Neural Recording Probes Research Articles

A 0.19×0.17mm2 Wireless Neural Recording IC for Motor Prediction with Near-Infrared-Based Power and Data Telemetry.

Brain machine interfaces using neural recording systems [1]–[4] can enable motor prediction [5]–[6] for accurate arm and hand control in paralyzed or severely injured individuals. However, implantable systems have historically used wires for data communication and power, increasing risks of tissue damage, infection, and cerebrospinal fluid leakage, rendering these devices unsuitable for long-term implantation (Fig. 26.9.1, top). Recently, several wireless and miniaturized neural recording implants with various power and data transmission methods were proposed. References [7], [8] propose an electrocorticography (ECoG) recording system with near-field RF power transfer and bilateral communication, but the 0.5W Tx exceeds maximum exposure limits by 10x [8]. Ultrasonic telemetry can safely send more power than RF; however it requires mm-scale dimensions (0.8mm3 in [9]) due to bulky ultrasound transducers. On the other hand, near infrared (NIR) light can provide power transfer and data downlink via a photovoltaic cell (PV), and a data uplink via a light-emitting diode (LED). Dimensions can be scaled to 100s of microns [10], with [11] demonstrating a 0.0297mm2 neural recording system using a 50mW/mm2 light source $( of safety limit for the brain). However, this system is limited to a single channel, and since it only has a surface electrode, it can record only surface potentials (face-down, potentially blocking the light channel) or must itself be injected into brain tissue, creating significant tissue damage and danger of bleeding. In this paper, we propose $0.74\mu \mathrm{W}, 0.19\times 0.17\mathrm{mm}^{2}1\mathrm{C}$ designed for a wireless neural recording probe. It computes so-called spiking band power (SBP) [5], [12] on-chip to save 920x power while maintaining accurate finger position and velocity decoding.

Aptamer-functionalized neural recording electrodes for the direct measurement of cocaine in vivo.

Cocaine is a highly addictive psychostimulant that acts through competitive inhibition of the dopamine transporter. In order to fully understand the region specific neuropathology of cocaine abuse and addiction, it is unequivocally necessary to develop cocaine sensing technology capable of directly measuring real-time cocaine transient events local to different brain regions throughout the pharmacokinetic time course of exposure. We have developed an electrochemical aptamer-based in vivo cocaine sensor on a silicon based neural recording probe platform capable of directly measuring cocaine from discrete brain locations using square wave voltammetry (SWV). The sensitivity of the sensor for cocaine follows a modified exponential Langmuir model relationship and complete aptamer-target binding occurs in < 2 sec and unbinding in < 4 sec. The resulting temporal resolution is a 75X increase from traditional microdialysis sampling methods. When implanted in the rat dorsal striatum, the cocaine sensor exhibits stable SWV signal drift (modeled using a logarithmic exponential equation) and is capable of measuring real-time in vivo response to repeated local cocaine infusion as well as systemic IV cocaine injection. The in vivo sensor is capable of obtaining reproducible measurements over a period approaching 3 hours, after which signal amplitude significantly decreases likely due to tissue encapsulation. Finally, aptamer functionalized neural recording probes successfully detect spontaneous and evoked neural activity in the brain. This dual functionality makes the cocaine sensor a powerful tool capable of monitoring both biochemical and electrophysiological signals with high spatial and temporal resolution.

Toward a distributed free-floating wireless implantable neural recording system.

To understand the complex correlations between neural networks across different regions in the brain and their functions at high spatiotemporal resolution, a tool is needed for obtaining long-term single unit activity (SUA) across the entire brain area. The concept and preliminary design of a distributed free-floating wireless implantable neural recording (FF-WINeR) system are presented, which can enabling SUA acquisition by dispersedly implanting tens to hundreds of untethered 1 mm3 neural recording probes, floating with the brain and operating wirelessly across the cortical surface. For powering FF-WINeR probes, a 3-coil link with an intermediate high-Q resonator provides a minimum S21 of -22.22 dB (in the body medium) and -21.23 dB (in air) at 2.8 cm coil separation, which translates to 0.76%/759 μW and 0.6%/604 μW of power transfer efficiency (PTE) / power delivered to a 9 kΩ load (PDL), in body and air, respectively. A mock-up FF-WINeR is implemented to explore microassembly method of the 1×1 mm2 micromachined silicon die with a bonding wire-wound coil and a tungsten micro-wire electrode. Circuit design methods to fit the active circuitry in only 0.96 mm2 of die area in a 130 nm standard CMOS process, and satisfy the strict power and performance requirements (in simulations) are discussed.

A 32-site neural recording probe fabricated by DRIE of SOI substrates

An all-dry silicon-etch based micromachining process for neural probes was demonstrated in the manufacture of a probe with a 32-site recording electrode array. The fork-like probe shafts were formed by double-sided deep reactive ion etching (DRIE) of a silicon-on-insulator (SOI) substrate, with the buried SiO2 layer acting as an etch stop. The shafts typically had the dimensions 5 mm × 25 μm × 20 μm and ended in chisel-shaped tips with lateral taper angles of 4°. An array of Ir electrodes, each 100 μm2, and Au conductor traces were formed on top of the shafts by e-beam evaporation. An accompanying interconnect solution based on flexible printed circuitry was designed, enabling precise and flexible positioning of the probes in neural tissue. SEM studies showed sharply defined probes and probe tips. The electrical yield and function were verified in bench-top measurements in saline. The magnitude of the electrode impedance was in the 1 MΩ range at 1 kHz, which is consistent with neurophysiological recordings.