Soft Depth Neural Probes Enable Chronic Recordings from the Rat Brainstem

Area of Science:

• Neuroscience
• Biomedical Engineering
• Materials Science

Background:

• Long-term neural recordings are crucial for understanding brain function but are limited by electrode degradation and micro-motion, especially in deep brain structures.
• Current neural implants face challenges with stability, biointegration, and recording quality degradation over time, hindering chronic in vivo applications.
• Miniaturization and biomimetic softness are promising strategies to enhance the performance and longevity of neural interfaces.

Purpose of the Study:

• To develop and validate a novel penetrating neural probe design combining microfabrication with soft hydrogel encapsulation for improved chronic recordings.
• To address the challenges of surgical access, micro-motion, and biofouling in deep brain recordings.
• To demonstrate the efficacy of the soft-flex probe for stable, high-quality neurophysiological recordings in deep brain structures and multimodal circuit analysis.

Main Methods:

• Fabrication of microelectrode arrays on flexible polyimide with a micrometric zwitterionic hydrogel soft-shell encapsulation.
• Development and validation of a surgical insertion strategy and tooling for implanting soft depth probes into the gigantocellular (Gi) nucleus.
• Chronic electrophysiological recordings in rat models and multimodal experiments combining optogenetics with brainstem electrophysiology in mice.

Main Results:

• Stable, high signal-to-noise ratio neurophysiological recordings were achieved for at least 8 weeks using the soft depth probes.
• The hybrid soft-flex microfabrication technology demonstrated improved biointegration and reduced tissue response.
• Successful demonstration of a multimodal system for studying cortico-brainstem circuitry, coupling optogenetic stimulation with deep brain electrophysiology.

Conclusions:

• The proposed hybrid soft-flex microfabrication technology significantly enhances the longevity and quality of chronic neural recordings in deep neural circuits.
• Biomimetic softness and miniaturization are effective strategies for improving the stability and biointegration of neural implants.
• This technology offers a promising solution for advancing chronic deep brain interfacing and neural circuit research.