Standardized EEG Protocol for Comparing Cortical Responses to Mechanical and Electrical Tactile Stimuli

Summary

This proof-of-concept protocol details EEG recording of somatosensory evoked potentials elicited by electrical and mechanical stimulation using oddball and roving paradigms.

Abstract

The development of realistic tactile feedback in haptic interfaces is contingent on understanding the neural processing of electrical versus mechanical stimuli. A protocol is presented for directly comparing the two modalities using electroencephalography (EEG). The protocol details procedures to achieve precise EEG-stimulator synchronization, calibrate subject-specific electrical and mechanical stimuli, and implement both oddball and roving paradigms to compare early event-related potential (ERPs) and the mismatch negativity (MMN) component. The proof-of-concept protocol was validated on four healthy participants, each assigned to a distinct experimental condition: mechanical or electrical stimulation of the right index fingertip under roving or oddball paradigms, manipulating duration (100 ms vs. 145 ms). Additionally, a 5^th participant underwent a roving paradigm with alternating modalities with all stimuli at 100 ms. Under unimodal stimulation, the roving paradigm proved more sensitive than the oddball in detecting somatosensory ERPs for both modalities and a discernible MMN-like component for electrical stimulation. The cross-modal comparison using the roving paradigm similarly revealed a clear MMN-like component but only for the electrical stimulus. These results demonstrate that the current protocol is suitable for correlating neural activity with perception and for directly comparing the cortical processing of artificial and natural sensations. This framework is a necessary step toward developing electrical stimulation protocols that elicit cortical responses indistinguishable from mechanical touch.

Introduction

A fundamental challenge in haptic technology is recreating natural tactile sensations through skin-machine interfaces. This requires replicating the precise spatiotemporal patterns of neural activity that natural stimuli evoke. While mechanical actuators can replicate physical interactions, epidermal electrical stimulation of mechanoreceptors presents a compact and versatile alternative¹. However, electrical stimulation often elicits unnatural or unpleasant paresthesia. A direct comparison of neural responses to electrical and mechanical stimulation represents a novel area of interest^2,3....

Protocol

The current experimental protocol was conducted in accordance with the ethical guidelines of the Sirius University Human Investigation Committee (Approval Date: 10.06.2025). Written informed consent is obtained from each participant prior to data collection. Exclusion criteria included the presence of implanted cardiac pacemakers or other electronic devices, a history of epilepsy or seizure disorders, pregnancy, or dermatological conditions at the stimulation site.

1. Multimodal stimulation system

1. Use a custom-built multimodal stimulator developed to deliver precisely controlled and synchronized somatosensory st....

Results

Oddball paradigm
The presentation of rare deviant stimuli (145 ms) among frequent standard stimuli (100 ms) during mechanical stimulation failed to elicit clear and reliable ERPs. Consequently, no significant difference was observed between standard and deviant responses (Figure 1). In contrast, the electrical oddball paradigm generated discernible bilateral ERP waveforms. However, comparing standard and deviant stimuli still did not yield a significant or consistent MMN.......

Discussion

This work establishes a standardized EEG protocol for the direct, within-subject neural comparison of artificial electrical and natural mechanical tactile stimulation. The core methodological contribution is a framework that ensures precise temporal control, participant-specific perceptual calibration, and the application of different experimental paradigms to assess cortical responses. The initial proof-of-concept results, while based on a limited sample, demonstrate the protocol's efficacy and highlight its potenti.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
actiCHamp Plus Versatile all-in-one lab amplifier	Brain Products GmbH	S/N ACBM17120955	Primary EEG data acquisition system
actiCAP slim / snap	Brain Products GmbH	BP-185-2200	Active electrode cap with 64 channels
Digitimer DS7A	Digitimer Ltd	UDI-DI 5060490360003	Electrical stimulator
MatLab	The MathWorks, Inc., Natick, MA, USA
Mini-shaker type 4810	Brüel & Kjær	BP-0232	Mechanical stimulator
Photo Sensor	Brain Products GmbH	N/A	For optical detection of stimulus onset
Shielded-room Neiroiconica "Expert	Neiroiconica Assistive Ltd	S/N 20210119011	Electromagnetically shielded chamber
TriggerBox Plus	Brain Products GmbH	S/N TB-A100009-0624	Synchronization interface for TTL triggers