的数据包。 特别是, 在基于任务的数据集中, 我们探索网络在恒定的轨道中, 和恒定点中, 我们查找了Starbrentreal 。