Referencing--Silicon probes, chronic neural recording/stimulation

Technical Note

Document Title: Referencing – Silicon Probes for Chronic Neural Recording/Stimulation

Document Number: NN-TN-2025-006

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 chronic neural recording and stimulation using NeuroNexus silicon probes

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

Associated Resources:

• surgical guide as a pdf document
• NeuroNexus website

1. Introduction

This technical note provides an overview of best practices for configuring reference and ground connections when using NeuroNexus silicon probes in chronic neural recording and stimulation experiments. Proper referencing is crucial for obtaining high-quality neural signals and minimizing artifacts during stimulation.

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

In chronic neural recording and stimulation, the reference electrode serves as a baseline for measuring neural activity, while the ground electrode provides a common return path for electrical currents. Incorrect referencing can lead to:

• Increased Noise: Poor signal-to-noise ratio (SNR) due to environmental interference.
• Stimulation Artifacts: Unwanted artifacts that can obscure neural signals during stimulation.

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

3. Reference and Ground Configurations

a. Reference Electrode Placement

• 16-Channel Probes:
  • Reference Wire: Chronic probes with 16 channels include a Reference Wire. Before implantation, strip a small length of insulation from the end of the Reference Wire.

  • Connection: Attach the Reference Wire to a bone screw placed contralateral to the probe implantation site, ensuring the screw does not penetrate the dura mater to avoid tissue damage.

    32-Channel Probes:

  • Reference Wire Jumper: These probes are equipped with a Reference Wire Jumper, allowing researchers to tailor the reference configuration to their specific application.
  • Internal Reference Site Model: If the probe design includes a reference site on the silicon shank, cut the white Reference Wire and connect the blue Reference Wire to a bone screw contralateral to the probe.

  • External Reference Model: If no internal reference site is present, combine the blue and white Reference Wires and connect them to a bone screw contralateral to the probe.

    64-Channel Probes:

  • Reference Wire Configuration: Similar to 32-channel probes, 64-channel probes include a Reference Wire Jumper and multiple Reference Wires.
  • Internal Reference Site Model: For probes with a reference site on the silicon shank, cut the white Reference Wire and connect the blue Reference Wires to a bone screw contralateral to the probe.
  • External Reference Model: If utilizing external references, cut the Reference Wire Jumper and attach each Reference Wire to separate bone screws contralateral to the probe.

b. Ground Electrode Placement

• Ground Wire: Chronic probes include a Ground Wire. Before implantation, strip a small length of insulation from the end of the Ground Wire.
• Connection: Attach the Ground Wire to a bone screw placed ipsilateral to the probe implantation site, ensuring the screw does not penetrate the dura mater.

4. Mitigating Stimulation Artifacts

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

• Lower Impedance: Utilize electrodes with low impedance to reduce the voltage required for stimulation, thereby decreasing artifact amplitude.
• Template Subtraction: Implement real-time template subtraction techniques to remove predictable artifacts from the recorded signals.
• Shielding: Use a Faraday cage to isolate the experimental setup from external electromagnetic interference.