Referencing--Thin-film grids, ECoG neural recording/stimulation

Technical Note

Document Title: Referencing – Thin-Film Grids for ECoG Neural Recording/Stimulation

Document Number: NN-TN-2025-007

Version: 1.0

Date: March 16, 2025

Author: NeuroNexus Technical Support Team

Revision History: N/A (Initial Release)

Status: Approved for Publication

Intended Audience: Researchers conducting electrocorticography (ECoG) neural recordings and stimulation using NeuroNexus thin-film grids

Application Area: Electrophysiology techniques, electrodes, micro-scale neural interfaces, brain-computer interfaces

Associated Resources:

• surgical guide as a pdf document
• NeuroNexus website

For additional technical support, visit the NeuroNexus Resource Center.

1. Introduction

This technical note provides an overview of best practices for configuring reference and ground connections when using NeuroNexus thin-film grids in ECoG neural recording and stimulation experiments. Proper referencing is essential for obtaining high-quality cortical signals and minimizing stimulation artifacts.

Detailed configurations may vary by laboratory based on experimental design, equipment, and institutional protocols. This document outlines a general approach to illustrate proper referencing and grounding within the basic procedural framework. Researchers should adapt these recommendations to their specific methodologies while complying with all applicable ethical and regulatory guidelines.

2. Importance of Proper Referencing

For ECoG neural recording and stimulation, the reference electrode provides a baseline for neural activity measurements, while the ground electrode serves as a common electrical return path. Improper referencing can lead to:

• Increased Noise: Reduced signal-to-noise ratio (SNR) due to environmental interference.
• Stimulation Artifacts: Electrical artifacts obscuring neural signals during stimulation.

Proper referencing ensures accurate data acquisition and reliable interpretation of cortical activity.

3. Reference and Ground Configurations

a. Reference Electrode Placement

• Separate Reference Electrode:
  • Placement: A stainless steel or Ag/AgCl wire can be inserted into a small craniotomy or attached to a bone screw placed near but outside the recording area.

  • Connection: Attach the reference wire to the designated reference input on the recording system.

    No Separate Reference (Common Reference):

  • Configuration: If a separate reference is not used, the reference input on the grid can be connected to a bone screw positioned near the grid but outside the craniotomy.

    Internal Reference Site (for Grids with Built-in References):

  • Some thin-film grids include an internal reference electrode on the array itself. If used, ensure the reference site is positioned over an inactive cortical area or a designated quiet zone in the recording region.

b. Ground Electrode Placement

• Ground Electrode:
  • Placement: Secure the ground wire to a bone screw located away from the recording grid to minimize interference.
  • Connection: Attach the ground wire to the ground input on the recording system.

4. Mitigating Stimulation Artifacts

During simultaneous recording and stimulation, artifacts can occur due to electromagnetic interference. Strategies to minimize these artifacts include:

• Impedance Matching:

  • Utilize electrodes with similar impedance values to reduce differential signal drift during stimulation.

    Differential Referencing:

  • Use a differential recording configuration where possible to minimize common-mode noise and stimulation artifacts.

    Artifact Rejection Algorithms:

  • Implement real-time subtraction or post-processing techniques to remove predictable artifacts from the recorded signals.

    Faraday Shielding:

  • If external noise sources are problematic, use shielding such as a Faraday cage to isolate the setup.