Advancements in microelectrode array (MEA) neural probes have allowed the number of neurons that can be simultaneously recorded by implantable electrodes to roughly double every 7 years since the 1970s, with present state of the art devices allowing for simultaneous recording from thousands of neurons. Unfortunately, continued growth in MEA recording performance faces tremendous challenges from the interrelated constraints on invasiveness of implantation (i.e. probe size) combined with the need for higher capacity and density electronic voltage recording and data read-out circuitry. Specifically, the impedance and resulting noise of conventional electrodes increase dramatically as electrode size is reduced. Furthermore, higher density electrode read-out requires a large number of parallel electrical traces with high impedance and capacitive crosstalk. This has led to the need for relatively large size, weight, and power multiplexing circuitry integrated into the base and even the shank of the probe, which is both physically cumbersome and can cause significant tissue heating from power dissipation. The focus of this proposal is to develop a scalable, passively wavelength multiplexed, ultrahigh-bandwidth silicon photonic probe architecture that is capable of relaying optically-encoded voltage information from thousands of electrode sensing sites through an ultrathin, lightweight, and flexible optical fiber. We term this approach NeuroPhIBER (NeuroPhotonic Interface for Bio-Electronic Recording). Notably, the proposed architecture leverages existing mature fiber optic telecommunications and CMOS-compatible silicon photonic technologies to create a fully passive probe where all active signal processing is performed remotely.
First (Aim 1), we will develop the NeuroPhIBER MEA sensing site unit cell. This will involve creating a silicon photonic modulator with Q ~ 25,000 to serve as a sensitive voltage sensor for converting our extracellular neural voltage signals to an optical signal that is subsequently coupled to an optical fiber and remoted to the detection/signal processing station.
Second (Aim 2), we will multiplex the unit cell within the NeuroPhIBER MEA probe up to a goal of 32 passively wavelength multiplexed devices onto a single bus waveguide. This will enable us to record from 100s of sensing sites using multiple spatially multiplexed bus waveguides on a single probe shank, enabling high spatio-temporal resolution neurological recording. Lastly (Aim 3), we will perform an in vitro validation of our NeuroPhIBER MEA probe using primary murine cortical cultures. This will enable us to quantitatively study individual neurons and function in a controlled environment.
Gaining a comprehensive understanding of the brain and behavior requires detailed observation of the interrelationships between large numbers of neurons spread across various regions of the brain with high spatio- temporal resolution. State of the art microelectrode array (MEA) probes are capable of capturing information from thousands of electrode sensing sites but are severely challenged by bottlenecks in electronic readout given the size constraints of a minimally invasive probe. The fiber-optically coupled NeuroPhIBER MEA hardware developed through this program will enable dramatic reduction of the size, weight, and power of neural MEA probes allowing for a greater number of sensing sites and parallel probes thus dramatically increasing in the number of neurons that can be read.
