Integrating Cardiac Cycle Phases into Event Related Potential Analysis: A Protocol for Two-Dimensional and Virtual Reality Environments

Summary

This protocol describes an approach to investigate cardiac phase-dependent modulation of visual event-related potentials utilizing simultaneous electroencephalography and electrocardiography recordings. The protocol details stimulus synchronization, cardiac phase segmentation, and event-related potentials analysis during systole and diastole, and is applicable in both conventional two-dimensional and immersive virtual reality environments.

Abstract

The heartbeat is a fundamental physiological rhythm that not only sustains life but also modulates perceptual and neural processes, thereby influencing the reproducibility of event-related potentials (ERPs). While virtual reality (VR) offers highly immersive environments compared to conventional two-dimensional (2D) screens, it also introduces unique challenges for electrophysiological recording, including motion artifacts, presentation latency, and potentially stronger cardiogenic modulation. These factors can diminish the efficiency of standard electroencephalography (EEG) preprocessing, leading to substantial data loss. This study presents a detailed protocol that combines simultaneous EEG and electrocardiography (ECG) to investigate heart-brain interactions under both VR and 2D conditions. The approach involves precise alignment of stimuli with cardiac signals, correction for VR-induced latency, and extended artifact management. Segmentation of EEG epochs based on whether stimuli occurred during cardiac systole or diastole revealed a robust suppression of visual ERP amplitude during systole. Critically, this suppressive effect was nearly identical in both VR and 2D environments, demonstrating the protocol's efficacy and confirming that this fundamental heart-brain interaction is resilient to changes in immersion level. This protocol, thus, offers a standardized framework for investigating cardiac influence on cognition, adaptable to diverse visual presentation methods.

Introduction

The rhythmic activity of the heart is increasingly recognized not only as a vital homeostatic process but as a fundamental modulator of brain function and cognition¹. A growing body of evidence demonstrates that cardiac signals exert a continuous influence on a wide spectrum of neurocognitive processes, including perception, attention, emotional regulation, and consciousness^2,3. This heart-brain axis is mediated by afferent interoceptive signals from cardiovascular baroreceptors and mechanoreceptors, which project via the brainstem to cortical areas where they integrate with ex....

Protocol

The study was approved by the Bioethics Committee of the Samara State Medical University (protocol code 195, dated 10 October 2018). All participants provided informed voluntary consent prior to the study. The final sample consisted of 27 healthy male volunteers aged 19-21 years. During the testing sessions, each participant completed a series of standardized assessments administered individually. The reagents and the equipment used are listed in the Table of Materials.

1. Materials and equipment

NOTE: Use functionally equivalent hardware and software when appropriate. Refer to

Results

The present study employed an analysis protocol to investigate ERP modulation by afferent interoceptive signals during the cardiac cycle phase (systole vs. diastole) across two experimental environments: a standard 2D monitor and an immersive VR setting. EEG epochs were extracted and analyzed relative to the R-peak of the concurrently recorded ECG.

The nonparametric cluster-based permutation test applied to visual ERPs recorded at occipital electrodes (O1, Oz, O2) across the entire epoch revea.......

Discussion

Critical steps within the protocol
Several steps of the proposed protocol are critical for obtaining valid cardiac phase-dependent ERP effects. First, precise synchronization between stimulus presentation and EEG recording is essential, and environment-specific display latency must be quantified using a photodiode and corrected at the event-marker level, as uncorrected delays or excessive jitter can lead to temporal smearing of ERP components. Second, accurate detection of ECG R-peaks and reliable .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
actiCAP slim / snap	Brain Products GmbH	BP-185-2200	Active electrode cap with 64 channels.
actiCHamp Plus Versatile all-in-one lab amplifier	Brain Products GmbH	S/N ACBM17120955	Primary EEG data acquisition system.
Ag/AgCl electodes disposable 26 mm	Nika-Medical Ltd	N/A	Disposable electrodes for three-lead ECG
BIP2AUX adapter	Brain Products GmbH	N/A	Connects ECG output to EEG aux input.
Desktop ROG Srtix	ASUSTeK Computer Inc.	G835LR-SA117	High-performance workstation. Used for simultaneous operation of the VR system (HTC Vive), stimulus presentation software, and EEG recording platform (BrainVision Recorder).
HTC Vive  Pro Eye	HTC Corporation	S/N FA1142100443	VR system for immersive stimulus presentation.
Photo Sensor	Brain Products GmbH	N/A	For optical detection of stimulus onset.
Samsung 27" ViewFinity S8	Samsung Electronics Co., Ltd	S/N 0UYMHNBXB00044D	Primary display for the 2D condition.
Samsung 27" ViewFinity S8	Samsung Electronics Co., Ltd	S/N 0UYMHNBXB00030E	Experimenter's display. Used for running EEG recording software and monitoring data during experiments.
Shielded-room Neiroiconica "Expert"	Neiroiconica Assistive Ltd	S/N K20210119011	Electromagnetically shielded chamber.
Snap Lead Cable	Neurosoft ltd	N/A	Connects ECG electrodes to the adapter
TriggerBox Plus	Brain Products GmbH	S/N TB-A100009-0624	Synchronization interface for TTL triggers.