ASCENT: Ultra-high Throughput Neural Recording using Flexible, Polymer-based Shanks as Terahertz Dielectric Waveguides

Brain Machine Interfaces (BMI) are used to record the electrical signals of the neurons in the brain and gain insights into the complex processes occurring in the brain and nervous system. This understanding is crucial to repair or augment cognitive and/or sensory and motor functions, which might be necessary, e.g., due to damage to the brain sustained by injuries or diseases.

Traditional recording by electroencephalography (EEG) or functional magnetic resonance imaging (MRI) is too crude, cumbersome, and slow for many of these tasks; therefore, BMIs with implanted microelectrodes need to be used. However, state of the art implantable electrode arrays (IEAs) made from rigid silicon not only have short lifetimes but can also damage the brain tissue and cause scar formation.

Recently, IEAs have been developed using flexible polymer-based shanks which minimize tissue damage during implantation, significantly increasing safety and paving the way towards long-term recording. Unfortunately, the number of electrodes, and thus the amount of data that can be recorded, is very limited. To pave the way for new basic science discoveries in neuroscience and the development of new, safe BMIs to treat individuals with brain injury or disease, this project introduces a new, completely wireless approach that has virtually unlimited data bandwidth for communicating data outside of the brain and enables safe, long term brain recording via biocompatible, flexible polymer electrodes.

The system is expected to have a huge impact on advancing the state-of-the-art in IEA technology by enabling, for the first time ever, safe and high-density neural recording over multiple year-long durations. The technological advances in hybrid silicon-polymer fabrication and chip-to-chip communication via polymer waveguides will also hold scientific and practical application value in their own right.

A major problem facing brain machine interfaces is achieving both high data throughput and long lifespans when recording neural activity. To overcome current limitations on recording density and lifetime, this project will develop and prototype a new implantable electrode array technology that combines active silicon complementary metal oxide semiconductor (CMOS)-based electrodes with a biocompatible polymer shank.

The Parylene C polymer is flexible and can be microfabricated such that multiple custom, fully wireless CMOS neural recording chiplets can be arranged along the length of each shank. The polymer shank, acting as a dielectric waveguide, will carry both red light and Terahertz (THz) radio-frequency energy from outside the brain to the chiplets for power harvesting and backscatter data communication, respectively, obviating the need for wires.

On-chip photodiodes will rectify the incident optical light for powering each chip, and on-chip THz antennas will be used to modulate the locally recorded and amplified neuronal data onto the THz carrier signal inside the polymer shank via backscatter communication. Extensive modeling will be done of the electromagnetic characteristics of the polymer shank waveguides at both optical and THz wavelengths in order to optimize the shank cross-section and design of the THz surface coupling antennas for maximizing system efficiency and communication bandwidth.

Each chiplet will contain a dense neural recording electrode array with active amplification, filtering, and spike detection circuitry for recording, digitizing, and compressing neuronal data before modulating it on the THz carrier signal and sending it to the base via the polymer shank waveguide. Importantly, this paradigm achieves a completely wireless system that maximizes the number of neural recording sites and contributes a new hybrid silicon-polymer architecture capable of efficient, high-bandwidth quasi-optical chip-to-chip communication.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.