Task-dependent fractal patterns of information processing in working memory

TL;DR

This study uses advanced fractal and spectral analysis techniques on fMRI data to reveal how working memory engagement varies regionally and differs between verbal and nonverbal tasks, providing more sensitive insights than traditional correlations.

Contribution

It demonstrates that fractal and cross-correlation analyses of fMRI signals can distinguish cognitive task engagement and task type with higher sensitivity than conventional methods.

Findings

Fractal scaling varies regionally with task engagement.

Differences between verbal and nonverbal memorization are evident.

Cross-correlations distinguish resting state from active tasks.

Abstract

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.