Farah Laiwalla

Listening to Brain Microcircuits for Interfacing With External World—Progress in Wireless Implantable Microelectronic Neuroengineering Devices

Acquiring neural signals at high spatial and temporal resolution directly from brain microcircuits and decoding their activity to interpret commands and/or prior planning activity, such as motion of an arm or a leg, is a prime goal of modern neurotechnology. Its practical aims include assistive devices for subjects whose normal neural information pathways are not functioning due to physical damage or disease. On the fundamental side, researchers are striving to decipher the code of multiple neural microcircuits which collectively make up natures amazing computing machine, the brain. By implanting biocompatible neural sensor probes directly into the brain, in the form of microelectrode arrays, it is now possible to extract information from interacting populations of neural cells with spatial and temporal resolution at the single cell level. With parallel advances in application of statistical and mathematical techniques tools for deciphering the neural code, extracted populations or correlated neurons, significant understanding has been achieved of those brain commands that control, e.g., the motion of an arm in a primate (monkey or a human subject). These developments are accelerating the work on neural prosthetics where brain derived signals may be employed to bypass, e.g., an injured spinal cord. One key element in achieving the goals for practical and versatile neural prostheses is the development of fully implantable wireless microelectronic ¿brain-interfaces¿ within the body, a point of special emphasis of this paper.

Active Microelectronic Neurosensor Arrays for Implantable Brain Communication Interfaces

We have built a wireless implantable microelectronic device for transmitting cortical signals transcutaneously. The device is aimed at interfacing a cortical microelectrode array to an external computer for neural control applications. Our implantable microsystem enables 16-channel broadband neural recording in a nonhuman primate brain by converting these signals to a digital stream of infrared light pulses for transmission through the skin. The implantable unit employs a flexible polymer substrate onto which we have integrated ultra-low power amplification with analog multiplexing, an analog-to-digital converter, a low power digital controller chip, and infrared telemetry. The scalable 16-channel microsystem can employ any of several modalities of power supply, including radio frequency by induction, or infrared light via photovoltaic conversion. As of the time of this report, the implant has been tested as a subchronic unit in nonhuman primates (~ 1 month), yielding robust spike and broadband neural data on all available channels.

Wireless, high-bandwidth recordings from non-human primate motor cortex using a scalable 16-Ch implantable microsystem

A multitude of neuroengineering challenges exist today in creating practical, chronic multichannel neural recording systems for primate research and human clinical application. Specifically, a) the persistent wired connections limit patient mobility from the recording system, b) the transfer of high bandwidth signals to external (even distant) electronics normally forces premature data reduction, and c) the chronic susceptibility to infection due to the percutaneous nature of the implants all severely hinder the success of neural prosthetic systems. Here we detail one approach to overcome these limitations: an entirely implantable, wirelessly communicating, integrated neural recording microsystem, dubbed the Brain Implantable Chip (BIC).

A microelectrode array incorporating an optical waveguide device for stimulation and spatiotemporal electrical recording of neural activity

Targeted neural excitation coupled with simultaneous multineuron recording is desirable both for studying the real-time dynamics of neural circuits and for prospective clinical treatment of neurological diseases. Optical stimulation of genetically targeted neurons expressing the light sensitive channel protein Channelrhodopsin (ChR2) has recently been reported as a means for millisecond temporal control of neuronal spiking activity with cell-type selectivity. This offers the prospect of enabling local (cellular level) stimulation and the concomitant monitoring of neural activity by extracellular electrophysiological methods, both in the vicinity of and distant to the stimulation site. We report here a novel dual-modality hybrid device which consists of a tapered coaxial optical waveguide (“optrode”) directly integrated into a 100 element intra-cortical multi-electrode recording array. The dual-modality array device was used in ChR2 transfected mouse brain slices. Specifically, epileptiform events were reliably optically triggered by the optrode and their spatiotemporal patterns were simultaneously recorded by the multi-electrode array.

Optical control of neural activity by waveguide delivery in genetically targeted brain tissue

Genetically targeted neurons in brain expressing light sensitive channel Channelrhodopsin can be stimulated optically. We report a novel optical waveguide probe for simultaneous optical stimulation and electrical recording of neurons to modulate neural network behavior.

Implantable Wireless Cortical Recording Device for Primates

We report on the performance of a wireless, implantable, neural recording platform. A multitude of neuroengineering challenges exist today in creating practical, chronic multichannel neural recording systems for primate research and human clinical application. Specifically, a) the persistent wired connections limit patient mobility from the recording system, b) the transfer of high bandwidth signals to external (even distant) electronics normally forces premature data reduction, and c) the chronic susceptibility to infection due to the percutaneous nature of the implants all severely hinder the success of neural prosthetic systems. Here we detail a scalable 16-channel microsystem that can employ any of several modalities of power delivery (wire, radio frequency induction, and a photovoltaic energy converter) and data transmission (wire, and transcutaneous infrared laser transmission). Data is reported from a recent sub-chronic (~30 day) rhesus macaque MI implantation.