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

## TL;DR

This paper shows that heart rate variability during mental tasks reveals chaotic patterns, suggesting a new way to study brain-heart interactions.

## Contribution

The study introduces a new hypothesis linking chaotic HRV features to cognitive processes.

## Key findings

- Chaos/complexity indices increase significantly during mental tasks.
- Conventional HRV measures do not change during mental tasks.
- Chaotic dynamics in HRV are relevant for understanding brain-heart interactions.

## Abstract

Heart rate variability (HRV), regulated by the autonomic nervous system, is typically assessed using standard time-domain and frequency-domain methods to evaluate autonomic function. However, conventional linear analyses capture only a limited aspect of HRV, as the human body, including the cardiovascular system, is intrinsically nonlinear. In light of this, there has been growing interest in nonlinear analyses grounded in chaos theory and complexity science. In this study, we conducted a comprehensive comparison of time-domain, frequency-domain, and chaos/complexity indices derived from R-R interval (RRI) analysis during both physical and mental tasks. The results clearly demonstrate a significant increase in chaos/complexity indices during mental tasks, while conventional indices remain unchanged—underscoring the unique sensitivity of nonlinear measures to cognitive processes. These findings highlight the relevance of chaotic dynamics and complexity in HRV as a valuable perspective for understanding brain-heart interactions. Furthermore, based on the experimental findings, we propose a new hypothesis, consistent with previous research, regarding the emergence of chaotic features in HRV during cognitive activity.