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A Molecular Perspective on Understanding and Modulating the Performance of Chronic Central Nervous System (CNS) Recording Electrodes.


In: Reichert WM, editor.


Indwelling Neural Implants: Strategies for Contending with the In Vivo Environment. Boca Raton (FL): CRC Press/Taylor & Francis; 2008. Chapter 6.


Successfully interfacing the CNS with external electronics holds great potential in improving the quality of life for patients with sensory and motor dysfunctions. The impact is already evident in the profound clinical applications of cochlear implants and deep brain stimulations [1,2]. More recently, the use of an invasive electronic brain implant, also known as a neuromotor prosthesis, to help a patient paralyzed by a tetraplegic spinal cord injury has been reported [3]. In the study, a 96-electrode array was implanted into the patient’s motor cortex to establish a brain–computer interface, where the patient could move a cursor to issue different instructions by thoughts of such motions. Clearly, it adds credibility to the enormous benefits that the interface technology could bring as a potential new therapy to restore independence for those severely disabled patients. Additionally, this interface technology may have significant implications for fundamental studies in neuroscience to understand normal physiology, pathology, or treatment of disorders such as epilepsy. A key component in such interface technology is the electrode, which is usually placed inside the CNS tissue to record neural impulses. These “spikes” will subsequently be translated into commands for external electronic devices. Currently, several types of electrodes are being used for research purposes, including microwires [4], glass electrodes [5], polymeric electrodes [6], and silicon micromachined implants [7,8]. Among these designs, microwires and silicon electrodes are the most popular. Microwires are well-established, metal-based, tip-recording electrodes. Their features include the ability to record large numbers of single units and ease of fabrication. However, they lack precise positioning inside the tissue. In comparison, silicon micromachined electrodes allow for greater control over electrode placement in vivo, as well as precise and versatile electrode design to accommodate signal recordings at different depths. This, however, comes at the price of a sophisticated multistep fabrication process. There are two prominent silicon electrodes in the field, widely known as the Utah electrode array (UEA) and the Michigan probe. The UEA is a three-dimensional array of needle-like structures with recording sites located at the tips, while the Michigan probe is a thin-film planar array with recording sites spaced out along the electrode shank. Our discussion will mainly refer to the silicon electrode, as such technology has the potential to enable precise dense sampling that will permit detailed mapping of the nervous system and improve the development of prosthetic devices.

Copyright © 2008, Taylor & Francis Group, LLC.

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