The future of implantable neuroprosthetic devices: ethical considerations

1050-6934/09 $35.00 © 2009 by Begell House, Inc. 123

Journal of Long-Term Effects of Medical Implants, 19(2): 123–137 (2009)

The Future of Implantable Neuroprosthetic Devices: Ethical Considerations*†

Pratik Y. Chhatbar,1,2 & Subrata Saha*,1-4

1Graduate Program in Biomedical Engineering, 2Department of Physiology and Pharmacology, 3Department of Orthopedics and Rehabilitative Medicine, and 4Department of Neurosurgery,

SUNY Downstate Medical Center, Brooklyn, NY

*Address all correspondence to Subrata Saha, Department of Orthopaedic Surgery & Rehabilitation Medicine, SUNY Downstate Medical Center, 450 Clarkson Ave., Box 30, Brooklyn, NY 11203; Tel.: 718-613-8652; Fax: 718-270-3983; [email protected].

ABSTRACT: From well-established results with cochlear implants to the advent of implantable microelectrode arrays, implantable neuroprosthetic devices have gained increasing attention from health care professionals, scientists, engineers, and the general population. With recent depictions of neuroprostheses in the news media and in movies, confusion about their current state and concern for their future use has increased tremendously among members of the public. Many government agencies and non-government organizations are also concerned with the safety and efficacy of these devices. We discuss the present state of development of some of these implantable neuroprostheses, the possible future use of this technology, and the associated ethical issues that can be of concern, including manufacturing, animal experimentation, human trials, scope of use, and individual and societal concerns.

KEY WORDS: neuroprosthetics, neural prostheses, ethics, newer technologies, medical implants

I. INTRODUCTION

A neural prosthetic device or a neural prosthesis can be defined as a device implanted in the central or peripheral nervous system for the purpose of restoring or improving lost or altered neural function. A neural prosthesis can work as a stimulating device (e.g., cochlear implants for neural deafness, subthalamic implants for drug-refractory parkinsonism, and stimulation-based functional mapping of the cortex using subdural surface electrodes) or as a recording device (e.g., subdural surface electrodes to localize epileptogenic focus and multi-electrode implants to control cursor/robotic devices using motor cortex activity).

ABBREVIATIONS

BCI, brain-computer interface; ECoG, electrocorticography; EEG, electroencephalogram

†Presented in part at the Fifth International Conference on Ethical Issues in Biomedical Engineering, Brooklyn, NY, April 5, 2009, and at the 6th Annual World Congress of IBMISPS on Brain Mapping and Image Guided Therapy, Boston, MA, August 28, 2009.

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FIGURE 1. Number of publications based on PubMed database for different keywords related to neural prostheses up to September 2009.

Currently, multitudes of such neural prostheses are available commercially, and many of them are being investigated for modifying existing technology

or as de-novo technologies. We have observed an increasing interest in the field, as objectively evidenced by publication trends in scientific journals for past few years (Fig. 1).

The cochlear implant, developed in the 1950s, is perhaps the first commercially used neural prosthesis, and has helped thousands of deaf children and adults around the globe by partially restoring their hearing.1 The development from a single channel initially to today’s 32-channel cochlear implant has increased functionality, with users able to actually understand a simple, day-to-day conversation just by listening.2

The use of a subthalamic implant as a therapy for drug-refractory parkinsonism is based on the same principle of micro-stimulation as the cochlear implant.3 While the latter stimulates the cochlea, a part of the peripheral nervous system, a subthalamic implant stimulates the deep-brain structures. This in turn stimulates/inhibits selected pathways in the brain network responsible for impairment of motor function, allowing easy initiation of movements and minimizing resting tremors.

A widely used surgical technique for epilepsy is

FIGURE 2. Schematic diagram of a cochlear implant (reproduced from National Institute of Health, US Department of Health and Human Services).

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125NEUROPROSTHETIC DEVICES: ETHICAL CONSIDERATIONS

the placement of temporary neural prosthetics, which are comprised of a subdural electrode strip, grid electrodes, or depth electrodes reaching deep into the hippocampal region of the temporal lobe.4 Patients with recurrent seizures and poor medical response or compliance can be candidates for resection of the epileptogenic focus, which is commonly located in or around the temporal lobe. Before the actual resection, these patients undergo implantation surgery of electrodes and are then followed for days to weeks without anti-epileptic medications in order to locate the exact site of seizure origin.

The second use of these implanted electrodes is to determine possible functional impairment caused by resection of underlying or surrounding brain region.5 The electrodes are stimulated to offer non-functionality to the surrounding brain region while patients perform routine day-to-day conversations or related tasks. This helps to delineate the margin of surgical resection and predicts any possible post-resection disability. Finally, in the second and final surgery, these electrodes and the part of the brain with epileptogenic focus are resected.

Considerable research has been conducted in the past decade on the active development of permanent cortical implants.7-11 Some sensorimotor implants are undergoing active human trials to restore the function of denervated limbs or replacement of resected limbs with robotic limbs controlled by brain signals.12-15 This neural prosthetic device can be a pure recording device, the signals from which might be used to move the limb or a robot; it can also be a combination of recording and stimulating units that send the state information of the limb or robot back to the brain, thus closing the loop and enabling more access and freedom to the user. This differs from visual or auditory cortical implants, in which the implanted microelectrodes are used purely to stimulate the neural substance based on the visual/auditory signals that the external sensors receive.16-17 In this technique, the microstimulation site may be located in the central nervous system, for example, in the cerebral cortex or a deep structure such as the lateral or medial geniculate nucleus, instead of in a peripheral nervous system organ such as the cochlea (in the case of cochlear implants) or the retina (in the case of retinal implants).18-21

Recently, there has been increased interest within the clinical and research community in peripheral nervous system neural prostheses. In this technique, a microelectrode array in the same or slightly modified configuration as used for the brain is implanted in a peripheral nerve22 such as the sciatic nerve23 (for a lower limb) or a member of the brachial plexus (for an upper limb). Through this implant, the nerve fascicles can be monitored or stimulated to receive the sensory information the nerve is carrying or feed motor commands that the muscles can use in order to move the limb, respectively.

FIGURE 3. A parkinsonian patient undergoing a subthalamic implant procedure with a framed ste-reotaxy. Newer methods of such implantation pro-cedures do not involve such frames, and thus are called frameless stereotaxy. Here the precise loca-tion of an electrode tip is determined by preopera-tive or intraoperative MRI. An even newer method is intraoperative three-dimensional USG. (Image is from Wikimedia Commons.)

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A slight extension of peripheral nervous system neural prostheses, which is not technically a neural prosthesis in the pure sense, but resembles it enough to be mentioned here, is a myoelectric prosthesis.24 Here diversion and implantation of the nerves feeding the resected limb is performed on the pectoral muscles. The patient can use electromyelogram signals to control the multiple degree-of-freedom robotic arm. The sensory counterpart of this would be a tactile stimulator on the chest, neck, or cheek, which is used on an amputee with or without the diversion and implantation of the nerves feeding the resected limbs on the skin as the tactile stimulation site.25 In a nutshell, the touch pattern generated by the tactile stimulator is received on these diverted nerves, and thus the patient feels sensations that are similar to the sensations on the amputed limb. This can be compared with the peripheral nervous system type of prosthesis, but the quality and richness heavily depend on the innervations of the diverted nerve and the spatiotemporal resolution of the tactile stimulator that is partly controlled by its physical properties. Many such diversions and extensions of the peripheral nervous or myoelectric prostheses are being investigated, with varying degrees of success.

II. CURRENT AND POTENTIAL USES OF NEURAL PROSTHESES

As of now, very few neural prostheses are being used successfully on a commercial basis. Some examples are cochlear implants in patients with profound sensorineural deafness and subthalamic implants in patients with drug-refractory parkinsonism. Cochlear implants27-28 have contributed significantly to improving the user’s quality of life, and have a long track record regarding their safety and efficacy; however, the long-term effects and failure rates of newer techniques such as subthalamic implants29-31 are still not well established. There is also insufficient evidence in humans on the neural control of external devices13 such as a computer cursor, and simple technological extensions such as moving a limited degree-of-freedom hand and wheelchairs.

Implantable visual prosthetic devices for the future may have prostheses implanted in the retina32

or subretinal region,33 the optic nerve,34-35 lateral

geniculate nucleus,36-37 or visual cortex.38 This would help blind people to have at least a “pixilated” view of the outside world, just as cochlear implants provide tones of limited frequency values. However, this application, once sophisticated technologically, might also serve as an accessory visual stimulation pattern in which a person can actually get additional relevant information based on the location and the scene one is looking at.

Attempts have also been made to create implants for hearing-impaired patients in whom the cochlea is non-functional or inert for electrical stimulation. Future auditory prostheses may include a cochlear nerve implant,22 auditory brainstem implant,39

inferior colliculus implant, medial geniculate nucleus implant, or auditory cortex implant.40

The idea behind the development of such prostheses is to restore or improve the function of a disabled person, just like having glasses for eye refraction improvement (an example of disability improvement) or having cataract surgery (an example of restoration of a function). However, going a step further, the integration of visual, auditory, somatosensory, and motor neural prostheses can lead to new applications that may change drastically the way we think and live. Just contemplating the consequences of such futuristic developments might give a bewildering feeling given the current state of technology use. For example, visual prostheses might obviate the need for a television set. With the help of sensorimotor prostheses, we may not need a keyboard or a mouse to operate computers. Given the dynamic nature of the sensorimotor cortex, it can be trained to operate buttons ranging from a simple light switch to complicated cell phones without buttons or a touch screen. Telecommunication devices such as cell phones may possibly communicate wirelessly with auditory implants to send the voice and may be able to get speech signals from an implant in Broca’s area to send it to the party on the other end. Because of the generic nature of the neural implant and transfer protocols, it might be possible to use a somatosensory implant to enjoy remotely the texture and feel of the cloth that one is about to buy in a store. Hippocampal implants with micro-needles may help patients to selectively forget traumatic experiences or events using substances such as



protein kinase M-zeta (PKMζ),41-42 decreasing the chances of the subject being affected by psychiatric problems such as acute or post-traumatic stress disorder.

Programmed peripheral muscular stimulation might mean smaller, shorter workout sessions with manifold and speedy buildup of muscle mass without actually having neural fatigue caused by presynaptic neurotransmitter exhaustion. This technique might also be able to give an additional boost to the muscles of a soldier to reach toward or away from the enemy at a little faster speed or farther distance. Motor cortical activity might control multiple prosthetic arms at the same time, effectively using the very neural signals to control a variety of instruments. This can range from big cranes and bulldozers for routine construction chores to precision work such as robotic microsurgery,43-44 in which activity from a larger brain area can be used for a lesser degree-of-freedom task. The use of multiple different instruments, such as handling multiple machine guns, rocket launchers, and missiles while controlling a fighter airplane or a tank while simultaneously communicating with other soldiers might also be possible. In short, peripheral muscle stimulation can take over dexterous hand/foot maneuvers with increased precision. This all might sound like a fairy tale now, but we strongly believe that the possibilities are infinite, and that realization of it is a question of when rather than if. After the discussion on the current state of neural prostheses below, we hope to make the above-stated claims sound somewhat feasible, not a trivial extension of current technology.

III. CURRENT RESEARCH ON DEVELOP-MENT OF NEURAL PROSTHETIC DEVICES

Our senses are divided into two broad categories: general senses and special senses. General senses include touch, pressure, pain, temperature, vibration, etc., broadly covering the sensations that we get through our skin and underlying tissues, which have various sensory nerve endings. Vision, hearing, taste, and smell are classified as special senses. As of today, the majority of the work on neural prostheses is related to vision and hearing (special senses) and touch (a general sense). Recently proprioception has

started getting a lot of attention because of its role in artificial limbs, but relatively little work has been conducted in the field of taste, smell, temperature, or pain in terms of restoration of these modalities using prosthetic devices. This is possibly because of their limited role in terms of rehabilitation (taste, smell) and easy detection by simple sensors (temperature).

For decades, there has been a tremendous amount of interest in neural prostheses, as evidenced by the many movies, serials, novels, etc., related to some sort of brain-machine interface. However, even considering the progress we have made in this field in past couple of decades, it is no exaggeration to state that the real status of the technology is still in its infancy. There are many hurdles on the way to perfecting this technology, and many breakthroughs to achieve before we shall actually start enjoying its benefits. It does not seem impossible to achieve some of the benefits considering the rapid progress the science has made; however, it is definitely a much more difficult task than most might realize.

The possibility of having full-fledged visual or auditory prosthetic devices is still a long way off, considering its limited trials in humans18,45

and the difficulty of inferring the perceptions and thus behavioral studies after implantation in animal models.46-47 On the other hand, in animal models10-11,14,48-49 and in human experimentation,13,50 the use of chronic multi-electrode array implantation in sensorimotor cortices has been demonstrated. In this procedure, virtual or prosthetic limb movement is accomplished by switching between the brain control mode and the hand control mode. This makes the implementation of sensorimotor prostheses a more likely possibility in near future.

The use of noninvasive electroencephalogram (EEG) recordings to control a remote robot has been attempted,51 and similar signals are used to control wheelchairs.52 Stimulating the spinal cord, peripheral nerves, or even muscle directly to generate limb movements has also been investigated, sometimes with successful patient application.53

Electrocorticography (ECoG) has recently been tried to control the cursor with the leads over the sensory and/or motor cortex.54 ECoG is considered superior to EEG because of the higher signal-to-noise ratio attributed to subdural lead placement

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or needle electrodes. However, it is a less likely choice because of its invasive nature. Evidence of possible brain-computer interfacing (BCI) using thalamic/subthalamic recordings in some awake human subjects under acute setup14 has shown some exciting possibilities. Chronic cortical multi-electrode implant13 also has a comparable success rate, but definitely needs further investigation.

The ultimate goal of these neural prostheses

would be to successfully implement real-time BCI. The use of noninvasive EEG recordings on humans has been demonstrated by various groups,51,55 and some patients have been able to control the orthosis.56 The use of EEG signals has been extended to such things as video games57 but also for some real-life problem solutions such as switching for paralytics.58 The success of EEG technology can be attributed to its noninvasive nature, which allows

FIGURE 3. ECoG array in situ. (A) Exposed brain after craniotomy. (B) 8 × 8 electrode grid on the surface of the brain. (C) Lateral x-ray image showing the electrode grid and several strips. (D) Average brain tem-plate and electrode locations co-registered to the x-ray image. (Reproduced with permission from Schalk et al., 2008.6)



the experimenter access to a higher number of subjects and volunteers and thus more opportunity to optimize the signal interpreting algorithm. Conversely, invasive implantable devices have a high signal-to-noise ratio and require surgery and strict adherence to protocol, significantly limiting the number of subjects and experiments. Also, behavioral training for non-human primates48 takes at least a few months to make them reasonably proficient in the particular task.

IV. MANUFACTURING AND DIFFERENT IM-PLICATIONS

The neuroprostheses currently in use are made from a wide variety of components that directly or distally record from or stimulate the neural substance. These include everything from familiar EEG metal leads57

to recently Food & Drug Administration (FDA)-approved temporary devices such as Cereport,13

which are made of platinum with or without an iridium oxide coating. A vast variety of electrodes are currently in use in humans to find epileptic focus4 or to treat drug-refractory parikinsonism.3

Here we briefly discuss only the aspects and parts of the manufacturing processes that directly deal with the health of the end-user and the personnel involved in such processes.

Like any other manufacturing process, neuroprostheses have to undergo different stages of development to reach the final state, and this involves molding, hybridization, functionalization, coating, etc. The most important concerns are that the materials are proven to be bio-friendly and non-hazardous, and that the manufacturing process as a whole is ecologically sound. Both of these issues can be exemplified by the new, potentially promising technology of carbon nanotubes.

Carbon nanotubes as an integral material of implantable microelectrodes have been used for recording purposes in neuronal cultures in vitro,60-61 in small animals,61 and even in non-human primates.61

There have also been reports of stimulation of the neural substrate through carbon nanotubes after appropriate functionalization.62 These results are exciting and appear to be promising, but the overall effect of carbon nanotubes on health is still unknown. Some recent reports have documented

their effects on different systems of the body,63-

69 but this information might not be adequate to actually advocate the use of carbon nanotubes for different applications, including neuroprostheses, for the population at large. Similarly, reports on the manufacturing process of carbon nanotubes and its effect on the health of the personnel involved70-73

should be considered with the utmost scrutiny because the only way to deal with potential hazards of new unknown technology is to prevent them.

V. ANIMAL TRIALS

FIGURE 5. Drawing of the second-generation neu-roprosthetic system. The internal components in-clude the IST-12, 12 stimulating electrodes (not all shown), and two recording electrodes. The exter-nal components include the control unit and the transmit/receive coil. This system provides grasp/release, forearm pronation, and elbow extension with myoelectric control for improved function in the tetraplegic spinal cord-injured individual. MES, myoelectric signal. (Reproduced with permission from Kilgore et al., 2008.26)

Just like most new medical or surgical techniques, thorough animal experimentation should be conducted before the new technology of neuroprosthetics is used on humans. One can always question and object to the need for animal trials, but at the same time one has to consider the benefits of such trials in terms of higher success rates for human use. Therefore, the non-hazardous nature of such new technology needs to be demonstrated by

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controlled experiments on other species.Animal trials have to be designed humanely

and in such a way as to minimize the number of compromised animals by maximizing the results obtained from a single animal. Apart from being frugal in the use and duration of use of animals, we should consider it more appropriate to use animals of lower taxonomical classification whenever possible.

With technological advancements, especially in the field of computers, modeling of a biological system in a more realistic way has sometimes been possible. If by utilizing mathematical modeling we can estimate the results that we can get from animal experimentation, this can drastically decrease the need for animal trials. Such modeling may allow the investigator to test only a few animals to demonstrate the proof of the principle that

FIGURE 6. Left, Carbon nanotube (CNT) island on a single microelectrode (×9500). Note the porous na-ture of the CNT island. Right, Four such islands can be seen with a retina laid on such a microelectrode array in vitro (×32). An arrow points to a retinal ganglion cell and asterisks to blood vessels. (Reproduced with permission from Shoval et al., 2009.59)

FIGURE 7. Schematic diagrams of the currently used experimental setup of closed-loop brain-machine interface, controlling robotic arm (left, reproduced with permission from Carmena et al., 200310) or the paralyzed limb (right, reproduced with permission from Pohlmeyer et al., 200974).

https://www.researchgate.net/publication/24416166_Carbon_Nanotube_Electrodes_for_Effective_Interfacing_with_Retinal_Tissue?el=1_x_8&enrichId=rgreq-97c28a00-b93a-406a-8c16-c580c6860fd6&enrichSource=Y292ZXJQYWdlOzQ1NDA1MDk2O0FTOjk5OTIyMDgyNzk1NTQwQDE0MDA4MzQ2ODk3NTg=



FIGURE 8. An experimental implant device capable of carrying connectors from multiple microelectrode arrays, thus giving access to hundreds of implanted microelectrodes while limiting the exposed scalp skin margin and thus decreasing the chances of infections and other complications. (A) Monkey enjoying an apple; (B) view from the back while seated; (C) assembly with head stages plugged in. (Reproduced from Chhatbar et al, 201079)

FIGURE 9. Braingate (left) and recent Braingate2 (right), two of the most famous clinical trials of senso-rimotor neuroprostheses. (Reproduced from http://www.braingate.org/ and with permission from Song et al., 2009.76)

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has been developed through extensive simulation and calculations. Similarly, in vitro experiments should be encouraged over in vivo trials whenever possible.

VI. CLINICAL TRIALS

Once animal trials are completed, the next step for most technology before being marketed to the general population is to undergo clinical trials, which is testing of the technology on a limited number of people to prove its non-hazardous nature and efficacy. Fortunately for the field of neural prosthetics, cochlear implants have been used routinely for decades on deaf patients,1 and long-term reports on subthalamic implants are also being reported.30 Trials of sensorimotor prostheses for tetraplegic humans have been approved by the FDA,13,75 although with some limitations on their duration. This has generated high hopes for the use of these and other neuroprosthetic devices. It might not be an exaggeration to state that the days of routine neural prosthetic implants in disabled, or even healthy, people may not be far away.

Even in such an advanced state of development, one should point out that neuroprostheses may have their own complications. Gliosis and infection with invasive neural interfaces and relatively lower precision with noninvasive methods of neural interfaces need careful evaluation before considering this technology as self-sufficient, independent, and accountable for short- and long-term use. Institutional Review Boards, the US Health & Human Services Department (via the Health Insurance Portability and Accountability Act), and other agencies dealing directly or indirectly with clinical trials have to be cautious in reviewing proposals in light of the rapidly changing and growing field of neural prostheses. New products and their extensions and/or modifications are being introduced rapidly, and sometimes may not even have FDA approval for clinical trials before being marketed to physicians, and thus their hospitals and patients.

Another major consideration in clinical trials is the need for informed consent. One problem here is that informed consent cannot be fully “informed” in a true sense because no one can predict the outcome

of this new treatment. Therefore, investigators should include in their proposals as many scenarios as possible for favorable and unfavorable outcomes and potential remedies to deal with them to minimize confusion and apprehension due to unexpected events during clinical trials.

Compensation for clinical trial participants is another sensitive issue that needs to be addressed carefully. With growing awareness about newer technologies and faster means of communication, today’s patient is more informed than ever. Considering the potential benefits of neural prostheses, there is a good chance that investigators will have access to informed volunteers who are interested in the favorable outcome of this new technology and would therefore consider it as compensation itself. However, the investigator and the design of the experiment have to make it clear that this is merely a clinical trial and not a treatment option. In fact, clinical trials should not be highlighted as a treatment option, which can be considered unethical and misleading. This will avoid creating unrealistic hopes for potential recipients of the new technology who may participate in clinical trials with uncertain outcomes.

VII. HUMANE USE OF TOMORROW’S NEU-RAL PROSTHESES

Today’s widely used neural prostheses are primarily used to correct disabilities. Cochlear implants give a crude sense of hearing, while subthalamic implants provide tremor-free movements of relatively rapid onset compared with a debilitated parkinsonian state. Newer developments in the field of neuroprosthetics might make it possible for anyone not only to regain vision, muscle power, or mobility, but also to enjoy the link between electronics and the brain. Examples include neural control of telecommunications, and in this regard the possibilities are infinite. Unfortunately, it may be very difficult to keep track of the full functionality provided by the so-called “brain-machine interface” compared with simple electronic circuits that have the functionality to track and log all activities. In this way, the technology might be misused if it falls into the wrong hands.



VIII. RESTORATION VS. SUPPLEMENTA-TION

Another sensitive issue with the use of the neural prostheses is the need to limit their use to a certain extent. With the development of new technologies, the functionality in use today might grow beyond anyone’s expectations. To illustrate, cochlear implants, when launched decades ago, had a single channel that gave the deaf patient an ability to have a binary sense of sound, which included only a certain frequency range above a certain amplitude. The number of channels has increased today and ranges from 16 to 32, which now enables the patient with profound hearing loss to enjoy music and actively participate in regular conversations. Similar assumptions and projections can be safely made for visual and other neural prostheses a few decades down the line. For example, after a few decades, a sight-impaired person may be able to see with a resolution comparable to those with healthy eyes, or normal vision may be supplemented so as to make the experience as vibrant as that observed in birds. The olfaction sense might be supplemented using the same technology, thus making biosensors capable of sending information directly into the brain in real time. Sensorimotor neural prostheses can control an exoskeletal robotic system that may be stronger and more robust than the human musculoskeletal system.

Beyond our five modalities of senses, neural prostheses can be used to give us a totally novel modality of a sense. For example, ultrasound or sonar system can be designed to send signals to the brain. Put simplistically, frequency coding of a single microstimulation channel in the brain can be a function of the distance of an object as detected by an ultrasound. In this way, a person can have a sense of the distance of an object, not through stereotactic vision but through a new modality similar to that which bats use to map out their surroundings and locate prey. This suggests that the neuroprosthetics can be used not only for improvement or restoration of a disability, but also for supplementation or super-ability achievement. A person with supplementation may become superior to others because of the special senses or powers that the novel use of neural

prostheses can provide. With this additional ability comes additional freedom for the person to use it in a productive or destructive way. A vivid, fictional example of this is “Dr. Octopus” as portrayed in the movie based on the famous comic book character Spiderman.77 This is a potential issue of tomorrow that needs attention today considering the pace at which this technology is progressing.

IX. VARIOUS IMPLICATIONS OF NEURAL PROSTHESES USAGE AND CONCLUSION

We already have touched upon many current and potential uses of neural prostheses. The only thing we can say with certainty about the future of this field is that it is growing faster than ever. Our five bodily senses, vision, hearing, smell, taste, and touch, can all have external interfaces that can restore or supplement their function. Advances in electronics and telecommunications, combined with the dynamicity and plasticity of our nervous system, mean that novel uses of neural prostheses can easily exceed the functions of the highly specialized biological sensors such as the organ of Corti of the cochlea or the rods and cones of the retina.

A telecommunication chip with adequate neural connections can obviate the need not only for a cell phone but also for the hearing and speaking mechanism itself. The amount of information transferred in this way might be much less than traditional talking, which can save a large amount of dedicated neural substrate required purely for the act of talking, and would also be lighter on both energy consumption and electronic data transfers. The possibilities are infinite. The question doesn’t seem to be one of if, but rather when, as to the progression from the current nanoscale level of technological progress in neural prostheses to the gigascale level of proficient implementation.78

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The future of implantable neuroprosthetic devices: ethical considerations

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