Multichannel optrodes for photonic stimulation

Abstract

. An emerging method in the field of neural stimulation is the use of photons to activate neurons. The possible advantage of optical stimulation over electrical is attributable to its spatially selective activation of small neuron populations, which is promising in generating superior spatial resolution in neural interfaces. Two principal methods are explored for cochlear prostheses: direct stimulation of nerves with infrared light and optogenetics. This paper discusses basic requirements for developing a light delivery system (LDS) for the cochlea and provides examples for building such devices. The proposed device relies on small optical sources, which are assembled in an array to be inserted into the cochlea. The mechanical properties, the biocompatibility, and the efficacy of optrodes have been tested in animal models. The force required to insert optrodes into a model of the human scala tympani was comparable to insertion forces obtained for contemporary cochlear implant electrodes. Side-emitting diodes are powerful enough to evoke auditory responses in guinea pigs. Chronic implantation of the LDS did not elevate auditory brainstem responses over 26 weeks.

Infrared inhibition impacts on locally initiated and propagating action potentials and the downstream synaptic transmission

“…Infrared (IR) light has emerged as a new modality that can reliably modulate both neural and muscular activities with the advantages of being contact-free, spatially selective, and MRI compatible. 1 – 3 IR-mediated modulation of excitable tissues has been demonstrated in a wide range of promising clinical applications, such as cochlear prostheses, 4 , 5 brain stimulation and mapping, 6 – 9 cardiac pacing, 10 and neural monitoring during surgery. 11 , 12 The main biological processes induced by pulsed IR light are attributed to the spatiotemporal thermal transients generated by water and tissue absorption, 13 which in turn can alter the membrane capacitance, 14 – 17 membrane resistance, 18 , 19 ion channel activities, 19 – 25 and intracellular calcium dynamics.…”

Towards the optical cochlear implant: optogenetic approaches for hearing restoration

“…In a different study, an oCI housing 15 LEDs (1 × 0.6 mm; max. 34 mW at 470 nm) embedded in biocompatible silicone has been realized and implanted into a human scala tympani model with insertion forces comparable to commercially available eCIs (Xu et al , ). Besides application for cochlear optogenetics, wireless controllable LEDs with ultraviolet (100 × 100 μm), blue, green, yellow, and red (220 × 270 μm each) emission peaks have been developed for optogenetic stimulation of the central nervous system in vivo (Shin et al , ) , which might be utilized when developing oCIs for opsins with shifted peak action spectra in the future.…”

“…However, the coupling of light from an emitter into the fiber is more challenging than with multi‐mode fibers (Alt et al , ). Furthermore, polymer‐based waveguides which have been manufactured with core thicknesses below 10 μm offer an alternative approach, especially when considering mechanical properties, i.e., flexibility to wind along the cochlear spiral, and the number of independent stimulation channels, for which the waveguide dimensions are of critical importance (Zorzos et al , ; Alt et al , ; Xu et al , ). However, even state‐of‐the‐art polymer waveguides do not reach the outstanding light propagation of glass fibers.…”

The future of otology

“…In the future, neural stimulation may be photonic, in which arrays of minute light-emitting diodes control small groups of auditory neurons. 28 Hybrid devices, which electronically stimulate the high frequencies (basal turn) and maintain acoustic stimulation of the lower frequencies (more apical), are currently in development. If concerns over preservation of residual hearing are overcome, these hybrid devices are likely to find important use in presbyacusis and other high frequency sensory losses.…”