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Development of an Optogenetic Sensory Peripheral Nerve Interface
Sahil K. Kapur, MD1, Thomas Richner, MS2, Sarah Brodnick, BA2, Justin C. Williams, PhD2, Samuel O. Poore, MD, PhD1.
1UNIVERSITY OF WISCONSIN, MADISON, Madison, WI, USA, 2UNIVERSITY OF WISCONSIN MADISON, Madison, WI, USA.
Improvement in afferent sensory feedback is the necessary next step in the development of functional neuroprostheses. While electrical stimulation serves as the standard of peripheral nerve manipulation, the use of light sensitive ion channels in optogenetic models could provide a sensitive and specific alternative for afferent signal generation. In this study, we demonstrate similarities between the cortical representation of afferent neural signals that have been generated by electrical and optical stimulation of peripheral nerves. Furthermore, we demonstrate the ability to generate afferent signals that retain cortical localization following transcutaneous optical and electrical peripheral nerve stimulation.
Flexible thin film microelectrode arrays were implanted over the sensorimotor cortex in optogenetically modified transgenic mice expressing channelrhodopsin (a blue light sensitive ion channel) in accordance with IACUC guidelines. Seven days following cortical implantation, peripheral nerve signals were generated under four different experimental conditions: electrical stimulation following surgical exposure of the sciatic and median nerves, optical stimulation following surgical exposure of the sciatic and median nerves, transcutaneous electrical stimulation of the sciatic and median nerves and transcutaneous optical stimulation of the sciatic and median nerves. Local field potentials were recorded by the implanted cortical electrode arrays during these sessions.
Cortical signals recorded by the multielectrode arrays were localized to regions of the hindlimb or forelimb cortex corresponding to the peripheral nerve being stimulated. Localization of the signal was preserved across both electrical and optical stimulation modalities (Figure 1). Furthermore, cortical signals maintained their localization during transcutaneous optical and electrical stimulation (Figure 2). Signal amplitudes varied proportionately with the amplitude and pulse width of peripheral nerve stimulation. Generation of consistent localized cortical signals via both electrical and optical stimulation was maintained in experiments carried out over a period of at least 5 days. Control experiments carried out on wild type mice produced similar results following electrical stimulation but no cortical signals following optical stimulation of the peripheral nerves.
Preserved similarity and localization of cortical signals following electrical and optical stimulation of peripheral nerves implies that ascending sensory information can be reliably transmitted to the brain via either electrical stimulation or optical pulses applied to peripheral nerves. Furthermore, the robust cortical response to transcutaneus optical and electrical stimulation permits the non-invasive manipulation of peripheral nerves. These results along with our previously demonstrated results open the possibility of developing neuroprostheses capable of generating afferent and efferent neural signals in response to optical stimulation.
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