Noise reduction in neural recording

Technical Note

Document Title: Noise Reduction in Neural Recording

Document Number: NN-TN-2025-009

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 neural recordings with NeuroNexus electrode arrays

For Research Use Only: This document is intended exclusively for non-clinical, research applications and is not suitable for human or veterinary medical use.

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

Related Resources:

• surgical guide as a pdf document
• NeuroNexus website

1. Introduction

Neural recordings are highly sensitive to electrical noise, which can degrade signal quality and compromise data integrity. Identifying and minimizing noise sources is essential for obtaining high-fidelity neural signals.

This document provides an overview of common noise sources and practical strategies to reduce noise in both acute and chronic neural recording experiments. Because specific solutions depend on laboratory setups, equipment, and environmental conditions, researchers should tailor these recommendations to their particular recording configurations while adhering to institutional guidelines.

2. Common Noise Sources in Neural Recording

Noise in neural recording systems typically originates from one or more of the following sources:

a. Environmental Noise

• Power Line Interference: 50/60 Hz electrical noise from AC power sources.
• Electromagnetic Interference (EMI): Stray electromagnetic fields from nearby equipment such as monitors, power supplies, and fluorescent lights.
• Radio Frequency Interference (RFI): Wireless communication devices and radio transmitters can introduce high-frequency noise.

b. System and Equipment Noise

• Headstage and Amplifier Noise: Poor-quality or unshielded headstages and amplifiers can introduce system noise.
• Ground Loops: Multiple electrical ground connections can create a loop that picks up noise.
• Impedance Mismatch: High-impedance electrodes amplify thermal noise, reducing the signal-to-noise ratio (SNR).

c. Biological Noise

• Muscle Artifacts (EMG): Movements and muscle activity introduce low-frequency noise into neural recordings.
• Cardiac Artifacts (ECG): The electrical activity of the heart may appear in recordings, particularly in EEG or ECoG experiments.

3. Strategies for Noise Reduction

a. Environmental Noise Reduction

• Use a Faraday Cage:
  • Surrounding the recording setup with a grounded conductive enclosure can shield against external electromagnetic interference.
• Minimize Electrical Equipment Near the Setup:
  • Keep power supplies, monitors, and non-essential electronics at least 1–2 meters away from the recording system.
• Use Battery Power When Possible:
  • Powering amplifiers and headstages with batteries instead of AC power can significantly reduce noise.

b. System and Equipment Optimization

• Proper Grounding and Referencing:
  • Use a single ground connection to avoid ground loops.
  • Place the reference electrode in a stable, low-noise region.
• Impedance Matching:
  • Ensure electrode impedance is within the recommended range for the recording system (typically 0.1–2 MΩ for extracellular recordings).
• Use Shielded Cables:
  • Twisted-pair or shielded cables reduce EMI pickup along signal transmission lines.
• Pre-Amplification Near the Recording Site:
  • Using a low-noise headstage near the electrode array boosts signals before long-distance transmission, reducing interference effects.

c. Biological Noise Reduction

• Minimize Subject Movement:
  • Use a stable fixation method in acute experiments or allow sufficient recovery in chronic setups.
• Filter Unwanted Frequency Bands:
  • High-pass filters (e.g., >300 Hz) can remove slow drift and movement artifacts.
  • Notch filters can reduce 50/60 Hz power line interference, but should be used cautiously to avoid distorting neural signals.
• Avoid EMG and ECG Contamination:
  • Adjust electrode placement to minimize muscle activity interference.

4. Validation and Quality Control

To ensure effective noise reduction:

• Perform System Calibration: Test baseline noise levels before data collection.
• Check Impedance Regularly: High electrode impedance can increase noise levels.
• Monitor Signal Quality: Visually inspect waveforms and power spectra to detect unwanted noise sources.