Adaptive Wireless Power Transfer and Backscatter Communication for Perpetual Operation of Wireless Brain-Computer Interfaces

Brain-computer interfaces (BCIs) are neural prosthetics that enable closed-loop electrophysiology procedures. These devices are currently used in fundamental neurophysiology research, and they are moving toward clinical viability for neural rehabilitation. State-of-the-art BCI experiments have often been performed using tethered (wired) setups in controlled laboratory settings. Wired tethers simplify power and data interfaces but restrict the duration and types of experiments that are possible, particularly for the study of sensorimotor pathways in freely behaving animals. To eliminate tethers, there is significant ongoing research to develop fully wireless BCIs having wireless uplink of broadband neural recordings and wireless recharging for long-duration deployment, but significant challenges persist. BCIs must deliver complex functionality while complying with tightly coupled constraints in size, weight, power, noise, and biocompatibility. In this article, we provide an overview of recent progress in wireless BCIs and a detailed presentation of two emerging technologies that are advancing the state of the art: ultralow-power wireless backscatter communication and adaptive inductive resonant (AIR) wireless power transfer (WPT).

Remotely Powered Wireless Cortical Implants for Brain-Machine Interfaces

Kanber Mithat Silay

Brain-machine interfaces hold promise for restoring basic functions such as movement or speech for severely disabled patients, as well as for controlling neuroprosthetic devices for amputees. One of the major challenges of clinically viable neuroprostheses for chronic use is the implementation of fully implantable recording devices for stable, long-term recordings over large populations of neurons. Recent progress in the microelectronics and MEMS technologies has enabled miniaturization of microelectrode arrays which can be used for recording the neural activity of the brain and for stimulating the neurons. Nevertheless, the demanding requirements of fully implantable recording devices necessitate the incorporation of other active components with the microelectrodes. The presence of the active components in the implant requires power to be delivered to the device. Transcutaneous wires are commonly used for this purpose as well as for communication with the outside world. However, these wires pose the risk of infection to the patient. Another common method of powering is to utilize batteries in the implant. Nevertheless, this method is not desirable as the batteries have to be replaced at the end of their lifetime with a surgical procedure. This thesis presents the development of a remotely powered wireless cortical neural interface system for brain-machine interface applications. In the scope of this work, firstly, the requirements and specifications of the system are analyzed to examine the limits of operation. In addition, the thermal impact of cortical implant operation in the head is investigated to determine the maximum allowable power consumption in the implant. In order to supply power to the active components in the cortical implant, a closed-loop inductive remote powering link operating from a single external battery is implemented. The closed-loop operation enables adaptive delivery of power depending on the implant activity. For improving the power efficiency of the link, a discrete optimization algorithm is developed to design the geometry of the power transmission coils. In addition, application specific integrated circuits are designed to enhance the overall performance of the system and to decrease the footprint of the implant electronics. Moreover, wireless data communication for cortical implants is discussed and a solution for coexistence of the power and data links is presented. For implanting the cortical recording device into the body, a two-body packaging topology is proposed to position the implant inside the cranial bone. With this topology, the performance of the cortical neural interface is significantly improved. The fabricated cortical implants with the two-body package are characterized in air and in vitro. The power transfer efficiency of the closed-loop remote powering link operating from a single supply is measured to be 10.6% in vitro for 10 mW power delivered to the implant load. Finally, the operation of the implant in vitro is validated for over five weeks.

EPFL2012

Substrate arrays of iridium oxide microelectrodes for in vitro neuronal interfacing

Shady Didier Gawad, Michele Giugliano, Marc Olivier Heuschkel, Henry Markram, Hywel Morgan, Philippe Renaud

The design of novel bidirectional interfaces for in vivo and in vitro nervous systems is an important step towards future functional neuroprosthetics. Small electrodes, structures and devices are necessary to achieve high-resolution and target-selectivity during stimulation and recording of neuronal networks, while significant charge transfer and large signal-to-noise ratio are required for accurate time resolution. In addition, the physical properties of the interface should remain stable across time, especially when chronic in vivo applications or in vitro long-term studies are considered, unless a procedure to actively compensate for degradation is provided. In this short report, we describe the use and fabrication of arrays of 120 planar microelectrodes (MEAs) of sputtered Iridium Oxide (IrOx). The effective surface area of individual microelectrodes is significantly increased using electrochemical activation, a procedure that may also be employed to restore the properties of the electrodes as required. The electrode activation results in a very low interface impedance, especially in the lower frequency domain, which was characterized by impedance spectroscopy. The increase in the roughness of the microelectrodes surface was imaged using digital holographic microscopy and electron microscopy. Aging of the activated electrodes was also investigated, comparing storage in saline with storage in air. Demonstration of concept was achieved by recording multiple single-unit spike activity in acute brain slice preparations of rat neocortex. Data suggests that extracellular recording of action potentials can be achieved with planar IrOx MEAs with good signal-to-noise ratios.

2009

The use of intracranial recordings to decode human language: Challenges and opportunities

Stéphanie Martin

Decoding speech from intracranial recordings serves two main purposes: understanding the neural correlates of speech processing and decoding speech features for targeting speech neuroprosthetic devices. Intracranial recordings have high spatial and temporal resolution, and thus offer a unique opportunity to investigate and decode the electrophysiological dynamics underlying speech processing. In this review article, we describe current approaches to decoding different features of speech perception and production – such as spectrotemporal, phonetic, phonotactic, semantic, and articulatory components – using intracranial recordings. A specific section is devoted to the decoding of imagined speech, and potential applications to speech prosthetic devices. We outline the challenges in decoding human language, as well as the opportunities in scientific and neuroengineering applications.

Elsevier2016

Remotely Powered Wireless Cortical Implants for Brain-Machine Interfaces

Kanber Mithat Silay

EPFL2012