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Azees AA, Thompson AC, Ruther P, Ajay EA, Zhou J, Aregueta Robles UA, Garrett DJ, Quigley A, Fallon JB, Richardson RT. Spatially precise activation of the mouse cochlea with a multi-channel hybrid cochlear implant. J Neural Eng 2025; 22:036005. [PMID: 40273935 DOI: 10.1088/1741-2552/add091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2024] [Accepted: 04/24/2025] [Indexed: 04/26/2025]
Abstract
Objective.Cochlear implants are among the few clinical interventions for people with severe or profound hearing loss. However, current spread during monopolar electrical stimulation results in poor spectral resolution, prompting the exploration of optical stimulation as an alternative approach. Enabled by introducing light-sensitive ion channels into auditory neurons (optogenetics), optical stimulation has been shown to activate a more discrete neural area with minimal overlap between each frequency channel during simultaneous stimulation. However, the utility of optogenetic approaches is uncertain due to the low fidelity of responses to light and high-power requirements compared to electrical stimulation.Approach.Hybrid stimulation, combining sub-threshold electrical and optical pulses, has been shown to improve fidelity and use less light, but the impact on spread of activation and channel summation using a translatable, multi-channel hybrid implant is unknown. This study examined these factors during single channel and simultaneous multi-channel hybrid stimulation in transgenic mice expressing the ChR2/H134R opsin. Acutely deafened mice were implanted with a hybrid cochlear array containing alternating light emitting diodes and platinum electrode rings. Spiking activity in the inferior colliculus was recorded during electrical-only or hybrid stimulation in which optical and electrical stimuli were both at sub-threshold intensities. Thresholds, spread of activation, and threshold shifts during simultaneous hybrid stimulation were compared to electrical-only stimulation.Main results.The electrical current required to reach activation threshold during hybrid stimulation was reduced by 7.3 dB compared to electrical-only stimulation (p< 0.001). The activation width measured at two levels of discrimination above threshold and channel summation during simultaneous hybrid stimulation were significantly lower compared to electrical-only stimulation (p< 0.05), but there was no spatial advantage of hybrid stimulation at higher electrical stimulation levels.Significance.Reduced channel interaction would facilitate multi-channel simultaneous stimulation, thereby enhancing the perception of temporal fine structure which is crucial for music and speech in noise.
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Affiliation(s)
- Ajmal A Azees
- The Bionics Institute, Fitzroy, VIC 3065, Australia
- Department of Biomedical Engineering, RMIT University, Melbourne, VIC 3000, Australia
| | - Alex C Thompson
- The Bionics Institute, Fitzroy, VIC 3065, Australia
- Medical Bionics Department, University of Melbourne, East Melbourne, VIC, Australia
| | - Patrick Ruther
- Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg, Germany
- BrainLinks-BrainTools Center, University of Freiburg, 79110 Freiburg, Germany
| | - Elise A Ajay
- The Bionics Institute, Fitzroy, VIC 3065, Australia
- Faculty of Engineering and Information Technology, University of Melbourne, Melbourne, VIC, Australia
| | - Jenny Zhou
- The Bionics Institute, Fitzroy, VIC 3065, Australia
| | - Ulises A Aregueta Robles
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW 2033, Australia
| | - David J Garrett
- Department of Biomedical Engineering, RMIT University, Melbourne, VIC 3000, Australia
| | - Anita Quigley
- Department of Biomedical Engineering, RMIT University, Melbourne, VIC 3000, Australia
- St Vincent's Hospital Melbourne, Aikenhead Centre for Medical Discovery, Fitzroy, Melbourne, VIC 3065, Australia
- St. Vincent's Hospital Melbourne, Centre for Clinical Neurosciences and Neurological Research, Fitzroy, Melbourne, VIC 3065, Australia
- Department of Medicine, St Vincent's Hospital Melbourne, The University of Melbourne, Fitzroy, Melbourne, VIC 3065, Australia
| | - James B Fallon
- The Bionics Institute, Fitzroy, VIC 3065, Australia
- Department of Surgery (Otolaryngology), University of Melbourne, The Royal Victorian Eye and Ear Hospital, East Melbourne, VIC 3002, Australia
- Medical Bionics Department, University of Melbourne, East Melbourne, VIC, Australia
| | - Rachael T Richardson
- The Bionics Institute, Fitzroy, VIC 3065, Australia
- Medical Bionics Department, University of Melbourne, East Melbourne, VIC, Australia
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Ajay EA, Thompson AC, Azees AA, Wise AK, Grayden DB, Fallon JB, Richardson RT. Combined-electrical optogenetic stimulation but not channelrhodopsin kinetics improves the fidelity of high rate stimulation in the auditory pathway in mice. Sci Rep 2024; 14:21028. [PMID: 39251630 PMCID: PMC11385946 DOI: 10.1038/s41598-024-71712-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Accepted: 08/30/2024] [Indexed: 09/11/2024] Open
Abstract
Novel stimulation methods are needed to overcome the limitations of contemporary cochlear implants. Optogenetics is a technique that confers light sensitivity to neurons via the genetic introduction of light-sensitive ion channels. By controlling neural activity with light, auditory neurons can be activated with higher spatial precision. Understanding the behaviour of opsins at high stimulation rates is an important step towards their translation. To elucidate this, we compared the temporal characteristics of auditory nerve and inferior colliculus responses to optogenetic, electrical, and combined optogenetic-electrical stimulation in virally transduced mice expressing one of two channelrhodopsins, ChR2-H134R or ChIEF, at stimulation rates up to 400 pulses per second (pps). At 100 pps, optogenetic responses in ChIEF mice demonstrated higher fidelity, less change in latency, and greater response stability compared to responses in ChR2-H134R mice, but not at higher rates. Combined stimulation improved the response characteristics in both cohorts at 400 pps, although there was no consistent facilitation of electrical responses. Despite these results, day-long stimulation (up to 13 h) led to severe and non-recoverable deterioration of the optogenetic responses. The results of this study have significant implications for the translation of optogenetic-only and combined stimulation techniques for hearing loss.
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Affiliation(s)
- Elise A Ajay
- Bionics Institute, Melbourne, Australia
- Department of Biomedical Engineering and Graeme Clark Institute, University of Melbourne, Melbourne, Australia
| | - Alex C Thompson
- Bionics Institute, Melbourne, Australia
- Department of Medical Bionics, University of Melbourne, Melbourne, Australia
| | - Ajmal A Azees
- Bionics Institute, Melbourne, Australia
- Department of Electrical and Biomedical Engineering, RMIT, Melbourne, Australia
| | - Andrew K Wise
- Bionics Institute, Melbourne, Australia
- Department of Medical Bionics, University of Melbourne, Melbourne, Australia
| | - David B Grayden
- Bionics Institute, Melbourne, Australia
- Department of Biomedical Engineering and Graeme Clark Institute, University of Melbourne, Melbourne, Australia
| | - James B Fallon
- Bionics Institute, Melbourne, Australia
- Department of Medical Bionics, University of Melbourne, Melbourne, Australia
| | - Rachael T Richardson
- Bionics Institute, Melbourne, Australia.
- Department of Medical Bionics, University of Melbourne, Melbourne, Australia.
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Mu H, Smith D, Ng SH, Anand V, Le NHA, Dharmavarapu R, Khajehsaeidimahabadi Z, Richardson RT, Ruther P, Stoddart PR, Gricius H, Baravykas T, Gailevičius D, Seniutinas G, Katkus T, Juodkazis S. Fraxicon for Optical Applications with Aperture ∼1 mm: Characterisation Study. NANOMATERIALS (BASEL, SWITZERLAND) 2024; 14:287. [PMID: 38334558 PMCID: PMC10856946 DOI: 10.3390/nano14030287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2023] [Revised: 12/19/2023] [Accepted: 01/22/2024] [Indexed: 02/10/2024]
Abstract
Emerging applications of optical technologies are driving the development of miniaturised light sources, which in turn require the fabrication of matching micro-optical elements with sub-1 mm cross-sections and high optical quality. This is particularly challenging for spatially constrained biomedical applications where reduced dimensionality is required, such as endoscopy, optogenetics, or optical implants. Planarisation of a lens by the Fresnel lens approach was adapted for a conical lens (axicon) and was made by direct femtosecond 780 nm/100 fs laser writing in the SZ2080™ polymer with a photo-initiator. Optical characterisation of the positive and negative fraxicons is presented. Numerical modelling of fraxicon optical performance under illumination by incoherent and spatially extended light sources is compared with the ideal case of plane-wave illumination. Considering the potential for rapid replication in soft polymers and resists, this approach holds great promise for the most demanding technological applications.
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Affiliation(s)
- Haoran Mu
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
| | - Daniel Smith
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
| | - Soon Hock Ng
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
- Melbourne Centre for Nanofabrication, Australian National Fabrication Facility, Clayton, VIC 3168, Australia
| | - Vijayakumar Anand
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
- Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia
| | - Nguyen Hoai An Le
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
| | - Raghu Dharmavarapu
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
| | - Zahra Khajehsaeidimahabadi
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
| | - Rachael T. Richardson
- Bionics Institute, East Melbourne, VIC 3002, Australia;
- Medical Bionics Department, University of Melbourne, Fitzroy, VIC 3065, Australia
| | - Patrick Ruther
- Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany;
- BrainLinks-BrainTools Center, University of Freiburg, 79110 Freiburg im Breisgau, Germany
| | - Paul R. Stoddart
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
| | - Henrikas Gricius
- Laser Research Center, Physics Faculty, Vilnius University, Sauletekio Ave. 10, 10223 Vilnius, Lithuania; (H.G.); (D.G.)
| | | | - Darius Gailevičius
- Laser Research Center, Physics Faculty, Vilnius University, Sauletekio Ave. 10, 10223 Vilnius, Lithuania; (H.G.); (D.G.)
| | - Gediminas Seniutinas
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
- Melbourne Centre for Nanofabrication, Australian National Fabrication Facility, Clayton, VIC 3168, Australia
| | - Tomas Katkus
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
| | - Saulius Juodkazis
- Optical Sciences Centre, ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia; (H.M.); (D.S.); (N.H.A.L.); (R.D.); (Z.K.); (P.R.S.); (G.S.); (T.K.); (S.J.)
- Laser Research Center, Physics Faculty, Vilnius University, Sauletekio Ave. 10, 10223 Vilnius, Lithuania; (H.G.); (D.G.)
- WRH Program International Research Frontiers Initiative (IRFI) Tokyo Institute of Technology, Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
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