1
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Titchener SA, Nayagam DAX, Kvansakul J, Kolic M, Baglin EK, Abbott CJ, McGuinness MB, Ayton LN, Luu CD, Greenstein S, Kentler WG, Shivdasani MN, Allen PJ, Petoe MA. A Second-Generation (44-Channel) Suprachoroidal Retinal Prosthesis: Long-Term Observation of the Electrode-Tissue Interface. Transl Vis Sci Technol 2022; 11:12. [PMID: 35696133 PMCID: PMC9202334 DOI: 10.1167/tvst.11.6.12] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Purpose To report the long-term observations of the electrode–tissue interface and perceptual stability in humans after chronic stimulation with a 44-channel suprachoroidal retinal implant. Methods Four subjects (S1–4) with end-stage retinitis pigmentosa received the implant unilaterally (NCT03406416). Electrode impedances, electrode–retina distance (measured using optical coherence tomography imaging), and perceptual thresholds were monitored up to 181 weeks after implantation as the subjects used the prosthesis in the laboratory and in daily life. Stimulation charge density was limited to 32 µC/cm2 per phase. Results Electrode impedances were stable longitudinally. The electrode–retina distances increased after surgery and then stabilized, and were well-described by an asymptotic exponential model. The stabilization of electrode–retina distances was variable between subjects, stabilizing after 45 weeks for S1, 63 weeks for S2, and 24 weeks for S3 (linear regression; Pgradient > 0.05). For S4, a statistically significant increase in electrode–retina distance persisted (P < 0.05), but by the study end point the rate of increase was clinically insignificant (exponential model: 0.33 µm/wk). Perceptual electrical thresholds were stable in one subject, decreased over time in two subjects (linear model; P < 0.05), and increased slightly in one subject but remained within the predefined charge limits (P = 0.02). Conclusions Chronic stimulation with the suprachoroidal retinal prosthesis over 3 years resulted in stable impedances, small individual changes in perceptual electrical thresholds, and no clinically significant increase in electrode–retina distances after a period of settling after surgery. Translational Relevance Chronic stimulation with the 44-channel suprachoroidal retinal implant with a charge density of up to 32 µC/cm2 per phase is suitable for long-term use in humans.
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Affiliation(s)
- Samuel A Titchener
- Bionics Institute, East Melbourne, Victoria, Australia.,Medical Bionics Department, University of Melbourne, Melbourne, Victoria, Australia
| | - David A X Nayagam
- Bionics Institute, East Melbourne, Victoria, Australia.,Department of Pathology, University of Melbourne, Victoria, Australia.,Centre for Eye Research Australia, Royal Victorian Eye & Ear Hospital, Melbourne, Victoria, Australia
| | - Jessica Kvansakul
- Bionics Institute, East Melbourne, Victoria, Australia.,Medical Bionics Department, University of Melbourne, Melbourne, Victoria, Australia
| | - Maria Kolic
- Centre for Eye Research Australia, Royal Victorian Eye & Ear Hospital, Melbourne, Victoria, Australia
| | - Elizabeth K Baglin
- Centre for Eye Research Australia, Royal Victorian Eye & Ear Hospital, Melbourne, Victoria, Australia
| | - Carla J Abbott
- Centre for Eye Research Australia, Royal Victorian Eye & Ear Hospital, Melbourne, Victoria, Australia.,Ophthalmology, Department of Surgery, University of Melbourne, Melbourne, Victoria, Australia
| | - Myra B McGuinness
- Centre for Eye Research Australia, Royal Victorian Eye & Ear Hospital, Melbourne, Victoria, Australia.,Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Victoria, Australia
| | - Lauren N Ayton
- Centre for Eye Research Australia, Royal Victorian Eye & Ear Hospital, Melbourne, Victoria, Australia.,Ophthalmology, Department of Surgery, University of Melbourne, Melbourne, Victoria, Australia.,Department of Optometry and Vision Sciences, University of Melbourne, Melbourne, Victoria, Australia
| | - Chi D Luu
- Centre for Eye Research Australia, Royal Victorian Eye & Ear Hospital, Melbourne, Victoria, Australia.,Ophthalmology, Department of Surgery, University of Melbourne, Melbourne, Victoria, Australia
| | - Steven Greenstein
- Bionics Institute, East Melbourne, Victoria, Australia.,Department of Biomedical Engineering, University of Melbourne, Melbourne, Victoria, Australia
| | - William G Kentler
- Department of Biomedical Engineering, University of Melbourne, Melbourne, Victoria, Australia
| | - Mohit N Shivdasani
- Bionics Institute, East Melbourne, Victoria, Australia.,Graduate School of Biomedical Engineering, University of New South Wales, Kensington, NSW, Australia
| | - Penelope J Allen
- Centre for Eye Research Australia, Royal Victorian Eye & Ear Hospital, Melbourne, Victoria, Australia.,Ophthalmology, Department of Surgery, University of Melbourne, Melbourne, Victoria, Australia
| | - Matthew A Petoe
- Bionics Institute, East Melbourne, Victoria, Australia.,Medical Bionics Department, University of Melbourne, Melbourne, Victoria, Australia
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2
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Pietra G, Bonifacino T, Talamonti D, Bonanno G, Sale A, Galli L, Baroncelli L. Visual Cortex Engagement in Retinitis Pigmentosa. Int J Mol Sci 2021; 22:ijms22179412. [PMID: 34502320 PMCID: PMC8431500 DOI: 10.3390/ijms22179412] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 08/20/2021] [Accepted: 08/26/2021] [Indexed: 11/24/2022] Open
Abstract
Retinitis pigmentosa (RP) is a family of inherited disorders caused by the progressive degeneration of retinal photoreceptors. There is no cure for RP, but recent research advances have provided promising results from many clinical trials. All these therapeutic strategies are focused on preserving existing photoreceptors or substituting light-responsive elements. Vision recovery, however, strongly relies on the anatomical and functional integrity of the visual system beyond photoreceptors. Although the retinal structure and optic pathway are substantially preserved at least in early stages of RP, studies describing the visual cortex status are missing. Using a well-established mouse model of RP, we analyzed the response of visual cortical circuits to the progressive degeneration of photoreceptors. We demonstrated that the visual cortex goes through a transient and previously undescribed alteration in the local excitation/inhibition balance, with a net shift towards increased intracortical inhibition leading to improved filtering and decoding of corrupted visual inputs. These results suggest a compensatory action of the visual cortex that increases the range of residual visual sensitivity in RP.
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Affiliation(s)
- Gianluca Pietra
- Neuroscience Institute, National Research Council (CNR), I-56124 Pisa, Italy; (G.P.); (D.T.); (A.S.); (L.G.)
| | - Tiziana Bonifacino
- Section of Pharmacology and Toxicology Unit, Department of Pharmacy, University of Genova, I-16148 Genova, Italy; (T.B.); (G.B.)
| | - Davide Talamonti
- Neuroscience Institute, National Research Council (CNR), I-56124 Pisa, Italy; (G.P.); (D.T.); (A.S.); (L.G.)
- Department of Life Science, University of Trieste, I-34128 Trieste, Italy
| | - Giambattista Bonanno
- Section of Pharmacology and Toxicology Unit, Department of Pharmacy, University of Genova, I-16148 Genova, Italy; (T.B.); (G.B.)
- IRCCS Ospedale Policlinico San Martino, I-16132 Genova, Italy
| | - Alessandro Sale
- Neuroscience Institute, National Research Council (CNR), I-56124 Pisa, Italy; (G.P.); (D.T.); (A.S.); (L.G.)
| | - Lucia Galli
- Neuroscience Institute, National Research Council (CNR), I-56124 Pisa, Italy; (G.P.); (D.T.); (A.S.); (L.G.)
| | - Laura Baroncelli
- Neuroscience Institute, National Research Council (CNR), I-56124 Pisa, Italy; (G.P.); (D.T.); (A.S.); (L.G.)
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy
- Correspondence: ; Tel.: +39-503-153199; Fax: +39-503-153220
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3
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Pio-Lopez L, Poulkouras R, Depannemaecker D. Visual cortical prosthesis: an electrical perspective. J Med Eng Technol 2021; 45:394-407. [PMID: 33843427 DOI: 10.1080/03091902.2021.1907468] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The electrical stimulation of the visual cortices has the potential to restore vision to blind individuals. Until now, the results of visual cortical prosthetics have been limited as no prosthesis has restored a full working vision but the field has shown a renewed interest these last years, thanks to wireless and technological advances. However, several scientific and technical challenges are still open to achieve the therapeutic benefit expected by these new devices. One of the main challenges is the electrical stimulation of the brain itself. In this review, we analyse the results in electrode-based visual cortical prosthetics from the electrical point of view. We first describe what is known about the electrode-tissue interface and safety of electrical stimulation. Then we focus on the psychophysics of prosthetic vision and the state-of-the-art on the interplay between the electrical stimulation of the visual cortex and the phosphene perception. Lastly, we discuss the challenges and perspectives of visual cortex electrical stimulation and electrode array design to develop the new generation implantable cortical visual prostheses.
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Affiliation(s)
| | - Romanos Poulkouras
- Department of Bioelectronics, Ecole Nationale Supérieure des Mines, CMP-EMSE, Gardanne, France.,Institut de Neurosciences de la Timone, UMR 7289, CNRS, Aix-Marseille Université, Marseille, France
| | - Damien Depannemaecker
- Department of Integrative and Computational Neuroscience, Paris-Saclay Institute of Neuroscience, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France
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4
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Chenais NAL, Airaghi Leccardi MJI, Ghezzi D. Naturalistic spatiotemporal modulation of epiretinal stimulation increases the response persistence of retinal ganglion cell. J Neural Eng 2021; 18. [DOI: 10.1088/1741-2552/abcd6f] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Accepted: 11/24/2020] [Indexed: 12/24/2022]
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5
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Begenisic T, Mazziotti R, Sagona G, Lupori L, Sale A, Galli L, Baroncelli L. Preservation of Visual Cortex Plasticity in Retinitis Pigmentosa. Neuroscience 2020; 424:205-210. [PMID: 31901258 DOI: 10.1016/j.neuroscience.2019.10.045] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Revised: 10/07/2019] [Accepted: 10/27/2019] [Indexed: 02/07/2023]
Abstract
Retinitis Pigmentosa (RP) is a class of inherited disorders caused by the progressive death of photoreceptors in the retina. RP is still orphan of an effective treatment, with increasing optimism deriving from research aimed at arresting neurodegeneration or replacing light-responsive elements. All these therapeutic strategies rely on the functional integrity of the visual system downstream of photoreceptors. Whereas the inner retinal structure and optic radiation are known to be considerably preserved at least in early stages of RP, very little is known about the visual cortex. Remarkably, it remains completely unclear whether visual cortex plasticity is still present in RP. Using a well-established murine model of RP, the rd10 mouse, we report that visual cortical circuits retain high levels of plasticity, preserving their capability of input-dependent remodelling even at a late stage of retinal degeneration.
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Affiliation(s)
- Tatjana Begenisic
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy
| | - Raffaele Mazziotti
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; Department of Neuroscience, Psychology, Drug Research and Child Health NEUROFARBA, University of Florence, I-50135 Florence, Italy
| | - Giulia Sagona
- Department of Neuroscience, Psychology, Drug Research and Child Health NEUROFARBA, University of Florence, I-50135 Florence, Italy; Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy
| | - Leonardo Lupori
- BIO@SNS lab, Scuola Normale Superiore di Pisa, I-56125 Pisa, Italy
| | - Alessandro Sale
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy
| | - Lucia Galli
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy
| | - Laura Baroncelli
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy.
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6
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Baroncelli L, Lunghi C. Neuroplasticity of the visual cortex: in sickness and in health. Exp Neurol 2020; 335:113515. [PMID: 33132181 DOI: 10.1016/j.expneurol.2020.113515] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 10/14/2020] [Accepted: 10/21/2020] [Indexed: 01/18/2023]
Abstract
Brain plasticity refers to the ability of synaptic connections to adapt their function and structure in response to experience, including environmental changes, sensory deprivation and injuries. Plasticity is a distinctive, but not exclusive, property of the developing nervous system. This review introduces the concept of neuroplasticity and describes classic paradigms to illustrate cellular and molecular mechanisms underlying synapse modifiability. Then, we summarize a growing number of studies showing that the adult cerebral cortex retains a significant degree of plasticity highlighting how the identification of strategies to enhance the plastic potential of the adult brain could pave the way for the development of novel therapeutic approaches aimed at treating amblyopia and other neurodevelopmental disorders. Finally, we analyze how the visual system adjusts to neurodegenerative conditions leading to blindness and we discuss the crucial role of spared plasticity in the visual system for sight recovery.
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Affiliation(s)
- Laura Baroncelli
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy.
| | - Claudia Lunghi
- Laboratoire des systèmes perceptifs, Département d'études cognitives, École normale supérieure, PSL University, CNRS, 75005 Paris, France
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7
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Zhang X, Ma Z, Zheng H, Li T, Chen K, Wang X, Liu C, Xu L, Wu X, Lin D, Lin H. The combination of brain-computer interfaces and artificial intelligence: applications and challenges. ANNALS OF TRANSLATIONAL MEDICINE 2020; 8:712. [PMID: 32617332 PMCID: PMC7327323 DOI: 10.21037/atm.2019.11.109] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Brain-computer interfaces (BCIs) have shown great prospects as real-time bidirectional links between living brains and actuators. Artificial intelligence (AI), which can advance the analysis and decoding of neural activity, has turbocharged the field of BCIs. Over the past decade, a wide range of BCI applications with AI assistance have emerged. These "smart" BCIs including motor and sensory BCIs have shown notable clinical success, improved the quality of paralyzed patients' lives, expanded the athletic ability of common people and accelerated the evolution of robots and neurophysiological discoveries. However, despite technological improvements, challenges remain with regard to the long training periods, real-time feedback, and monitoring of BCIs. In this article, the authors review the current state of AI as applied to BCIs and describe advances in BCI applications, their challenges and where they could be headed in the future.
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Affiliation(s)
- Xiayin Zhang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China
| | - Ziyue Ma
- Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China
| | - Huaijin Zheng
- Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China
| | - Tongkeng Li
- Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China
| | - Kexin Chen
- Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China
| | - Xun Wang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China
| | - Chenting Liu
- Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China
| | - Linxi Xu
- Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China
| | - Xiaohang Wu
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China
| | - Duoru Lin
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China
| | - Haotian Lin
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China.,Center of Precision Medicine, Sun Yat-sen University, Guangzhou, China
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8
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Paraskevoudi N, Pezaris JS. Eye Movement Compensation and Spatial Updating in Visual Prosthetics: Mechanisms, Limitations and Future Directions. Front Syst Neurosci 2019; 12:73. [PMID: 30774585 PMCID: PMC6368147 DOI: 10.3389/fnsys.2018.00073] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Accepted: 12/21/2018] [Indexed: 01/01/2023] Open
Abstract
Despite appearing automatic and effortless, perceiving the visual world is a highly complex process that depends on intact visual and oculomotor function. Understanding the mechanisms underlying spatial updating (i.e., gaze contingency) represents an important, yet unresolved issue in the fields of visual perception and cognitive neuroscience. Many questions regarding the processes involved in updating visual information as a function of the movements of the eyes are still open for research. Beyond its importance for basic research, gaze contingency represents a challenge for visual prosthetics as well. While most artificial vision studies acknowledge its importance in providing accurate visual percepts to the blind implanted patients, the majority of the current devices do not compensate for gaze position. To-date, artificial percepts to the blind population have been provided either by intraocular light-sensing circuitry or by using external cameras. While the former commonly accounts for gaze shifts, the latter requires the use of eye-tracking or similar technology in order to deliver percepts based on gaze position. Inspired by the need to overcome the hurdle of gaze contingency in artificial vision, we aim to provide a thorough overview of the research addressing the neural underpinnings of eye compensation, as well as its relevance in visual prosthetics. The present review outlines what is currently known about the mechanisms underlying spatial updating and reviews the attempts of current visual prosthetic devices to overcome the hurdle of gaze contingency. We discuss the limitations of the current devices and highlight the need to use eye-tracking methodology in order to introduce gaze-contingent information to visual prosthetics.
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Affiliation(s)
- Nadia Paraskevoudi
- Brainlab – Cognitive Neuroscience Research Group, Department of Clinical Psychology and Psychobiology, University of Barcelona, Barcelona, Spain
- Institute of Neurosciences, University of Barcelona, Barcelona, Spain
| | - John S. Pezaris
- Department of Neurosurgery, Massachusetts General Hospital, Boston, MA, United States
- Department of Neurosurgery, Harvard Medical School, Boston, MA, United States
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9
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Bareket L, Barriga-Rivera A, Zapf MP, Lovell NH, Suaning GJ. Progress in artificial vision through suprachoroidal retinal implants. J Neural Eng 2018; 14:045002. [PMID: 28541930 DOI: 10.1088/1741-2552/aa6cbb] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Retinal implants have proven their ability to restore visual sensation to people with degenerative retinopathy, characterized by photoreceptor cell death and the retina's inability to sense light. Retinal bionics operate by electrically stimulating the surviving neurons in the retina, thus triggering the transfer of visual sensory information to the brain. Suprachoroidal implants were first investigated in Australia in the 1950s. In this approach, the neuromodulation hardware is positioned between the sclera and the choroid, thus providing significant surgical and safety benefits for patients, with the potential to maintain residual vision combined with the artificial input from the device. Here we review the latest advances and state of the art devices for suprachoroidal prostheses, highlight future technologies and discuss challenges and perspectives towards improved rehabilitation of vision.
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Affiliation(s)
- Lilach Bareket
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Australia
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10
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FitzGibbon T. Retinal prosthesis that incorporates the organization of the nerve fibre layer. Clin Exp Ophthalmol 2017; 45:401-408. [PMID: 28135031 DOI: 10.1111/ceo.12899] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Revised: 12/02/2016] [Accepted: 12/05/2016] [Indexed: 12/01/2022]
Abstract
Recent efforts to restore partial vision in blind patients have made significant progress. Currently, prosthetic design concentrates on stimulating as many foveal retinal ganglion cells as possible but is hampered by stimulation of the nerve fibre layer. This results in a nonvisuotopic arrangement of phosphenes (stimulation percepts). This article suggests that by extending the stimulation area well beyond the fovea and stimulating the nerve fibre layer, axons from any remaining ganglion cells in more peripheral regions of the retina (low acuity) can be used to generate a visuotopic map. Stimulation of the fibre layer will generate a large number of stimulation percepts; however, it is unlikely that these will have sufficient topographic order to be immediately useful to the patient. Thus, it will be necessary to recreate an ordered visuotopic map by using appropriate computer algorithms and interactions between the patient and the clinician.
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Affiliation(s)
- Thomas FitzGibbon
- Physiology Department, School of Medical Sciences, University of Sydney, Sydney, New South Wales, Australia
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11
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Lewis PM, Ayton LN, Guymer RH, Lowery AJ, Blamey PJ, Allen PJ, Luu CD, Rosenfeld JV. Advances in implantable bionic devices for blindness: a review. ANZ J Surg 2016; 86:654-9. [PMID: 27301783 PMCID: PMC5132139 DOI: 10.1111/ans.13616] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Revised: 03/03/2016] [Accepted: 03/17/2016] [Indexed: 02/02/2023]
Abstract
Since the 1950s, vision researchers have been working towards the ambitious goal of restoring a functional level of vision to the blind via electrical stimulation of the visual pathways. Groups based in Australia, USA, Germany, France and Japan report progress in the translation of retinal visual prosthetics from the experimental to clinical domains, with two retinal visual prostheses having recently received regulatory approval for clinical use. Regulatory approval for cortical visual prostheses is yet to be obtained; however, several groups report plans to conduct clinical trials in the near future, building upon the seminal clinical studies of Brindley and Dobelle. In this review, we discuss the general principles of visual prostheses employing electrical stimulation of the visual pathways, focusing on the retina and visual cortex as the two most extensively studied stimulation sites. We also discuss the surgical and functional outcomes reported to date for retinal and cortical prostheses, concluding with a brief discussion of novel developments in this field and an outlook for the future.
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Affiliation(s)
- Philip M Lewis
- Department of Neurosurgery, Alfred Hospital, Melbourne, Victoria, Australia.,Department of Surgery, Central Clinical School, Monash University, Melbourne, Victoria, Australia.,Monash Vision Group, Faculty of Engineering, Monash University, Melbourne, Victoria, Australia.,Monash Institute of Medical Engineering, Monash University, Melbourne, Victoria, Australia
| | - Lauren N Ayton
- Centre for Eye Research Australia, The Royal Victorian Eye and Ear Hospital, Melbourne, Victoria, Australia.,Department of Ophthalmology, The University of Melbourne, Melbourne, Victoria, Australia.,Department of Surgery, The University of Melbourne, Melbourne, Victoria, Australia
| | - Robyn H Guymer
- Centre for Eye Research Australia, The Royal Victorian Eye and Ear Hospital, Melbourne, Victoria, Australia.,Department of Ophthalmology, The University of Melbourne, Melbourne, Victoria, Australia.,Department of Surgery, The University of Melbourne, Melbourne, Victoria, Australia
| | - Arthur J Lowery
- Monash Vision Group, Faculty of Engineering, Monash University, Melbourne, Victoria, Australia.,Monash Institute of Medical Engineering, Monash University, Melbourne, Victoria, Australia
| | - Peter J Blamey
- Bionics Institute, Department of Medical Bionics, The University of Melbourne, Melbourne, Victoria, Australia
| | - Penelope J Allen
- Centre for Eye Research Australia, The Royal Victorian Eye and Ear Hospital, Melbourne, Victoria, Australia.,Department of Ophthalmology, The University of Melbourne, Melbourne, Victoria, Australia.,Department of Surgery, The University of Melbourne, Melbourne, Victoria, Australia
| | - Chi D Luu
- Centre for Eye Research Australia, The Royal Victorian Eye and Ear Hospital, Melbourne, Victoria, Australia.,Department of Ophthalmology, The University of Melbourne, Melbourne, Victoria, Australia.,Department of Surgery, The University of Melbourne, Melbourne, Victoria, Australia
| | - Jeffrey V Rosenfeld
- Department of Neurosurgery, Alfred Hospital, Melbourne, Victoria, Australia.,Department of Surgery, Central Clinical School, Monash University, Melbourne, Victoria, Australia.,Monash Vision Group, Faculty of Engineering, Monash University, Melbourne, Victoria, Australia.,Monash Institute of Medical Engineering, Monash University, Melbourne, Victoria, Australia.,F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland, USA
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12
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Yang F, Yang CH, Wang FM, Cheng YT, Teng CC, Lee LJ, Yang CH, Fan LS. A high-density microelectrode-tissue-microelectrode sandwich platform for application of retinal circuit study. Biomed Eng Online 2015; 14:109. [PMID: 26611649 PMCID: PMC4662037 DOI: 10.1186/s12938-015-0106-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 11/23/2015] [Indexed: 01/05/2023] Open
Abstract
Background Microelectrode array (MEA) devices are frequently used in neural circuit studies, especially in retinal prosthesis. For a high throughput stimulation and recording paradigm, it is desirable to obtain the responses of multiple surface RGCs initiated from the electrical signals delivered to multiple photoreceptor cells. This can be achieved by an high density MEA-tissue-MEA (MTM) sandwich configuration. However, the retina is one of the most metabolically active tissues, consumes oxygen as rapidly as the brain. The major concern of the MTM configuration is the supply of oxygen. Methods We aimed to develop a high density MTM sandwich platform which consists of stacks of a stimulation MEA, retinal tissue and a recording MEA. Retina is a metabolically active tissue and the firing rate is very sensitive to oxygen level. We designed, simulated and microfabricated porous high density MEAs and an adjustable perfusion system that electrical signals can be delivered to and recorded from the clipped retinal tissue. Results The porous high-density MEAs linked with stimulation or recording devices within a perfusion system were manufactured and the MTM platform was assembled with a retina slice inside. The firing rate remained constant between 25 and 55 min before dramatically declined, indicating that within certain period of time (e.g. 30 min after habituation), the retina condition was kept by sufficient oxygen supply via the perfusion holes in the MEAs provided by the double perfusion system. Conclusions MTM sandwich structure is an efficient platform to study the retinal neural circuit. The material and arrangement of high density microelectrodes with porous design make this MEA appropriate for sub-retina prosthesis. Finding ways to prolong the recording time and reduce the signal-to-noise ratio are important to improve our MTM prototype.
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Affiliation(s)
- Frank Yang
- Institute of NanoEngineering and Microsystems, National Tsing-Hua University, Hsin-Chu, Taiwan
| | - Chung-Hua Yang
- Institute of NanoEngineering and Microsystems, National Tsing-Hua University, Hsin-Chu, Taiwan
| | - Fu-Min Wang
- Institute of NanoEngineering and Microsystems, National Tsing-Hua University, Hsin-Chu, Taiwan
| | - Ya-Ting Cheng
- Institute of NanoEngineering and Microsystems, National Tsing-Hua University, Hsin-Chu, Taiwan
| | - Chih-Ciao Teng
- Institute of NanoEngineering and Microsystems, National Tsing-Hua University, Hsin-Chu, Taiwan
| | - Li-Jen Lee
- Graduated Institute of Anatomy and Cell Biology, National Taiwan University, Taipei, Taiwan
| | - Chang-Hao Yang
- Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan
| | - Long-Sheng Fan
- Institute of NanoEngineering and Microsystems, National Tsing-Hua University, Hsin-Chu, Taiwan.
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13
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Lewis PM, Rosenfeld JV. Electrical stimulation of the brain and the development of cortical visual prostheses: An historical perspective. Brain Res 2015; 1630:208-24. [PMID: 26348986 DOI: 10.1016/j.brainres.2015.08.038] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Accepted: 08/14/2015] [Indexed: 10/23/2022]
Abstract
Rapid advances are occurring in neural engineering, bionics and the brain-computer interface. These milestones have been underpinned by staggering advances in micro-electronics, computing, and wireless technology in the last three decades. Several cortically-based visual prosthetic devices are currently being developed, but pioneering advances with early implants were achieved by Brindley followed by Dobelle in the 1960s and 1970s. We have reviewed these discoveries within the historical context of the medical uses of electricity including attempts to cure blindness, the discovery of the visual cortex, and opportunities for cortex stimulation experiments during neurosurgery. Further advances were made possible with improvements in electrode design, greater understanding of cortical electrophysiology and miniaturisation of electronic components. Human trials of a new generation of prototype cortical visual prostheses for the blind are imminent. This article is part of a Special Issue entitled Hold Item.
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Affiliation(s)
- Philip M Lewis
- Monash Vision Group, Department of Electrical and Computer Systems Engineering, Monash University, Wellington Road, Clayton, VIC 3800, Australia; Department of Neurosurgery, Level 1 Old Baker Building, Alfred Hospital, 55 Commercial Road, Melbourne, VIC 3004, Australia; Department of Surgery, Monash University Central Clinical School, Level 6 Alfred Centre, 99 Commercial Road, Melbourne, VIC 3004, Australia; Monash Institute of Medical Engineering, Monash University, Wellington Road, Clayton, VIC 3800, Australia.
| | - Jeffrey V Rosenfeld
- Monash Vision Group, Department of Electrical and Computer Systems Engineering, Monash University, Wellington Road, Clayton, VIC 3800, Australia; Department of Neurosurgery, Level 1 Old Baker Building, Alfred Hospital, 55 Commercial Road, Melbourne, VIC 3004, Australia; Department of Surgery, Monash University Central Clinical School, Level 6 Alfred Centre, 99 Commercial Road, Melbourne, VIC 3004, Australia; Monash Institute of Medical Engineering, Monash University, Wellington Road, Clayton, VIC 3800, Australia; F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814, United States.
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Sorkin JA, Hughes S, Soares P, Popat KC. Titania nanotube arrays as interfaces for neural prostheses. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2015; 49:735-745. [PMID: 25687003 PMCID: PMC4331648 DOI: 10.1016/j.msec.2015.01.077] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 12/08/2014] [Accepted: 01/23/2015] [Indexed: 11/23/2022]
Abstract
Neural prostheses have become ever more acceptable treatments for many different types of neurological damage and disease. Here we investigate the use of two different morphologies of titania nanotube arrays as interfaces to advance the longevity and effectiveness of these prostheses. The nanotube arrays were characterized for their nanotopography, crystallinity, conductivity, wettability, surface mechanical properties and adsorption of key proteins: fibrinogen, albumin and laminin. The loosely packed nanotube arrays fabricated using a diethylene glycol based electrolyte, contained a higher presence of the anatase crystal phase and were subsequently more conductive. These arrays yielded surfaces with higher wettability and lower modulus than the densely packed nanotube arrays fabricated using water based electrolyte. Further the adhesion, proliferation and differentiation of the C17.2 neural stem cell line was investigated on the nanotube arrays. The proliferation ratio of the cells as well as the level of neuronal differentiation was seen to increase on the loosely packed arrays. The results indicate that loosely packed nanotube arrays similar to the ones produced here with a DEG based electrolyte, may provide a favorable template for growth and maintenance of C17.2 neural stem cell line.
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Affiliation(s)
- Jonathan A Sorkin
- Department of Mechanical Engineering, Colorado State University, Fort Collins CO 80523, USA
| | - Stephen Hughes
- Department of Chemical and Biological Engineering, Colorado State University, Fort Collins CO 80523, USA; School of Biomedical Engineering, Colorado State University, Fort Collins CO 80523, USA
| | - Paulo Soares
- Department of Mechanical Engineering, Polytechnic School, Pontifícia Universidade Católica do Paraná, Curitiba, PR 80215-901, Brazil
| | - Ketul C Popat
- Department of Mechanical Engineering, Colorado State University, Fort Collins CO 80523, USA; School of Biomedical Engineering, Colorado State University, Fort Collins CO 80523, USA.
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Thompson DM, Koppes AN, Hardy JG, Schmidt CE. Electrical stimuli in the central nervous system microenvironment. Annu Rev Biomed Eng 2015; 16:397-430. [PMID: 25014787 DOI: 10.1146/annurev-bioeng-121813-120655] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Electrical stimulation to manipulate the central nervous system (CNS) has been applied as early as the 1750s to produce visual sensations of light. Deep brain stimulation (DBS), cochlear implants, visual prosthetics, and functional electrical stimulation (FES) are being applied in the clinic to treat a wide array of neurological diseases, disorders, and injuries. This review describes the history of electrical stimulation of the CNS microenvironment; recent advances in electrical stimulation of the CNS, including DBS to treat essential tremor, Parkinson's disease, and depression; FES for the treatment of spinal cord injuries; and alternative electrical devices to restore vision and hearing via neuroprosthetics (retinal and cochlear implants). It also discusses the role of electrical cues during development and following injury and, importantly, manipulation of these endogenous cues to support regeneration of neural tissue.
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Affiliation(s)
- Deanna M Thompson
- Department of Biomedical Engineering and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180;
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Hadjinicolaou AE, Savage CO, Apollo NV, Garrett DJ, Cloherty SL, Ibbotson MR, O'Brien BJ. Optimizing the Electrical Stimulation of Retinal Ganglion Cells. IEEE Trans Neural Syst Rehabil Eng 2015; 23:169-78. [DOI: 10.1109/tnsre.2014.2361900] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Maghami MH, Sodagar AM, Lashay A, Riazi-Esfahani H, Riazi-Esfahani M. Visual prostheses: the enabling technology to give sight to the blind. J Ophthalmic Vis Res 2015; 9:494-505. [PMID: 25709777 PMCID: PMC4329712 DOI: 10.4103/2008-322x.150830] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2013] [Accepted: 03/02/2014] [Indexed: 11/08/2022] Open
Abstract
Millions of patients are either slowly losing their vision or are already blind due to retinal degenerative diseases such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD) or because of accidents or injuries. Employment of artificial means to treat extreme vision impairment has come closer to reality during the past few decades. Currently, many research groups work towards effective solutions to restore a rudimentary sense of vision to the blind. Aside from the efforts being put on replacing damaged parts of the retina by engineered living tissues or microfabricated photoreceptor arrays, implantable electronic microsystems, referred to as visual prostheses, are also sought as promising solutions to restore vision. From a functional point of view, visual prostheses receive image information from the outside world and deliver them to the natural visual system, enabling the subject to receive a meaningful perception of the image. This paper provides an overview of technical design aspects and clinical test results of visual prostheses, highlights past and recent progress in realizing chronic high-resolution visual implants as well as some technical challenges confronted when trying to enhance the functional quality of such devices.
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Affiliation(s)
- Mohammad Hossein Maghami
- Research Laboratory for Integrated Circuits and Systems (ICAS), Electrical Engineering Department, K.N. Toosi University of Technology, Tehran, Iran
| | - Amir Masoud Sodagar
- Research Laboratory for Integrated Circuits and Systems (ICAS), Electrical Engineering Department, K.N. Toosi University of Technology, Tehran, Iran ; Electrical Engineering Department, Polytechnique Montreal, Montreal, Quebec, Canada
| | - Alireza Lashay
- Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran
| | - Hamid Riazi-Esfahani
- Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran
| | - Mohammad Riazi-Esfahani
- Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran
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Choi CW, Kim PS, Shin SA, Yang JY, Yang YS. Lateral geniculate body evoked potentials elicited by visual and electrical stimulation. KOREAN JOURNAL OF OPHTHALMOLOGY 2014; 28:337-42. [PMID: 25120343 PMCID: PMC4120355 DOI: 10.3341/kjo.2014.28.4.337] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Accepted: 11/12/2013] [Indexed: 11/23/2022] Open
Abstract
PURPOSE Blind individuals who have photoreceptor loss are known to perceive phosphenes with electrical stimulation of their remaining retinal ganglion cells. We proposed that implantable lateral geniculate body (LGB) stimulus electrode arrays could be used to generate phosphene vision. We attempted to refine the basic reference of the electrical evoked potentials (EEPs) elicited by microelectrical stimulations of the optic nerve, optic tract and LGB of a domestic pig, and then compared it to visual evoked potentials (VEPs) elicited by short-flash stimuli. METHODS For visual function measurement, VEPs in response to short-flash stimuli on the left eye of the domestic pig were assessed over the visual cortex at position Oz with the reference electrode at Fz. After anesthesia, linearly configured platinum wire electrodes were inserted into the optic nerve, optic track and LGB. To determine the optimal stimulus current, EEPs were recorded repeatedly with controlling the pulse and power. The threshold of current and charge density to elicit EEPs at 0.3 ms pulse duration was about ±10 µA. RESULTS Our experimental results showed that visual cortex activity can be effectively evoked by stimulation of the optic nerve, optic tract and LGB using penetrating electrodes. The latency of P1 was more shortened as the electrical stimulation was closer to LGB. The EEPs of two-channel in the visual cortex demonstrated a similar pattern with stimulation of different spots of the stimulating electrodes. We found that the LGB-stimulated EEP pattern was very similar to the simultaneously generated VEP on the control side, although implicit time deferred. CONCLUSIONS EEPs and VEPs derived from visual-system stimulation were compared. The LGB-stimulated EEP wave demonstrated a similar pattern to the VEP waveform except implicit time, indicating prosthetic-based electrical stimulation of the LGB could be utilized for the blind to perceive vision of phosphenes.
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Affiliation(s)
- Chang Wook Choi
- Department of Ophthalmology, Wonkwang University Hospital, Wonkwang University School of Medicine, Iksan, Korea
| | - Pan Sang Kim
- Department of Ophthalmology, Wonkwang University Hospital, Wonkwang University School of Medicine, Iksan, Korea
| | - Sun Ae Shin
- Department of Ophthalmology, Wonkwang University Hospital, Wonkwang University School of Medicine, Iksan, Korea
| | - Ji Yeon Yang
- Hanson Institute, University of Adelaide, Adelaide, Australia
| | - Yun Sik Yang
- Department of Ophthalmology, Wonkwang University Hospital, Wonkwang University School of Medicine, Iksan, Korea
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Herreros I, Giovannucci A, Taub AH, Hogri R, Magal A, Bamford S, Prueckl R, Verschure PFMJ. A Cerebellar Neuroprosthetic System: Computational Architecture and in vivo Test. Front Bioeng Biotechnol 2014; 2:14. [PMID: 25152887 PMCID: PMC4126458 DOI: 10.3389/fbioe.2014.00014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Accepted: 05/04/2014] [Indexed: 11/13/2022] Open
Abstract
Emulating the input–output functions performed by a brain structure opens the possibility for developing neuroprosthetic systems that replace damaged neuronal circuits. Here, we demonstrate the feasibility of this approach by replacing the cerebellar circuit responsible for the acquisition and extinction of motor memories. Specifically, we show that a rat can undergo acquisition, retention, and extinction of the eye-blink reflex even though the biological circuit responsible for this task has been chemically inactivated via anesthesia. This is achieved by first developing a computational model of the cerebellar microcircuit involved in the acquisition of conditioned reflexes and training it with synthetic data generated based on physiological recordings. Secondly, the cerebellar model is interfaced with the brain of an anesthetized rat, connecting the model’s inputs and outputs to afferent and efferent cerebellar structures. As a result, we show that the anesthetized rat, equipped with our neuroprosthetic system, can be classically conditioned to the acquisition of an eye-blink response. However, non-stationarities in the recorded biological signals limit the performance of the cerebellar model. Thus, we introduce an updated cerebellar model and validate it with physiological recordings showing that learning becomes stable and reliable. The resulting system represents an important step toward replacing lost functions of the central nervous system via neuroprosthetics, obtained by integrating a synthetic circuit with the afferent and efferent pathways of a damaged brain region. These results also embody an early example of science-based medicine, where on the one hand the neuroprosthetic system directly validates a theory of cerebellar learning that informed the design of the system, and on the other one it takes a step toward the development of neuro-prostheses that could recover lost learning functions in animals and, in the longer term, humans.
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Affiliation(s)
- Ivan Herreros
- Synthetic Perceptive, Emotive and Cognitive Systems group (SPECS), Universitat Pompeu Fabra , Barcelona , Spain
| | - Andrea Giovannucci
- Synthetic Perceptive, Emotive and Cognitive Systems group (SPECS), Universitat Pompeu Fabra , Barcelona , Spain
| | - Aryeh H Taub
- Psychobiology Research Unit, Tel Aviv University , Tel Aviv , Israel
| | - Roni Hogri
- Psychobiology Research Unit, Tel Aviv University , Tel Aviv , Israel
| | - Ari Magal
- Psychobiology Research Unit, Tel Aviv University , Tel Aviv , Israel
| | - Sim Bamford
- Physics Laboratory, Istituto Superiore di Sanità , Rome , Italy
| | | | - Paul F M J Verschure
- Synthetic Perceptive, Emotive and Cognitive Systems group (SPECS), Universitat Pompeu Fabra , Barcelona , Spain ; Institució Catalana de Recerca i Estudis Avançats , Barcelona , Spain
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20
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A primer on brain-machine interfaces, concepts, and technology: a key element in the future of functional neurorestoration. World Neurosurg 2013; 79:457-71. [PMID: 23333985 DOI: 10.1016/j.wneu.2013.01.078] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Accepted: 01/14/2013] [Indexed: 11/23/2022]
Abstract
Conventionally, the practice of neurosurgery has been characterized by the removal of pathology, congenital or acquired. The emerging complement to the removal of pathology is surgery for the specific purpose of restoration of function. Advents in neuroscience, technology, and the understanding of neural circuitry are creating opportunities to intervene in disease processes in a reparative manner, thereby advancing toward the long-sought-after concept of neurorestoration. Approaching the issue of neurorestoration from a biomedical engineering perspective is the rapidly growing arena of implantable devices. Implantable devices are becoming more common in medicine and are making significant advancements to improve a patient's functional outcome. Devices such as deep brain stimulators, vagus nerve stimulators, and spinal cord stimulators are now becoming more commonplace in neurosurgery as we utilize our understanding of the nervous system to interpret neural activity and restore function. One of the most exciting prospects in neurosurgery is the technologically driven field of brain-machine interface, also known as brain-computer interface, or neuroprosthetics. The successful development of this technology will have far-reaching implications for patients suffering from a great number of diseases, including but not limited to spinal cord injury, paralysis, stroke, or loss of limb. This article provides an overview of the issues related to neurorestoration using implantable devices with a specific focus on brain-machine interface technology.
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21
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Mean retinal ganglion cell axon diameter varies with location in the human retina. Jpn J Ophthalmol 2012; 56:631-7. [DOI: 10.1007/s10384-012-0185-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2012] [Accepted: 08/06/2012] [Indexed: 10/27/2022]
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22
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Rattay F, Paredes L, Leao R. Strength-duration relationship for intra- versus extracellular stimulation with microelectrodes. Neuroscience 2012; 214:1-13. [PMID: 22516015 PMCID: PMC3401985 DOI: 10.1016/j.neuroscience.2012.04.004] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Revised: 03/06/2012] [Accepted: 04/05/2012] [Indexed: 12/04/2022]
Abstract
Chronaxie, a historically introduced excitability time parameter for electrical stimulation, has been assumed to be closely related to the time constant of the cell membrane. Therefore, it is perplexing that significantly larger chronaxies have been found for intracellular than for extracellular stimulation. Using compartmental model analysis, this controversy is explained on the basis that extracellular stimulation also generates hyperpolarized regions of the cell membrane hindering a steady excitation as seen in the intracellular case. The largest inside/outside chronaxie ratio for microelectrode stimulation is found in close vicinity of the cell. In the case of monophasic cathodic stimulation, the length of the primarily excited zone which is situated between the hyperpolarized regions increases with electrode-cell distance. For distant electrodes this results in an excitation process comparable to the temporal behavior of intracellular stimulation. Chronaxie also varies along the neural axis, being small for electrode positions at the nodes of Ranvier and axon initial segment and larger at the soma and dendrites. As spike initiation site can change for short and long pulses, in some cases strength-duration curves have a bimodal shape, and thus, they deviate from a classical monotonic curve as described by the formulas of Lapicque or Weiss.
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Affiliation(s)
- F. Rattay
- Institute for Analysis and Scientific Computing, Vienna University of Technology, A-1040 Vienna, Austria
| | - L.P. Paredes
- Institute for Analysis and Scientific Computing, Vienna University of Technology, A-1040 Vienna, Austria
| | - R.N. Leao
- Neurodynamics Laboratory, Department of Neuroscience, Uppsala University, Uppsala, Sweden
- Brain Institute, Federal University of Rio Grande do Norte, Natal-RN, Brazil
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23
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O’Doherty JE, Lebedev MA, Li Z, Nicolelis MA. Virtual active touch using randomly patterned intracortical microstimulation. IEEE Trans Neural Syst Rehabil Eng 2012; 20:85-93. [PMID: 22207642 PMCID: PMC3590844 DOI: 10.1109/tnsre.2011.2166807] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Intracortical microstimulation (ICMS) has promise as a means for delivering somatosensory feedback in neuroprosthetic systems. Various tactile sensations could be encoded by temporal, spatial, or spatiotemporal patterns of ICMS. However, the applicability of temporal patterns of ICMS to artificial tactile sensation during active exploration is unknown, as is the minimum discriminable difference between temporally modulated ICMS patterns. We trained rhesus monkeys in an active exploration task in which they discriminated periodic pulse-trains of ICMS (200 Hz bursts at a 10 Hz secondary frequency) from pulse trains with the same average pulse rate, but distorted periodicity (200 Hz bursts at a variable instantaneous secondary frequency). The statistics of the aperiodic pulse trains were drawn from a gamma distribution with mean inter-burst intervals equal to those of the periodic pulse trains. The monkeys distinguished periodic pulse trains from aperiodic pulse trains with coefficients of variation 0.25 or greater. Reconstruction of movement kinematics, extracted from the activity of neuronal populations recorded in the sensorimotor cortex concurrent with the delivery of ICMS feedback, improved when the recording intervals affected by ICMS artifacts were removed from analysis. These results add to the growing evidence that temporally patterned ICMS can be used to simulate a tactile sense for neuroprosthetic devices.
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Affiliation(s)
- Joseph E. O’Doherty
- Department of Neurobiology and the Center for Neuroengineering, Duke University, Durham, NC 27710 USA
| | - Mikhail A. Lebedev
- Department of Neurobiology and the Center for Neuroengineering, Duke University, Durham, NC 27710 USA
| | - Zheng Li
- Department of Neurobiology and the Center for Neuroengineering, Duke University, Durham, NC 27710 USA
| | - Miguel A.L. Nicolelis
- Departments of Neurobiology, Biomedical Engineering, Psychology, and the Center for Neuroengineering, Duke University, Durham, NC 27710 USA
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Cohen E, Agrawal A, Connors M, Hansen B, Charkhkar H, Pfefer J. Optical coherence tomography imaging of retinal damage in real time under a stimulus electrode. J Neural Eng 2011; 8:056017. [DOI: 10.1088/1741-2560/8/5/056017] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Panetsos F, Sanchez-Jimenez A, Rodrigo-Diaz E, Diaz-Guemes I, Sanchez FM. Consistent phosphenes generated by electrical microstimulation of the visual thalamus. An experimental approach for thalamic visual neuroprostheses. Front Neurosci 2011; 5:84. [PMID: 21779233 PMCID: PMC3132634 DOI: 10.3389/fnins.2011.00084] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2010] [Accepted: 06/10/2011] [Indexed: 11/24/2022] Open
Abstract
UNLABELLED Most work on visual prostheses has centered on developing retinal or cortical devices. However, when retinal implants are not feasible, neuroprostheses could be implanted in the lateral geniculate nucleus (LGN) of the thalamus, the intermediate relay station of visual information from the retina to the visual cortex (V1). The objective of the present study was to determine the types of artificial stimuli that when delivered to the visual thalamus can generate reliable responses of the cortical neurons similar to those obtained when the eye perceives a visual image. Visual stimuli {S(i)} were presented to one eye of an experimental animal and both, the thalamic {RTh(i)} and cortical responses {RV1(i)} to such stimuli were recorded. Electrical patterns {RTh(i)*} resembling {RTh(i)} were then injected into the visual thalamus to obtain cortical responses {RV1(i)*} similar to {RV1(i)}. Visually- and electrically generated V1 responses were compared. RESULTS During the course of this work we: (i) characterized the response of V1 neurons to visual stimuli according to response magnitude, duration, spiking rate, and the distribution of interspike intervals; (ii) experimentally tested the dependence of V1 responses on stimulation parameters such as intensity, frequency, duration, etc., and determined the ranges of these parameters generating the desired cortical activity; (iii) identified similarities between responses of V1 useful to compare the naturally and artificially generated neuronal activity of V1; and (iv) by modifying the stimulation parameters, we generated artificial V1 responses similar to those elicited by visual stimuli. Generation of predictable and consistent phosphenes by means of artificial stimulation of the LGN is important for the feasibility of visual prostheses. Here we proved that electrical stimuli to the LGN can generate V1 neural responses that resemble those elicited by natural visual stimuli.
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Affiliation(s)
- Fivos Panetsos
- Neurocomputing and Neurorobotics Research Group, Complutense University of MadridMadrid, Spain
- School of Optics, Complutense University of MadridMadrid, Spain
| | - Abel Sanchez-Jimenez
- Neurocomputing and Neurorobotics Research Group, Complutense University of MadridMadrid, Spain
- Faculty of Biology, Complutense University of MadridMadrid, Spain
| | - Elena Rodrigo-Diaz
- Neurocomputing and Neurorobotics Research Group, Complutense University of MadridMadrid, Spain
- School of Optics, Complutense University of MadridMadrid, Spain
| | - Idoia Diaz-Guemes
- Applied Research, “Jesus Uson” Minimally Invasive Surgery CentreCaceres, Spain
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Matthaei M, Zeitz O, Keserü M, Wagenfeld L, Hornig R, Post N, Richard G. Progress in the Development of Vision Prostheses. Ophthalmologica 2011; 225:187-92. [DOI: 10.1159/000318042] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Accepted: 01/15/2010] [Indexed: 11/19/2022]
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27
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Brugger D, Butovas S, Bogdan M, Schwarz C. Real-time adaptive microstimulation increases reliability of electrically evoked cortical potentials. IEEE Trans Biomed Eng 2011; 58:1483-91. [PMID: 21257369 DOI: 10.1109/tbme.2011.2107512] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Cortical neuroprostheses that employ repeated electrical stimulation of cortical areas with fixed stimulus parameters, are faced with the problem of large trial-by-trial variability of evoked potentials. This variability is caused by the ongoing cortical signal processing, but it is an unwanted phenomenon if one aims at imprinting neural activity as precisely as possible. Here, we use local field potentials measured by one microelectrode, located at a distance of 200 microns from the stimulation site, to drive the electrically evoked potential toward a desired target potential by real-time adaptation of the stimulus intensity. The functional relationship between ongoing cortical activity, evoked potential, and stimulus intensity was estimated by standard machine learning techniques (support vector regression with problem-specific kernel function) from a set of stimulation trials with randomly varied stimulus intensities. The smallest deviation from the target potential was achieved for low stimulus intensities. Further, the observed precision effect proved time sensitive, since it was abolished by introducing a delay between data acquisition and stimulation. These results indicate that local field potentials contain sufficient information about ongoing local signal processing to stabilize electrically evoked potentials. We anticipate that adaptive low intensity microstimulation will play an important role in future cortical prosthetic devices that aim at restoring lost sensory functions.
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Affiliation(s)
- Dominik Brugger
- Systems Neurophysiology Group, Werner Reichardt Centre for Integrative Neuroscience, University of Tübingen, Germany.
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Wang C, Bókkon I, Dai J, Antal I. Spontaneous and visible light-induced ultraweak photon emission from rat eyes. Brain Res 2011; 1369:1-9. [DOI: 10.1016/j.brainres.2010.10.077] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2010] [Revised: 10/15/2010] [Accepted: 10/19/2010] [Indexed: 11/30/2022]
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Abstract
Once the topic of folklore and science fiction, the notion of restoring vision to the blind is now approaching a tractable reality. Technological advances have inspired numerous multidisciplinary groups worldwide to develop visual neuroprosthetic devices that could potentially provide useful vision and improve the quality of life of profoundly blind individuals. While a variety of approaches and designs are being pursued, they all share a common principle of creating visual percepts through the stimulation of visual neural elements using appropriate patterns of electrical stimulation. Human clinical trials are now well underway and initial results have been met with a balance of excitement and cautious optimism. As remaining technical and surgical challenges continue to be solved and clinical trials move forward, we now enter a phase of development that requires careful consideration of a new set of issues. Establishing appropriate patient selection criteria, methods of evaluating long-term performance and effectiveness, and strategies to rehabilitate implanted patients will all need to be considered in order to achieve optimal outcomes and establish these devices as viable therapeutic options.
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Abstract
A phone survey was conducted with 80 visually impaired people in Turkey to understand what types of assistive products are used and to what extent. The perceived utility of selected products and reasons for nonuse were investigated. Descriptions of products that would be useful for the participants but may not be available on the market were also obtained. The three most used assistive products were found to be computer screen readers (46%), talking watches (26%), and screen readers for cellular phones (21%). Cellular phones with screen reading capability are the most desired assistive products among the visually impaired community, but their high cost is a major barrier. Most of the relevant technologies are available but some product development, such as adaptation to the Turkish language, is necessary. The three products most frequently requested are bus station/destination announcement systems, devices that warn the person about barriers, and devices that read printed documents and signs.
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Affiliation(s)
- Murat Bengisu
- Department of Industrial Design, Izmir University of Economics, Izmir, Turkey.
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McCreery D, Pikov V, Troyk PR. Neuronal loss due to prolonged controlled-current stimulation with chronically implanted microelectrodes in the cat cerebral cortex. J Neural Eng 2010; 7:036005. [PMID: 20460692 PMCID: PMC2921317 DOI: 10.1088/1741-2560/7/3/036005] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Activated iridium microelectrodes were implanted for 450-1282 days in the sensorimotor cortex of seven adult domestic cats and then pulsed for 240 h (8 h per day for 30 days) at 50 Hz. Continuous stimulation at 2 nC/phase and with a geometric charge density of 100 microC cm(-2) produced no detectable change in neuronal density in the tissue surrounding the microelectrode tips. However, pulsing with a continuous 100% duty cycle at 4 nC/phase and with a geometric charge density of 200 microC cm(-2) induced loss of cortical neurons over a radius of at least 150 microm from the electrode tips. The same stimulus regimen but with a duty cycle of 50% (1 s of stimulation, and then 1 s without stimulation repeated for 8 h) produced neuronal loss within a smaller radius, approximately 60 microm from the center of the electrode tips. However, there also was significant loss of neurons surrounding the unpulsed electrodes, presumably as a result of mechanical injury due to their insertion into and long-term residence in the tissue, and this was responsible for most of the neuronal loss within 150 microm of the electrodes pulsed with the 50% duty cycle.
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Affiliation(s)
- Douglas McCreery
- Neural Engineering Program, Huntington Medical Research Institutes, Pasadena, CA 91105, USA.
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Konrad P, Shanks T. Implantable brain computer interface: Challenges to neurotechnology translation. Neurobiol Dis 2010; 38:369-75. [DOI: 10.1016/j.nbd.2009.12.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2009] [Revised: 09/18/2009] [Accepted: 12/08/2009] [Indexed: 10/20/2022] Open
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Wang W, Collinger JL, Perez MA, Tyler-Kabara EC, Cohen LG, Birbaumer N, Brose SW, Schwartz AB, Boninger ML, Weber DJ. Neural interface technology for rehabilitation: exploiting and promoting neuroplasticity. Phys Med Rehabil Clin N Am 2010; 21:157-78. [PMID: 19951784 DOI: 10.1016/j.pmr.2009.07.003] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
This article reviews neural interface technology and its relationship with neuroplasticity. Two types of neural interface technology are reviewed, highlighting specific technologies that the authors directly work with: (1) neural interface technology for neural recording, such as the micro-ECoG BCI system for hand prosthesis control, and the comprehensive rehabilitation paradigm combining MEG-BCI, action observation, and motor imagery training; (2) neural interface technology for functional neural stimulation, such as somatosensory neural stimulation for restoring somatosensation, and non-invasive cortical stimulation using rTMS and tDCS for modulating cortical excitability and stroke rehabilitation. The close interaction between neural interface devices and neuroplasticity leads to increased efficacy of neural interface devices and improved functional recovery of the nervous system. This symbiotic relationship between neural interface technology and the nervous system is expected to maximize functional gain for individuals with various sensory, motor, and cognitive impairments, eventually leading to better quality of life.
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Affiliation(s)
- Wei Wang
- Department of Physical Medicine and Rehabilitation, University of Pittsburgh, 3471 Fifth Ave., Suite 202, Pittsburgh, PA 15213, USA
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ZHANG Y, KANETAKA H, SANO Y, KANO M, KUDO TA, SHIMIZU Y. MPC polymer regulates fibrous tissue formation by modulating cell adhesion to the biomaterial surface. Dent Mater J 2010; 29:518-28. [DOI: 10.4012/dmj.2009-138] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Nicolelis MAL, Lebedev MA. Principles of neural ensemble physiology underlying the operation of brain-machine interfaces. Nat Rev Neurosci 2009; 10:530-40. [PMID: 19543222 DOI: 10.1038/nrn2653] [Citation(s) in RCA: 232] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Research on brain-machine interfaces has been ongoing for at least a decade. During this period, simultaneous recordings of the extracellular electrical activity of hundreds of individual neurons have been used for direct, real-time control of various artificial devices. Brain-machine interfaces have also added greatly to our knowledge of the fundamental physiological principles governing the operation of large neural ensembles. Further understanding of these principles is likely to have a key role in the future development of neuroprosthetics for restoring mobility in severely paralysed patients.
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Affiliation(s)
- Miguel A L Nicolelis
- Duke University Center for Neuroengineering and the Department of Neurobiology, Duke University, Durham, North Carolina 27710, USA.
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Murday JS, Siegel RW, Stein J, Wright JF. Translational nanomedicine: status assessment and opportunities. NANOMEDICINE-NANOTECHNOLOGY BIOLOGY AND MEDICINE 2009; 5:251-73. [PMID: 19540359 DOI: 10.1016/j.nano.2009.06.001] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2009] [Accepted: 06/07/2009] [Indexed: 10/20/2022]
Abstract
UNLABELLED Nano-enabled technologies hold great promise for medicine and health. The rapid progress by the physical sciences/engineering communities in synthesizing nanostructures and characterizing their properties must be rapidly exploited in medicine and health toward reducing mortality rate, morbidity an illness imposes on a patient, disease prevalence, and general societal burden. A National Science Foundation-funded workshop, "Re-Engineering Basic and Clinical Research to Catalyze Translational Nanoscience," was held 16-19 March 2008 at the University of Southern California. Based on that workshop and literature review, this article briefly explores scientific, economic, and societal drivers for nanomedicine initiatives; examines the science, engineering, and medical research needs; succinctly reviews the US federal investment directly germane to medicine and health, with brief mention of the European Union (EU) effort; and presents recommendations to accelerate the translation of nano-enabled technologies from laboratory discovery into clinical practice. FROM THE CLINICAL EDITOR An excellent review paper based on the NSF funded workshop "Re-Engineering Basic and Clinical Research to Catalyze Translational Nanoscience" (16-19 March 2008) and extensive literature search, this paper briefly explores the current state and future perspectives of nanomedicine.
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Affiliation(s)
- James S Murday
- University of Southern California, Washington, DC 20004 USA.
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Abstract
There are more than forty million blind individuals in the world whose plight would be greatly ameliorated by creating a visual prosthesis. We begin by outlining the basic operational characteristics of the visual system, as this knowledge is essential for producing a prosthetic device based on electrical stimulation through arrays of implanted electrodes. We then list a series of tenets that we believe need to be followed in this effort. Central among these is our belief that the initial research in this area, which is in its infancy, should first be carried out on animals. We suggest that implantation of area V1 holds high promise as the area is of a large volume and can therefore accommodate extensive electrode arrays. We then proceed to consider coding operations that can effectively convert visual images viewed by a camera to stimulate electrode arrays to yield visual impressions that can provide shape, motion, and depth information. We advocate experimental work that mimics electrical stimulation effects non-invasively in sighted human subjects with a camera from which visual images are converted into displays on a monitor akin to those created by electrical stimulation.
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Affiliation(s)
- Peter H Schiller
- Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA.
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Tehovnik EJ, Slocum WM, Smirnakis SM, Tolias AS. Microstimulation of visual cortex to restore vision. PROGRESS IN BRAIN RESEARCH 2009; 175:347-75. [PMID: 19660667 DOI: 10.1016/s0079-6123(09)17524-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
This review argues that one reason why a functional visuo-cortical prosthetic device has not been developed to restore even minimal vision to blind individuals is because there is no animal model to guide the design and development of such a device. Over the past 8 years we have been conducting electrical microstimulation experiments on alert behaving monkeys with the aim of better understanding how electrical stimulation of the striate cortex (area V1) affects oculo- and skeleto-motor behaviors. Based on this work and upon review of the literature, we arrive at several conclusions: (1) As with the development of the cochlear implant, the development of a visuo-cortical prosthesis can be accelerated by using animals to test the perceptual effects of microstimulating V1 in intact and blind monkeys. (2) Although a saccade-based paradigm is very convenient for studying the effectiveness of delivering stimulation to V1 to elicit saccadic eye movements, it is less ideal for probing the volitional state of monkeys, as they perceive electrically induced phosphenes. (3) Electrical stimulation of V1 can delay visually guided saccades generated to a punctate target positioned in the receptive field of the stimulated neurons. We call the region of visual space affected by the stimulation a delay field. The study of delay fields has proven to be an efficient way to study the size and shape of phosphenes generated by stimulation of macaque V1. (4) An alternative approach to ascertain what monkeys see during electrical stimulation of V1 is to have them signal the detection of current with a lever press. Monkeys can readily detect currents of 1-2 microA delivered to V1. In order to evoke featured phosphenes currents of under 5 microA will be necessary. (5) Partially lesioning the retinae of monkeys is superior to completely lesioning the retinae when determining how blindness affects phosphene induction. We finish by proposing a future experimental paradigm designed to determine what monkeys see when stimulation is delivered to V1, by assessing how electrical fields generated through multiple electrodes interact for the production of phosphenes, and by depicting a V1 circuit that could mediate electrically induced phosphenes.
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Affiliation(s)
- Edward J Tehovnik
- Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
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Singh V, Roy A, Castro R, McClure K, Dai R, Agrawal R, Greenberg RJ, Weiland JD, Humayun MS, Lazzi G. On the thermal elevation of a 60-electrode epiretinal prosthesis for the blind. IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS 2008; 2:289-300. [PMID: 23853132 DOI: 10.1109/tbcas.2008.2003430] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
In this paper, the thermal elevation in the human body due to the operation of a dual-unit epiretinal prosthesis to restore partial vision to the blind affected by irreversible retinal degeneration is presented. An accurate computational model of a 60-electrode device dissipating 97 mW power, currently under clinical trials is developed and positioned in a 0.25 mm resolution, heterogeneous model of the human head to resemble actual conditions of operation of the prosthesis. A novel simple finite difference scheme combining the explicit and the alternating-direction implicit (ADI) method has been developed and validated with existing methods. Simulation speed improvement up to 11 times was obtained for the the head model considered in this work with very good accuracy. Using this method, solutions of the bioheat equation were obtained for different placements of the implant. Comparison with in-vivo experimental measurements showed good agreement.
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Bókkon I. Phosphene phenomenon: a new concept. Biosystems 2008; 92:168-74. [PMID: 18358594 DOI: 10.1016/j.biosystems.2008.02.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2007] [Revised: 02/10/2008] [Accepted: 02/12/2008] [Indexed: 02/01/2023]
Abstract
This paper proposes a new biopsychophysical concept of phosphene phenomenon. Namely, visual sensation of phosphenes is due to the intrinsic perception of ultraweak bioluminescent photon emission of cells in the visual system. In other words, phosphenes are bioluminescent biophotons in the visual system induced by various stimuli (mechanical, electrical, magnetic, ionizing radiation, etc.) as well as random bioluminescent biophotons firings of cells in the visual pathway. This biophoton emission can become conscious if induced or spontaneous biophoton emission of cells in the visual system exceeds a distinct threshold. Neuronal biophoton communication can occur by means of non-visual neuronal opsins and natural photosensitive biomolecules. Our interpretation is in direct connection with the functional roles of free radicals and excited biomolecules in living cells.
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Affiliation(s)
- István Bókkon
- PhD School in Pharmacology, Semmelweis University, Láng E. 68, H-1238 Budapest, Hungary.
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