Chaotic fluctuations mark the sign of mental activity in task-based heart rate variability

Fig. 1. Figures to explain the experiment.(a) Procedure of measuring RRIs in Experiment 1 and Experiment 2. Participants took a 5-minute break between 7-minute RRI measurements in each condition.(b-1) Posture for measuring RRIs in the Rest condition.(b-2) Posture for measuring RRIs in the Standing condition.(b-3) Posture for measuring RRIs in the Cognitive Task condition.(c) Illustration showing the method of mental arithmetic performed in Cognitive Task 1.(d) Explanation and example of Sudoku performed in Cognitive Task 2.

Fig. 2. Box-and-whisker plot of the results of Experiment 1 and Experiment 2. Left side: The indices included in the time-domain analysis. Centre: The indices included in the frequency-domain analysis. Right side: The indices included in the chaos/complexity analysis. The number of data points (sample size) was 27. The horizontal axis labels are explained as follows: R1 represents Rest 1, R2 represents Rest 2, CT1 represents Cognitive Task 1, CT2 represents Cognitive Task 2, and S represents Standing.

Fig. 3. Typical examples of RRI Poincaré plots in Rest 1, Standing, and Cognitive Task 1. The Poincaré plot is a return map that plots points at the positions (x-axis, y-axis) = \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(u_1, u_2), (u_2, u_3), (u_3, u_4),\cdots$$\end{document} where \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\{u_1, u_2, u_3, u_4...\}$$\end{document} are time series RRI data. Let us look at the ellipse with orange dotted line. SD1 is the standard deviation along the minor axis. SD2 is the standard deviation along the major axis. An increase in the thickness of the Poincaré plot in the minor axis direction, that is, an increase in SD1/SD2 means that the change from the current RRI value \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb}…

Fig. 4. Histogram of the chaos indicator ratio (CIR) using 6 indices included in the chaos/complexity analysis. Upper: CIR of Rest to Standing (blue) and Rest to Cognitive Task 1 (red). Lower: CIR of Rest to Standing (blue) and Rest to Cognitive Task 2 (red). CCI means any of the six indices included in the chaos/complexity analysis.

Fig. 5. Expanded neurovisceral integration model incorporating findings from large-scale brain networks and fMRI studies. This schematic, drawn by the authors, illustrates an expanded version of the original neurovisceral integration model31. This model suggests that DMN activation (Rest) leads to deactivation of sympathetic nerve activity and activation of parasympathetic nerve activity. Conversely, CEN and SN activation (Cognitive Task) lead to activation of sympathetic nerve activity and deactivation of parasympathetic nerve activity. However, in the present experiment, these predicted changes in autonomic nerve activity were not significantly detected using conventional HRV analysis. Therefore, the chaoticity of HRV is presumed to reflect mechanisms other than a simple activation/deactivation pattern of the autonomic nervous system.

Fig. 6. A conceptual framework that explains that higher-order brain function brings chaos to HRV. (a) In the Rest condition, the default mode network (DMN) is the most active. In addition, the DMN, central executive network (CEN) and salience network (SN) are moderately connected. Therefore, since the activity of the higher-order brain system, which consists of the DMN, CEN and SN, is controlled by one strong mode (DMN), the chaoticity in the system is small or does not appear. (b) In the Cognitive Task condition without imposed stressor, the DMN, CEN and SN are equally active. In addition, the DMN, CEN and SN are connected at the same strength as in Rest. That is, the higher-order brain system has three equal powered modes and is in a state of antagonism. In this case, the strong chaos may be caused in the system. According to the neurovisceral integration model, it can be explained that the chaos caused in the higher-order brain system brings chaos in autonomic nervous system, and finally, HRV becomes chaotic. (c) In the Cognitive Task condition with imposed stressor, the DMN, CEN and SN are equally active. However, the DMN and SN are strongly connected, and the connection to the CEN…