Brain Behav. Evol. 14: 7-9 (1977)
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Neural Prostheses K. F rank and F. T. H ambrecht National Institute of NeuroLogical and Communicative Disorders and Stroke, National Institutes of Health, Bethesda, Md.
Key Words. Neural prosthesis • Auditory prosthesis ■Visual prosthesis ■Electrophrenic respiration • Electrode • Stimulation
The direct control of certain aspects of the human nervous system by externally applied signals or the utilization of signals from the nervous system to directly control external devices are both examples of neural control. Neural prostheses are a form of neural control in which an at tempt is made to restore lost neurological function. The best known ex ample is the artificial cardiac pacemaker which supplies missing signals to trigger cardiac muscle contraction. This is a relatively simple device com pared to other neuroprostheses presently being investigated. Another neuroprosthesis which has reached the clinical evaluation stage is electrophrenic respiration. If the control signals to the phrenic nerves which innvervate the diaphragm are absent due to a spinal cord in terruption or a defect in the respiratory centers of the brain, normal breathing is not possible. Until recently, persons with these types of de fects required mechanical respirators. If the diaphragm and lungs are intact and the phrenic nerves are not injured, it is possible to electrically stimulate the phrenic nerves. G len n et al. [2] have developed a successful treatment for these patients utilizing this technique. As attempts are made to apply neural prostheses more centrally in the
Downloaded by: Lund University Libraries 130.235.66.10 - 1/1/2019 10:01:57 PM
Abstract. The objectives of several neural prostheses which are currently being investigated are discussed along with some of the principal research questions. Fu ture neural prostheses may extend mans’ capabilities beyond that which is consid ered normal function.
F rank /H ambrecht
nervous system, the complexity of the problems and the devices increases. The studies reported in this symposium were originally inspired by the work of B rindley and L ewin [1] on the development of a visual prosthe sis for the blind. Essentially this prosthesis would utilize electrical stimu lation of the visual cortex by an array of electrodes on the pial-arachnoid surface. Such stimulation results in sensations of light, called phosphenes, whose position in the subject’s visual field is determined by the location of stimulation on the cortex. The prosthesis would contain a television camera or other image-sensing device and appropriate electronic process ing circuitry to control the spatiotemporal activation of the electrodes. It is hoped that phosphene patterns can be generated which are simple ap proximations of images sensed by the camera. Such prostheses would be used by the blind for a reading and mobility aid. The work reported by B rindley was encouraging, but many basic fea sibility questions remain to be answered. It was not known whether the visual cortex could survive continuous, long-term electrical stimulation. Would the electrodes proposed resist corrosion and would there be any toxic electrochemical species produced at the electrode tissue interface? Could electrodes be designed so that they would not produce any solution species? What are the mechanisms of neural excitation by electrical stim ulation and how can the rate of information transfer into the visual sys tem be increased? In 1970, the National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) initiated a contract program to attempt to answer these and related feasibility questions. The papers in this sym posium represent some of the results from this program. It has been readily apparent that these studies are applicable to many other neural prosthetic devices. For example, the electrochemical and corrosion analyses are fundamental to all prostheses that use metallic-sti mulating electrodes. Such studies have also led to the development of new types of electrodes such as the capacitor stimulating electrode [3], A related, sophisticated device which is being investigated, is an audi tory prosthesis for the deaf. This is based on the sensations of sound pro duced by electrical stimulation of the auditory nerve and would be useful only in deaf patients who have some remaining function in the nerve. The most popular approach presently being studied, is to place an array of electrodes into the scala tympani of the cochlea in a manner which per mits spatially selective stimulation of the nerve as it fans out and termi nates along the basilar membrane. Methods are being developed to drive
Downloaded by: Lund University Libraries 130.235.66.10 - 1/1/2019 10:01:57 PM
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Neural Prostheses
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the electrodes with electrical signals which are encoded by auditory infor mation. It is hoped that a deaf patient fitted with such a device will be able to understand normal speech. Unfortunately, nerve regeneration and repair is limited in the nervous system of mammals, particularly in the central nervous system. Hopeful ly, it may be possible in the future to overcome the barrier which blocks regeneration. Until then, artificial means such as those discussed must be developed to help restore function in patients with neural deficits. How ever, one need not necessarily limit prosthetic development to replacing lost function. It is conceivable that methods of information transfer can be developed which are much faster and more efficient than those which involve our sensory organs or our neuromuscular effectors (muscles). For example, ultimately one brain may be able to communicate directly with another through the transformations provided by a computer. Similarly, it should be possible to control devices directly by signals from the central nervous system, permitting the elimination of the slow and physically lim ited muscular control link [4].
References
Dr. K. F rank, National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health, Betliesda, MD 20014 (USA)
Downloaded by: Lund University Libraries 130.235.66.10 - 1/1/2019 10:01:57 PM
1 Brindley, G. S. and L ewin , W. S.: The sensations produced by electrical stimu lation of the visual cortex. J. Physiol., Lond. 196: 479-493 (1968). 2 G lenn, W. W. L. H olcomb, W. G.; H ogan, J.; M atano, I.; G ee , J. B. L.; M otoyama, E. K.; K im , C. S.; P oirier , R. S., and F orbes , G.: Diaphragm pacing by radio frequency transmission in the treatment of chronic ventilatory insufficien cy. J. thorac. cardiovasc. Surg. 66: 505-520 (1973). 3 G uyton, D. L. and H ambrecht, F. T.: Theory and design of capacitor elec trodes from chronic stimulation. Med. Biol. Engng 12: 613-620 (1974). 4 H ambrecht, F. T. and F rank, K.: The future possibilities for neural control; in M arton Advances in Electronics and Electron Physics, vol.38, pp. 55-81 (Aca demic Press, New York 1975).
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V
Neural Prostheses K. F rank and F. T. H ambrecht National Institute of NeuroLogical and Communicative Disorders and Stroke, National Institutes of Health, Bethesda, Md.
Key Words. Neural prosthesis • Auditory prosthesis ■Visual prosthesis ■Electrophrenic respiration • Electrode • Stimulation
The direct control of certain aspects of the human nervous system by externally applied signals or the utilization of signals from the nervous system to directly control external devices are both examples of neural control. Neural prostheses are a form of neural control in which an at tempt is made to restore lost neurological function. The best known ex ample is the artificial cardiac pacemaker which supplies missing signals to trigger cardiac muscle contraction. This is a relatively simple device com pared to other neuroprostheses presently being investigated. Another neuroprosthesis which has reached the clinical evaluation stage is electrophrenic respiration. If the control signals to the phrenic nerves which innvervate the diaphragm are absent due to a spinal cord in terruption or a defect in the respiratory centers of the brain, normal breathing is not possible. Until recently, persons with these types of de fects required mechanical respirators. If the diaphragm and lungs are intact and the phrenic nerves are not injured, it is possible to electrically stimulate the phrenic nerves. G len n et al. [2] have developed a successful treatment for these patients utilizing this technique. As attempts are made to apply neural prostheses more centrally in the
Downloaded by: Lund University Libraries 130.235.66.10 - 1/1/2019 10:01:57 PM
Abstract. The objectives of several neural prostheses which are currently being investigated are discussed along with some of the principal research questions. Fu ture neural prostheses may extend mans’ capabilities beyond that which is consid ered normal function.
F rank /H ambrecht
nervous system, the complexity of the problems and the devices increases. The studies reported in this symposium were originally inspired by the work of B rindley and L ewin [1] on the development of a visual prosthe sis for the blind. Essentially this prosthesis would utilize electrical stimu lation of the visual cortex by an array of electrodes on the pial-arachnoid surface. Such stimulation results in sensations of light, called phosphenes, whose position in the subject’s visual field is determined by the location of stimulation on the cortex. The prosthesis would contain a television camera or other image-sensing device and appropriate electronic process ing circuitry to control the spatiotemporal activation of the electrodes. It is hoped that phosphene patterns can be generated which are simple ap proximations of images sensed by the camera. Such prostheses would be used by the blind for a reading and mobility aid. The work reported by B rindley was encouraging, but many basic fea sibility questions remain to be answered. It was not known whether the visual cortex could survive continuous, long-term electrical stimulation. Would the electrodes proposed resist corrosion and would there be any toxic electrochemical species produced at the electrode tissue interface? Could electrodes be designed so that they would not produce any solution species? What are the mechanisms of neural excitation by electrical stim ulation and how can the rate of information transfer into the visual sys tem be increased? In 1970, the National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) initiated a contract program to attempt to answer these and related feasibility questions. The papers in this sym posium represent some of the results from this program. It has been readily apparent that these studies are applicable to many other neural prosthetic devices. For example, the electrochemical and corrosion analyses are fundamental to all prostheses that use metallic-sti mulating electrodes. Such studies have also led to the development of new types of electrodes such as the capacitor stimulating electrode [3], A related, sophisticated device which is being investigated, is an audi tory prosthesis for the deaf. This is based on the sensations of sound pro duced by electrical stimulation of the auditory nerve and would be useful only in deaf patients who have some remaining function in the nerve. The most popular approach presently being studied, is to place an array of electrodes into the scala tympani of the cochlea in a manner which per mits spatially selective stimulation of the nerve as it fans out and termi nates along the basilar membrane. Methods are being developed to drive
Downloaded by: Lund University Libraries 130.235.66.10 - 1/1/2019 10:01:57 PM
8
Neural Prostheses
9
the electrodes with electrical signals which are encoded by auditory infor mation. It is hoped that a deaf patient fitted with such a device will be able to understand normal speech. Unfortunately, nerve regeneration and repair is limited in the nervous system of mammals, particularly in the central nervous system. Hopeful ly, it may be possible in the future to overcome the barrier which blocks regeneration. Until then, artificial means such as those discussed must be developed to help restore function in patients with neural deficits. How ever, one need not necessarily limit prosthetic development to replacing lost function. It is conceivable that methods of information transfer can be developed which are much faster and more efficient than those which involve our sensory organs or our neuromuscular effectors (muscles). For example, ultimately one brain may be able to communicate directly with another through the transformations provided by a computer. Similarly, it should be possible to control devices directly by signals from the central nervous system, permitting the elimination of the slow and physically lim ited muscular control link [4].
References
Dr. K. F rank, National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health, Betliesda, MD 20014 (USA)
Downloaded by: Lund University Libraries 130.235.66.10 - 1/1/2019 10:01:57 PM
1 Brindley, G. S. and L ewin , W. S.: The sensations produced by electrical stimu lation of the visual cortex. J. Physiol., Lond. 196: 479-493 (1968). 2 G lenn, W. W. L. H olcomb, W. G.; H ogan, J.; M atano, I.; G ee , J. B. L.; M otoyama, E. K.; K im , C. S.; P oirier , R. S., and F orbes , G.: Diaphragm pacing by radio frequency transmission in the treatment of chronic ventilatory insufficien cy. J. thorac. cardiovasc. Surg. 66: 505-520 (1973). 3 G uyton, D. L. and H ambrecht, F. T.: Theory and design of capacitor elec trodes from chronic stimulation. Med. Biol. Engng 12: 613-620 (1974). 4 H ambrecht, F. T. and F rank, K.: The future possibilities for neural control; in M arton Advances in Electronics and Electron Physics, vol.38, pp. 55-81 (Aca demic Press, New York 1975).
