We applied detrended fluctuation analysis, power spectral density, and eigenanalysis of detrended cross-correlations to investigate fMRI data representing a diurnal variation of working memory in four visual tasks: two verbal and two nonverbal. We show that the degree of fractal scaling is regionally dependent on engagement in cognitive tasks. A particularly apparent difference was found between memorisation in verbal and nonverbal tasks. Furthermore, the detrended cross-correlations between brain areas were predominantly indicative of differences between resting state and other tasks, between memorisation and retrieval, and between verbal and nonverbal tasks. The fractal and spectral analyses presented in our study are consistent with previous research related to visuospatial and verbal information processing, working memory (encoding and retrieval), and executive functions, but they were found to be more sensitive than Pearson correlations and showed the potential to obtain other subtler results. We conclude that regionally dependent cognitive task engagement can be distinguished based on the fractal characteristics of BOLD signals and their detrended cross-correlation structure.

中文翻译：

---

工作记忆中信息处理的任务相关分形模式

我们应用去趋势波动分析、功率谱密度和去趋势互相关的特征分析来研究代表四个视觉任务中工作记忆的昼夜变化的 fMRI 数据：两个语言和两个非语言。我们表明，分形缩放的程度在区域上取决于对认知任务的参与。在语言和非语言任务中的记忆之间发现了特别明显的差异。此外，大脑区域之间去趋势的互相关主要表明静息状态和其他任务之间、记忆和检索之间以及语言和非语言任务之间的差异。我们研究中提出的分形和光谱分析与先前与视觉空间和语言信息处理相关的研究一致，工作记忆（编码和检索）和执行功能，但发现它们比 Pearson 相关性更敏感，并显示出获得其他更微妙结果的潜力。我们得出结论，可以根据 BOLD 信号的分形特征及其去趋势的互相关结构来区分区域依赖的认知任务参与。