4.1 Types of neural electrodes and their properties

Neural electrodes are crucial tools in neuroprosthetics, allowing us to interface with the nervous system. From intracortical electrodes that dive deep into the brain to less invasive epidural and peripheral nerve options, each type has its own strengths and weaknesses.

Choosing the right electrode involves balancing signal quality, invasiveness, and longevity. Materials like metals, polymers, and ceramics each bring unique properties to the table. Understanding these factors is key to developing effective neural interfaces for various applications.

Types of Neural Electrodes

Types of neural electrodes

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  Frontiers | Neural Interfaces for Intracortical Recording: Requirements, Fabrication Methods ... View original

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  Frontiers | Advances in Carbon-Based Microfiber Electrodes for Neural Interfacing View original

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  Frontiers | Update on Peripheral Nerve Electrodes for Closed-Loop Neuroprosthetics View original

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  Frontiers | Neural Interfaces for Intracortical Recording: Requirements, Fabrication Methods ... View original

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• Intracortical electrodes penetrate the cerebral cortex to record from individual neurons or small populations of neurons (Utah array, Michigan probe)
• Epidural electrodes are placed on the surface of the dura mater, the outermost layer of the meninges, to record from larger populations of neurons with less invasiveness compared to intracortical electrodes
• Peripheral nerve electrodes interface with peripheral nerves outside the central nervous system to record and stimulate specific nerve fibers (cuff electrodes, intraneural electrodes)

Properties of electrode materials

• Metals have high electrical conductivity (platinum, iridium, stainless steel) but may have potential issues with biocompatibility and mechanical mismatch with neural tissue
• Polymers are flexible and biocompatible (polyimide, parylene, PDMS) but have lower electrical conductivity compared to metals and may require conductive coatings or additives
• Ceramics are biocompatible and chemically inert (alumina, zirconia) but are brittle and stiff compared to neural tissue and are often used as substrates for metal or polymer electrodes

Electrode Selection and Performance

Advantages vs limitations of electrodes

• Intracortical electrodes:
  1. Advantages: provide high spatial resolution and single-unit recordings
  2. Limitations: highly invasive and have limited longevity due to tissue response
• Epidural electrodes:
  1. Advantages: less invasive than intracortical electrodes and have longer longevity
  2. Limitations: lower spatial resolution and mainly record population activity
• Peripheral nerve electrodes:
  1. Advantages: access specific nerve fibers and are suitable for stimulation and recording
  2. Limitations: invasive, potential for nerve damage, and limited selectivity

Factors in electrode selection

• Signal requirements including spatial resolution, temporal resolution, and signal-to-noise ratio
• Invasiveness and tissue damage considerations to minimize tissue response and inflammation and ensure long-term stability and functionality
• Longevity and durability factors such as resistance to mechanical stress and degradation and compatibility with chronic implantation
• Specific application demands including target neural population and location, required stimulation or recording parameters, and constraints on device size and power consumption