The Effects of Cognitive Stressors on Sympathetic and Parasympathetic Nervous System

Abstract

Introduction

Heart rate variability (HRV) is a key indicator of autonomic nervous system function, commonly used as a non-invasive biomarker of health, stress response, and autonomic balance [1]. Previous research has linked cognitive demand to HRV changes, but methodological inconsistencies, such as varying cognitive tasks and lack of protocol standardization, limit comparability across studies. Our pilot study aimed to address this gap by evaluating the effects of selected cognitive stressors on parasympathetic activity, as indexed by the root mean square of successive differences (RMSSD). We hypothesized that these cognitive tasks would induce a decrease in RMSSD, indicating reduced parasympathetic activity.

Methods

Participants (N = 8) completed four cognitive tasks: two arithmetic tasks (simple equations and continuous subtraction of 13), a Stroop interference task, and a visuospatial memory task (4×4 grid). Five participants performed the visuospatial memory task first, while three began with the subtraction task. Electrocardiogram (ECG) was recorded and analysed using the BIOPAC system. HRV parameters were extracted using Kubios HRV Scientific software from 5-minute segments. The protocol included a 7-minute baseline rest, two 5-minute tasks, a 12-minute rest, two more 5-minute tasks, and a final 7-minute rest. All rest periods were conducted under identical conditions (participants were alone and instructed to remain calm and inactive) and were longer than 5 minutes to allow time for physiological settling before analysis. To introduce social pressure, three experimenters were present during task execution, but no direct comparison between social and non-social conditions was made.

Results

RMSSD during the visuospatial memory and subtraction task were compared to their respective baselines for each participant. A change threshold of ≥5% was used as an operational criterion for a meaningful difference. In the visuospatial task, 6 participants showed a decrease in RMSSD (mean: −27.3% ± 12.0%), and 2 an increase (+20.3% ± 9.2%). In the subtraction task, 5 participants showed a decrease (−29.7% ± 10.1%), 2 an increase (+46.3% ± 5.6%), and 1 remained within ±5% of baseline. No statistical tests were conducted due to the small sample size.

Limitations

The primary limitation of this study was the small sample size, which limits statistical power and generalizability. Additionally, only one trial per task was performed per participant, and only the second task in each pair was analysed for HRV.

Conclusions

Despite its limitations, this study demonstrates that both the visuospatial memory and the subtraction task effectively induce parasympathetic withdrawal, as evidenced by decreased RMSSD in most participants. However, due to the small sample size and absence of statistical testing, these results should be interpreted as exploratory and require confirmation in larger studies.

References

[1] B. Žunkovič, N. Kejžar, and F. F. Bajrović, “Standard heart rate variability parameters—Their within-session stability, reliability, and sample size required to detect the minimal clinically important effect,” J. Clin. Med., vol. 12, no. 1, pp. 1–17, 2023, doi: 10.3390/jcm12093118.