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(21) Designing Current Sensing Systems for Multiplexed Neural Interfaces

Thursday, June 12, 2025
4:30 PM - 5:10 PM ET
Location: Sky View
Introduction: As electrode density and coverage increase, flexible electronics must be incorporated at each electrode to deal with wiring constraints. However, present methods introduce significant noise and decrease device lifespan(1,2). Both are critically important for real-time systems that require high signal to noise ratios (SNR), such as closed-loop recording and stimulation devices, or in unit seizure monitoring(3,4). Moving forward, electrode arrays need to have high resolution, large spatial coverage, long lifespans, and high accuracy (SNR).

Current sensing technology leverages inherit advantages with unique circuit design to decrease electrical noise, increase electrode density, and increase device lifespan(5). This study aims to enhance the performance of neural recordings by 1) developing a multiplexed current sensing system to record evoked neural signals and 2) refining this multiplexed current sensing system to record spiking activity.

Methods: We designed, fabricated, and tested a multiplexed current recording system comprising of a flexible, active, electrode, a current sensing headstage. The current sensing headstage utilizes an X-ray detector to accept 32 multiplexed parallel inputs from the active electrode. The electrode has 256, 12um x 36um contacts multiplexed 8:1 by active transistors fabricated on Si and then transfer printed onto a flexible polyimide substrate. In vitro testing characterized the individual transistors as well as signal to noise ratio of the data acquisition system (DAQ). We completed in vivo testing measuring tone evoked responses in rodent auditory cortex(5).

Results: Our custom DAQ reproduced signals with sufficient SNR (70dB) to record neural signals. Our electrode also has sufficient performance (mobility: 583.7 ± 48.3 cm2/Vs) and uniformity (Vth: 1.56 ± 0.19 V). The combined performance of the entire system yields low noise (2.7 ± 3.4 pArms) and sufficient SNR (30.1 ± 10.4 dB). In vivo we recorded distinguishable single trial neural responses and showed an increase in neural decoding performance compared to our passive control electrodes (51% vs 35%).

The DAQ originally sampled at 400S/s allowing for local field potential neural recordings but we have since re-designed the DAQ to support 10kS/s. We are now characterizing changes in SNR with respect to multiplexing rate possibly providing an alternative to voltage sensing for highly multiplexed devices. Finally, we are in the process of further in vivo testing to capture spiking activity in rodent auditory cortex.

Conclusion: This work shows multiplexed current sensing can record decodable neural signals, enable flexible, active, electrodes, and operate at sufficiently high sampling rates to record spiking activity.