arXiv subjects

Jose M. Carmena

Publications and source records attributed to Jose M. Carmena.

5 recordsLinked to original sources

arXiv2020

StimDust: A mm-scale implantable wireless precision neural stimulator with ultrasonic power and communication

Neural stimulation is a powerful technique for modulating physiological functions and for writing information into the nervous system as part of brain-machine interfaces. Current clinically approved neural stimulators require batteries and are many cubic centimetres in size -- typically much larger than their intended targets. We present a complete wireless neural stimulation system consisting of a 1.7 mm3 wireless, batteryless, leadless implantable stimulator (the "mote"), an ultrasonic wireless link for power and bi-directional communication, and a hand-held external transceiver. The mote consists of a piezoceramic transducer, an energy storage capacitor, and a stimulator integrated circuit (IC). The IC harvests ultrasonic power with high efficiency, decodes stimulation parameter downlink data, and generates current-controlled stimulation pulses. Stimulation parameters are time-encoded on the fly through the wireless link rather than being programmed and stored on the mote, reducing power consumption and on-chip memory requirements and enabling complex stimulation protocols with high-temporal resolution and low-latency feedback for use in closed-loop stimulation. Uplink data indicates whether the mote is currently stimulating; it is encoded by the mote via backscatter modulation and is demodulated at the external transceiver. We show that the mote operates at an acoustic intensity that is 7.8% of the FDA limit for diagnostic ultrasound and characterize the acoustic wireless link's robustness to expected real-world misalignment. We demonstrate the in vivo performance of the system with motes acutely implanted with a cuff on the sciatic nerve of anesthetized rats and show highly repeatable stimulation across a wide range of physiological responses.

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arXiv2019

A Sub-mm$^3$ Ultrasonic Free-floating Implant for Multi-mote Neural Recording

A 0.8 mm$^3$ wireless, ultrasonically powered, free-floating neural recording implant is presented. The device is comprised only of a 0.25 mm$^2$ recording IC and a single piezoceramic resonator that is used for both power harvesting and data transmission. Uplink data transmission is performed by analog amplitude modulation of the ultrasound echo. Using a 1.78 MHz main carrier, >35 kbps/mote equivalent uplink data rate is achieved. A technique to linearize the echo amplitude modulation is introduced, resulting in <1.2\% static nonlinearity of the received signal over a $\pm$10 mV input range. The IC dissipates 37.7 $μ$W, while the neural recording front-end consumes 4 $μ$W and achieves a noise floor of 5.3 $μ$V$_{rms}$ in a 5 kHz bandwidth. This work improves sub-mm recording mote depth by >2.5x, resulting in the highest measured depth/volume ratio by $\sim$3x. Orthogonal subcarrier modulation enables simultaneous operation of multiple implants, using a single-element ultrasound external transducer. Dual-mote simultaneous power up and data transmission is demonstrated at a rate of 7 kS/s at the depth of 50 mm.

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arXiv2018

WAND: A 128-channel, closed-loop, wireless artifact-free neuromodulation device

Closed-loop neuromodulation systems aim to treat a variety of neurological conditions by dynamically delivering and adjusting therapeutic electrical stimulation in response to a patient's neural state, recorded in real-time. Existing systems are limited by low channel counts, lack of algorithmic flexibility, and distortion of recorded signals from large, persistent stimulation artifacts. Here, we describe a device that enables new research applications requiring high-throughput data streaming, low-latency biosignal processing, and truly simultaneous sensing and stimulation. The Wireless Artifact-free Neuromodulation Device (WAND) is a miniaturized, wireless neural interface capable of recording and stimulating on 128 channels with on-board processing to fully cancel stimulation artifacts, detect neural biomarkers, and automatically adjust stimulation parameters in a closed-loop fashion. It combines custom application specific integrated circuits (ASICs), an on-board FPGA, and a low-power bidirectional radio. We validate wireless, long-term recordings of local field potentials (LFP) and real-time cancellation of stimulation artifacts in a behaving nonhuman primate (NHP). We use WAND to demonstrate a closed-loop stimulation paradigm to disrupt movement preparatory activity during a delayed-reach task in a NHP in vivo. This wireless device, leveraging custom ASICs for both neural recording and electrical stimulation modalities, makes possible a neural interface platform technology to significantly advance both neuroscientific discovery and preclinical investigations of stimulation-based therapeutic interventions.

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arXiv2013

Physical Principles for Scalable Neural Recording

Simultaneously measuring the activities of all neurons in a mammalian brain at millisecond resolution is a challenge beyond the limits of existing techniques in neuroscience. Entirely new approaches may be required, motivating an analysis of the fundamental physical constraints on the problem. We outline the physical principles governing brain activity mapping using optical, electrical,magnetic resonance, and molecular modalities of neural recording. Focusing on the mouse brain, we analyze the scalability of each method, concentrating on the limitations imposed by spatiotemporal resolution, energy dissipation, and volume displacement. We also study the physics of powering and communicating with microscale devices embedded in brain tissue.

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arXiv2013

Neural Dust: An Ultrasonic, Low Power Solution for Chronic Brain-Machine Interfaces

A major hurdle in brain-machine interfaces (BMI) is the lack of an implantable neural interface system that remains viable for a lifetime. This paper explores the fundamental system design trade-offs and ultimate size, power, and bandwidth scaling limits of neural recording systems built from low-power CMOS circuitry coupled with ultrasonic power delivery and backscatter communication. In particular, we propose an ultra-miniature as well as extremely compliant system that enables massive scaling in the number of neural recordings from the brain while providing a path towards truly chronic BMI. These goals are achieved via two fundamental technology innovations: 1) thousands of 10 - 100 μm scale, free-floating, independent sensor nodes, or neural dust, that detect and report local extracellular electrophysiological data, and 2) a sub-cranial interrogator that establishes power and communication links with the neural dust.

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