Material considerations for optical interfacing to the nervous system
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Introduction The use of light rather than electricity to probe and manipulate neural networks is a relatively new approach. Given the wide variety of interactions between tissue and various parts of the electromagnetic spectrum, from the infrared to the ultraviolet, photonic technologies are quickly finding applications in both clinical and experimental neuroscience. Applications span a wide range and include imaging of electrical activity in single cells and neuronal networks, neuronal stimulation, as well as alteration of molecular pathways and gene expression.1–3 In 2010, the journal Nature Methods declared one technique of optical neuronal stimulation, optogenetics, the method of the year, proclaiming that: “with the capacity to control cellular behaviors using light and genetically encoded light-sensitive proteins, optogenetics has opened new doors for experimentation across biological fields.”4 Apart from satisfying our scientific curiosity, a key motivation for the development of better neural interfaces is their potential for treatment of neurological disorders, particularly for restoration of lost function in vision, hearing, and limb movement, and for treating disorders such as Parkinson’s disease and epilepsy. In order to be used clinically, however, optical devices must be
safe, reliable, and robust. Here we review optical methods for probing neural networks and address the materials challenges that must be overcome before these interfaces are fully realized for therapeutic use.
Benefits of optical neural interfaces It is known that neuronal communication is electrochemical in nature, thus it is perhaps not intuitive why we should consider light as an alternative to electrophysiological methods, the gold standard for interfacing with the nervous system for over a century.5,6 We postulate that optical techniques may overcome some of the fundamental limitations of electrophysiology. The first problem is spatial selectivity. Electrodes cannot discriminate between different current sources, and therefore detect either point sources such as single cells or the averaged activity of neuronal populations. Similarly, fine control over the stimulated area is limited due to passive spread of current along the path of least resistance, which is dictated by tissue anisotropy. These problems can be solved by using a microelectrode array, which effectively discretizes the tissue into small compartments, but practical considerations, such as the invasive nature of the device and the large parallel hardware architecture
Mykyta M. Chernov, Department of Biomedical Engineering, Vanderbilt University, Nashville, TN; [email protected] Austin R. Duke, Department of Biomedical Engineering, Vanderbilt University, Nashville, TN; [email protected] Jonathan M. Cayce, Department of Biomedical Engineering, Vanderbilt University, Nashville, TN; [email protected] Spencer W. Crowder, Department of Biomedical Engineering, Vanderbilt University, Nashville, TN; [email protected] Hak-Joo
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