Minimally Invasive Brain Computer Interfaces: Evaluating the Impact of Tissue Layers on Signal Quality of Sub-Scalp EEG

TL;DR

This study evaluates sub-scalp EEG signal quality at various depths in a sheep model, comparing it with ECoG and endovascular methods, and demonstrates its potential for safe, effective brain-computer interfaces for disabled individuals.

Contribution

It provides the first comprehensive comparison of sub-scalp EEG with other invasive methods and offers insights for designing future sub-scalp electrodes for BCI use.

Findings

Sub-scalp EEG achieves ECoG-like SNR with peg electrodes.

Endovascular arrays have SNR similar to periosteal electrodes.

High gamma activity can be recorded with sub-scalp electrodes, up to 180 Hz bandwidth.

Abstract

Individuals with severe physical disabilities often experience diminished quality of life stemming from limited ability to engage with their surroundings. Brain-Computer Interface (BCI) technology aims to bridge this gap by enabling direct technology interaction. However, current BCI systems require invasive procedures, such as craniotomy or implantation of electrodes through blood vessels, posing significant risks to patients. Sub-scalp electroencephalography (EEG) offers a lower risk alternative. This study investigates the signal quality of sub-scalp EEG recordings from various depths in a sheep model, and compares results with other methods: ECoG and endovascular arrays. A computational model was also constructed to investigate the factors underlying variations in electrode performance. We demonstrate that peg electrodes placed within the sub-scalp space can achieve visual evoked potential signal-to-noise ratios (SNRs) approaching that of ECoG. Endovascular arrays exhibited SNR comparable to electrodes positioned on the periosteum. Furthermore, sub-scalp recordings captured high gamma neural activity, with maximum bandwidth ranging from 120 Hz to 180 Hz depending on electrode depth. These findings support the use of sub-scalp EEG for BCI applications, and provide valuable insights for future sub-scalp electrode design. This data lays the groundwork for human trials, ultimately paving the way for chronic, in-home BCIs that empower individuals with physical disabilities.