Among the most intriguing beings in the virtual history are those that combine the living with the nonliving, such as the cyborgs Deirdre and RoboCop. These particular examples consist of a machinelike body of superior physical capability that is controlled by an implanted human brain. A hybrid being might also begin as an ordinary human, who is significantly modified with artificial parts or implants. (This is how the Tin Woodman became what he is in The Wizard of Oz: he started as a human, but as he accidentally chopped bits off himself and had them replaced by a tinsmith, he eventually became wholly metallic.) In either case, there is poignancy in the merging of human softness and frailty with the hard precision and power of a machine, and in the extreme, in the image of a mind and spirit isolated from the run of humanity within a dead shell.

It is easy to imagine such a hybrid as a spiritual amphibian, infinitely more displaced and alienated than, say, a person caught between two cultures and not fully belonging to either. At a deeper level, human–machine amphibians force us into a close examination of what living and nonliving really mean. In these beings, the boundary between the two states blurs, providing a third mode of existence that lies somewhere between unfeeling machine and feeling human.

However, in the real rather than the virtual world, there are as yet no human brains operating in artificial bodies. And although bionic people have been around for a long time, until recently their artificial parts have been primarily mechanical, not neural, and represent relatively small bodily changes. Replacements for missing limbs and cosmetic additions such as breast implants are immensely significant to the implantee, but they do not turn people into cyborgs—nor is anyone yet proposing to transplant a living brain into a metal body. Still, the latest chapter in the real history of artificial beings is a step toward this fusion; it is the formation of direct connections between living organic systems and nonliving ones at the neural and brain levels.

The key idea behind this synthesis draws on the electrical nature of the signals in the nerve network and the brain and envisages connecting neural systems to electronic ones. Outcomes already beginning to be realized include an interface that allows a paralyzed person to manipulate a computer purely by mental control, without physical effort; hybrid neural-electronic chips, in which a living neuron and an electronic circuit mounted on the same piece of silicon communicate with each other; and the use of animal brains to control mobile bodies and robotic arms, as a step toward providing mentally controlled devices to the paralyzed.

These developments fall under new areas in neural research and clinical practice called neurorobotics or neuroprosthesis, but artificial additions to human bodies have a long history that—like the development of artificial beings themselves—reflects successive waves of technology. Prostheses that use digital electronics owe their invention, in turn, to the development of implant surgery and to the scientific introduction of electricity into the body. But first came simpler physical prostheses without electronic components, made to meet the needs of those born handicapped, injured through accident, or wounded in war. Such prostheses fell into two categories: functional, to replace lost physical capability, and cosmetic, to rehabilitate damaged appearance.

Both functional and cosmetic rehabilitation were recognized in the early virtual history of bionic beings. What is said to be the first prosthetic described in writing appeared two to three millennia BCE in the Indian Rig-Veda poem, in which Queen Vishpla, having lost a leg in battle, replaces it with an iron one and returns to the fight. Other prosthetic devices have appeared in Greek mythology. Although Hephaestus, that limping Greek god of technology, did not use an artificial limb, he relied on a crutch and on the help of the golden assistants he had constructed. In an especially gruesome Greek tale, Tantalus, son of Zeus, killed and cooked his son Pelops and served him to the gods to see if they could distinguish between human and animal flesh. After Demeter, goddess of agriculture, ate Pelops’s shoulder, she atoned by restoring him to life complete with a new ivory shoulder. Prosthetics entered Greek culture in a different way in the fifth century BCE, when Aristophanes’ play The Birds included a character with a wooden leg.

Wooden replacements for legs and feet are among the earliest examples of real, as distinct from imaginary, prosthetic devices. About 440 BCE, the Greek historian Herodotus wrote of the Persian Hegistratus, who was captured by the Spartans and held captive by having his leg locked into a wooden stock. To escape, he amputated part of his foot so that he could pull it through the hole, and later replaced the missing part with a wooden substitute. The Romans also constructed replacements for missing hands, and by medieval times, wooden peg legs or iron hooks had become the standard replacements for missing legs or hands.

There was nothing aesthetically pleasing about peg legs, but they were a simple way to support body weight. The same can be said of a hook in lieu of a hand; it gives limited ability to manipulate objects without matching either the look or the usefulness of a true hand. It was difficult for ancient artificers to make prostheses that both looked the part and acted it, but sometimes, cosmetic appearance and proper functionality could be combined. One of the older prostheses found

by archeologists is Roman and dates to about 300 BCE. Made of bronze and wood, it is modeled to resemble a leg from thigh to calf. Some prosthetic devices, however, were purely cosmetic, such as the metal nose (supposedly made of alloyed gold, silver, and perhaps copper) with which the sixteenth-century Danish astronomer Tycho Brahe replaced his real nose after it was sliced off in a duel. Under the same heading come cosmetic additions and replacements still used today: hair implants for men, breast implants for women, and non-functional glass or plastic eyes for both.

Purely cosmetic replacements are widespread bionic additions that are deeply important to their users, but they offer a lesser challenge than functional prosthetic devices that replicate human abilities. Much of the impetus to make artificial limbs that actually work has come from the needs of injured warriors and soldiers. The knights of medieval Europe in particular had a certain advantage: Their metal armor required the services of armorers, and these artisans were also capable of designing and making functional devices to replace limbs lost in battle. Because knights in armor were already clad in metal, the replacements matched the missing limb in appearance so they worked cosmetically as well.

Some of these knightly prosthetics showed truly advanced features. The most famous example was fashioned for the German knight Götz von Berlichingen, also called Götz mit der Eisernen Hand; that is, Götz with the Iron Hand. Known as a kind of Robin Hood who took the side of peasants against their oppressors, his story was told in the play named after him, written by Johann Wolfgang von Goethe.

Von Berlichingen lost his right hand from a cannon-ball strike at the battle of Landshut in 1504. He had it replaced with an iron prosthesis that featured movable fingers that could be adjusted by his natural hand and locked into place or released through an arrangement of springs. The entire artificial hand could also be set into varied positions. This was not even the first or only such adjustable hand; another with similar characteristics, found near the river Rhine, is thought to date to 1400. A later iron hand and arm, dated about 1602, would look perfectly at home attached to a modern clanker robot. Other

medieval prosthetics were designed for specialized knightly needs, such as an artificial knee built in a semiflexed position that allowed a knight to ride his steed, although it did not support sitting or standing.

Sixteenth-century warfare also motivated the French physician Ambroise Paré to develop innovative procedures that made him a founding figure for modern surgical practice and amputation medicine. His wide experience as an army surgeon gave him ample acquaintance with severe injuries, and he introduced artificial eyes (made of gold and silver) and teeth, and a prosthetic leg. One invention, “Le Petit Lorrain,” was a hand operated by springs that an officer in the French army used in battle.

As in the history of automata, this phase of the development of prosthetics relied on the work of mechanical experts such as armorers and watchmakers, and on the growing knowledge of anatomy. But still the technology was not sufficiently advanced to make devices that were both functional and natural looking, or to make limbs that were easy to use. Iron prosthetics were heavy, and their only source of power was either a natural hand that set and adjusted the artificial unit, or other muscles in the body. Beginning in 1818 and continuing to modern times, inventors have developed harnesses and levers that carry power from other parts of the body, such as the shoulder, to make an artificial hand, say, open and close its grasp.

Natural appearance often had to be sacrificed to functionality, and power to operate a limb was hard to come by. Nevertheless, early inventors improved prosthetic devices through the ingenious use of materials. In 1800, for instance, James Potts of London designed a false limb that came to be known as the “Anglesey Leg,” because it replaced a leg lost by the Marquis of Anglesey at the Battle of Waterloo. Among its advanced features was an articulated foot that could be controlled by catgut strings, extending from knee to ankle, which determined the position of the foot by transmitting motion from the knee. These cablelike control elements have natural parallels; for example, tendons that stretch back to muscles in the arm control the fingers of our hands. Along similar lines, one modern breakthrough is the development of artificial muscles that work like real ones.

More than a century later, around 1912, the English aviator Marcel Desoutter began a trend toward lightness and durability with the introduction of aluminum as a prosthetic material. Although pure aluminum was first extracted in 1827, it was so expensive to produce that it was used mostly in jewelry throughout much of the nineteenth century. But after a cheaper manufacturing method was invented in 1886, aluminum entered industrial use. Its use in aircraft began in 1897 when it was used to form the frame of an airship, and it continued to play an important role in aviation. When Desoutter lost a leg in an airplane accident, he and his brother, an aeronautical engineer, designed the first prosthesis to use aluminum, combining strength with lightness.

While the needs of knightly warriors had provided initial motivation, and advances came from individual efforts like those of Marcel Desoutter, it took the massive scale of modern warfare to truly stimulate prosthetic science. In the American Civil War, the combination of enormous casualties with the state of nineteenth-century medical practice meant that amputations were common—30,000 on the Union side alone. (On the Confederate side, General John Hood had his right leg amputated after he was shot at the battle of Chickamauga in 1863. He finished out the war with a wooden leg that allowed him to continue riding horseback.) When, in 1862, the federal government guaranteed prostheses for Union veterans who had lost limbs, the result was the growth of a business that by 1917 supported some 200 clinics. World War I also had its effect, albeit a relatively limited one in the United States, which was involved in the war only from 1917 to 1918. American soldiers suffered more than 4,000 amputations, compared to nearly 10 times as many for British troops and a total of 100,000 for all the armies from European nations—a number that inspired the growth of prosthetic technology in Europe.

But after World War II, with its extensive casualties among all the combatants (including more than 45,000 amputees among U.S. troops), the need for the serious development of prostheses became widely recognized. Improvements proceeded faster, encouraged by government support. Now, although we do not have a major conflict

on the scale of a world war, prosthetics are still needed to replace limbs lost or amputated through accident and disease. The U.S. population includes more than one million amputees, with an estimated 100,000 lower-limb amputees added yearly. And in some parts of the world, there is a residue of war that maims thousands of people a year—the unexploded land mines strewn around many countries, from Afghanistan to Mozambique. Land mines are cheap and effective weapons, and estimates range up to 100 million of them buried in 62 countries, with Cambodia having one of the densest concentrations. The result is that the business of making prostheses, along with the allied industry of orthotics (limb braces), is estimated to be a $2 billion undertaking worldwide.

This industry has seen significant technological progress. Where metals are used, they are the lightest available, including titanium, but increasingly they are replaced by new materials such as graphite composites like those used in tennis rackets, and plastics, which can be formed into natural-appearing limbs. The mechanical systems that articulate the limbs have also been improved, using pneumatic or hydraulic fittings to provide smooth motion. Some artificial legs are good enough that their wearers can enter athletic events with satisfying performances, such as a time of 12.4 seconds for the 100-meter dash turned in by one runner equipped with a prosthetic leg.

The power sources that move artificial limbs have become more sophisticated as well. Energy-storing artificial feet, designed in the 1980s, incorporate a spring that compresses as the foot strikes the ground, and then extends to release the stored energy and help propel the leg into the next stride forward. Extremely small electric motors have also been developed. Some of them are tiny enough to fit into artificial fingers and hands and powerful enough, for instance, to provide a grasping function, while drawing so little electrical energy that battery operation seems feasible.

However, no matter how effective the engineering and aesthetic design of an artificial arm or leg, it still lacks an important capability. An artificial leg has no sensors to test the nature of the walking surface in order to adjust pace and maintain balance, nor does it receive

commands from a brain that brings in other sensory information such as visual data to forecast changing circumstances. An artificial hand has no sensory feedback that allows the brain to adjust the hand so that it can delicately grasp a teacup without breaking it, or apply full power to twist the cap off a jar. A truly bionic limb needs sensory capability and processing power (in the limb itself, or through connections to the brain) as well as appropriate movement, flexibility, and appearance. In fact, what is needed to make a functional bionic limb for a person is nearly identical to what is needed to make a robotic limb.

This is where digital electronics connects with prosthetic science. Some prosthetic limbs now incorporate electronic sensors and computer chips to make a “smart leg.” A direct neural connection between artificial limb and brain is further off, but here, too, initial results have been obtained, using connected or implanted digital electronics. In a way, the eighteenth-century belief that electricity could invigorate the body and even animate a dead one is becoming realizable in the twenty-first century, through artificial devices that operate electronically—a trend that began when electricity was first introduced into the body.

In the eighteenth century, although electricity was known to stimulate the body, its physiological effects were not studied in detail. Nineteenth-century physicians began experimenting with the influence of electricity on the heart. In 1888, it was found that fibrillation of the heart—that is, the sudden change of a regular beating pattern into an irregular rapid one—could cause sudden death, and in 1899 researchers found that a strong electrical shock could defibrillate an animal’s chaotically beating heart. The first human heart was successfully defibrillated in 1947, and both external and implanted defibrillators were developed in the 1950s and 1960s.

The heart pacemaker is a related and even more helpful bioelectronic device. It sends timed electrical impulses to the heart

muscle, setting a proper rate of beating for people whose hearts beat too slowly. Pacemakers are the most widely used functional bionic implants; some two million have been placed into patients around the world since 1960, including one implanted in U.S. vice president Dick Cheney in 2001. The earliest recorded portable models were developed and demonstrated around 1930, but serious development began only in the 1950s. The history of these devices exemplifies many of the general issues associated with bionic implants, along with their benefits.

To provide the stimulating electrical current, some early pacemaker models used electrodes that lay on the skin but did not enter the body, but these were unsuited for long-term use because they burned the skin after a few days. Other versions developed in the 1950s used implanted wires; that is, the electronic part of the pacemaker was mounted outside the body, from where it sent pulses to a small wire that entered the body and made its way to the heart. But this arrangement, too, had serious drawbacks. It was easy for infection to develop at the entry points of the wires. The external electronic unit that generated the proper pulses was too bulky for easy portability and required so much power that it had to draw on conventional house current. This meant that the implantees’ mobility was limited by the length of power cords, and the implantees were utterly at the mercy of power failures.

These deficiencies have been remedied through parallel advances in electronics and implantation procedures. The problem of infection could be avoided by implanting the entire unit in the body, but that wasn’t possible until the introduction of transistors, which made the units much smaller. As a bonus, the transistorized units also drew less power than the earlier models, so that battery operation became practical. The result was the first wearable battery-powered pacemaker, developed in 1957, and then the first fully implantable unit. The first successful implantation of a pacemaker, in which the unit operated in the implantee for nine months, was carried out in 1960.

Today, further advances in electronics, computation, and implant surgery support highly sophisticated pacemakers. The devices became

programmable in the 1970s; that is, their pulse rates could be externally altered by radio signals without additional surgery. Recent models are rate responsive, meaning they detect the implantee’s activity and adjust the pulse rate accordingly; they work at minuscule power levels, giving them extremely long lifetimes; they operate in a dual-chamber mode, meaning they use two electrical wires to pace both the upper and lower chambers of the heart, synchronizing blood flow for maximum efficiency; and they store the implantee’s medical information in computer memory for retrieval by a physician.

At their high level of perfection, heart pacemakers represent a successful bionic intervention, but they do not involve neural connections. What might be called neurobionics, however, also has a long history arising from the desire to use electricity to affect neural behavior or alleviate certain disabilities. In the Roman era, Scribonius Largus, court physician to the emperor Claudius, reported that he could relieve the pain of headaches by placing a torpedo fish or electric ray—another fish that emits an electric charge—on the sufferer’s forehead. Apparently, just as the fish’s electric charge stunned its prey, the electricity stunned the patient’s nervous system to provide relief. Today electrical stimulation of the nervous system is routinely carried out using both external and implanted devices to relieve pain, and for other therapeutic purposes.

One form of electrical brain stimulation, electroshock or electro-convulsive therapy (ECT), is intended to cure mental disease. The method was conceived when it was seen that epileptic seizures seemed to relieve the symptoms of schizophrenia. By the late 1930s, the Italian researchers Ugo Cerletti and Lucino Bini were learning how to induce such seizures electrically. In initial testing, they placed electrodes so as to send electricity through the entire body of a dog, but the shock to the animal’s heart proved fatal. Placing the electrodes on a dog’s head, however, avoided any flow of current through the heart. In 1938, electroshock was first applied to a schizophrenic person, who

was apparently cured by the procedure, at least for a time. ECT came into heavy use in the 1940s and 1950s, but fell out of favor because of the violent physical convulsions it induced, along with reports of undesirable mental side effects and the possibility of misuse, as dramatically illustrated in the 1975 film One Flew Over the Cuckoo’s Nest. The introduction of alternatives such as psychiatric drug therapy also made the method less desirable. Recently ECT has seen a comeback in treating severe depression, but the method remains controversial.

Electricity can affect the nerves and the brain in subtle and apparently benign ways as well as in overt and violent ones. Electrical stimulation of the vagus nerve, for example, has reduced the frequency of epileptic effects in many patients, although the reasons for this outcome are not entirely understood. The vagus is a complicated, widely distributed nerve (its name comes from a Latin root meaning “wandering”) that runs from the brain stem—which connects the brain to the spinal cord—through the neck and thorax to the abdomen. It has functions related to the ears, tongue, larynx, stomach, and heart. Epilepsy is a chronic disorder of the nervous system, in which seizures arise from excessive interaction among the neurons in the brain. While drugs can reduce that abnormal activity, another possible therapy arose from work dating back to the 1930s, which showed that stimulation of the vagus nerve affects brain activity. In the 1980s, researchers proposed that controlled electrical stimulation of the vagus nerve could desynchronize the brain’s neural signals and hence potentially blunt epileptic effects.

That led to the technique called VNS, vagus nerve stimulation, which has proven beneficial for epileptics whose condition is inoperable and does not respond to drugs. In VNS, an electronic pulser the size of a large coin is implanted under the skin on the left side of the patient’s chest. Every few minutes, the device—powered by a battery with a lifetime of up to five years—generates a series of electrical pulses that lasts a few seconds. The pulses, typically a few thousandths of an ampere, are sent through a wire wrapped around the portion of the vagus nerve running along the left side of the patient’s neck. Patients can also manually activate the device, using a switch operated

by an external magnet, when they feel a seizure coming on. The results have been beneficial; studies show that a year after the device is implanted, nearly a quarter of patients have had their seizure rate reduced 90 percent or more.

A similar implanted device is used to alleviate symptoms of Parkinson’s disease, a chronic and progressive disorder first called the “Shaking Palsy” in 1817 by the English physician James Parkinson. The disease kills certain neurons in the brain that normally produce the chemical dopamine, which transmits nerve signals among areas in the brain that control the muscles. The nerve damage affects body movements at mild to severe levels, with such symptoms as rigid muscles; tremors of the hands, arms, feet, or jaw; changes in speech and handwriting, and the inability to maintain balance. The symptoms can be treated with drugs that replace the missing dopamine, although they do not halt the neural degeneration. A new approach to relieving the muscular symptoms uses a battery-powered implant, which, like the VNS device, generates electrical pulses, although in this case they are sent deep into a particular region of the brain. Originally approved in 1997 by the Food and Drug Administration (FDA), for implantation on one side of the brain to control tremors on that side of the body, FDA approval was extended in 2002 to allow the implantation of dual systems that operate on both sides of the brain.

The electrical pulses used in VNS or the Parkinson’s implant are not digitally encoded, but a more sophisticated type of neural implant does use digital methods to correct another human problem, hearing loss. The physical understanding of sound extends to ancient Greece, where it was realized that sound consists of vibrations in the air. Later, the physiological mechanisms of hearing were explored, illuminating how those vibrations are detected and transmitted in the body. In humans, hearing occurs when sound waves enter the ear canal and set the eardrum vibrating in step with the waves. Those vibrations are transmitted through bony structures to an inner structure called the cochlea. There, the mechanical motion is converted into impulses that travel along the auditory nerves to the brain, where they are analyzed and interpreted to give them meaning.

Earlier methods to improve deficient hearing dealt only with the outer ear. The first approach was the hearing aid, which in early days took the form of an ear horn, a trumpet-shaped device held up to the ear. The ear horn worked like a megaphone or the large hornlike devices seen on Edison’s early phonographs, but in reverse; the large cross-sectional area of the horn captured more sound energy than the ear’s small opening could and funneled that enhanced sound into the ear itself. With the advent of electricity, however, a hearing aid became something different. It changed sound into an electrical signal that was processed and amplified, and then changed back into a louder, clearer sound fed directly into the hearing-impaired ear through a speaker—but still not going directly into the auditory nerves.

Electrical hearing aids were in use by the late nineteenth century. An electrical unit called the Akoulathon, invented in 1898, was being sold commercially in 1901. Like early telephones, it used a carbon “transmitter” or microphone of the type invented in the 1870s. Then, as in the development of computers, advances in electronics—first the vacuum tube that amplified the signals going to the ear, followed by transistors and integrated circuits—led to today’s extremely small and efficient hearing aids.

Today’s hearing aids certainly help those with hearing loss but do not qualify as true bionic additions because they are not directly implanted into the body or connected to its neural system. But help for the hearing-impaired reached bionic status in the late 1950s, when several researchers explored the possibility of direct electrical stimulation of the cochlear nerves. The expectation was that if the nerves were intact, stimulating them directly might produce the sensation of sound in the brain. Considerable development led to the cochlear implant, today’s most mature neural prosthesis—the only one that is commercially available—and the most widespread, with some 30,000 implanted since 1999.

The cochlea—named after the Latin word for “snail”—is a

hollow, fluid-filled structure shaped like a snail shell that resides in the inner ear. Uncoiled, it would stretch well over an inch, but in its natural state it is the size of a pea. Its nearly three full turns contain the nerve endings that make human hearing possible. The process begins when the sound vibrations detected by the eardrum enter the cochlea, where they set internal structures into corresponding vibration. This in turn affects bundles of hairs growing out of sensing units called hair cells. Through a complex mechanical and electrochemical process, the motion of the hairs is converted into electrical signals that travel through the cochlear nerves to the auditory cortex, the part of the brain that interprets the signals as sound.

To perform the artificial equivalent of this natural process, a cochlear implant is surgically embedded in the skull just behind the ear. An external microphone worn behind the ear picks up sound and sends it to a processor, also external. The processor amplifies the sound, filters out extraneous noises, and converts the result into digital electronic impulses that go to a wireless transmitter worn behind the ear, which sends the pulses to a receiver implanted under the skin. The receiver picks up the signals and sends them along wires—up to 24 of them—bundled into a narrow tube that has been woven into the cochlea. There, the digital signals stimulate the auditory nerves to produce neural impulses that are interpreted by the brain as specific sounds. The entire affair is operated by a small battery.

The cochlear implant restores a greater or lesser level of hearing in many deaf implantees. While the sensitivity of the device is too low to allow the listener to hear the very softest sounds, medium- to high-level sounds can be heard. Almost one-third of cochlear implantees hear spoken words clearly enough to use the telephone, and about half of implanted adults who knew how to speak before they lost their hearing can understand at least some words. Even those who do not hear speech clearly can benefit by combining sound cues from the implant with lipreading and other cues to improve their ability to communicate. In many cases, however, these enhancements require brief or sometimes extended training for the benefits to be realized.

Although cochlear implantation is the state of the art in neural

prostheses, it has problems that suggest some general issues in neural implantation. The surgery can produce undesirable side effects: dizziness, because the inner ear is also the organ of bodily balance; infection at the incision site; and occasionally, facial paralysis. Furthermore, the results don’t come anywhere near the quality of natural hearing. Another, subtler, potentially troubling problem for implants in general is a hint of an isolating effect that foretells what truly extensive bodily modifications might entail. Some implantees call the quality of the sound they hear “artificial” or “robotic” and, in a surprising twist, others report that instead of feeling that they have rejoined a world from which they have been cut off, they feel alienated from both the deaf and the hearing communities, with the implants leaving them in limbo without full membership in either world.

Despite these problems, the general success of cochlear implantation suggests how digital implants might correct other human deficiencies, and even extend normal human endowments. If a cochlear implant can turn physical sound into the sensation of sound in a deaf person’s brain, could a retinal implant turn physical light into the sensation of light in a blind person’s brain? Even more interesting, if the implant were sensitive to wavelengths of light that humans ordinarily do not see, such as infrared radiation, could it give a person hypervision?

Similar intriguing questions could be asked about “smart” prosthetic limbs, in which sensors would encode information about a limb’s position in space and the textures it encounters. The information from the sensors would be changed into neural signals and sent to the appropriate part of the brain, which would respond by providing motor signals to the hand or leg to produce fine movement control. Suppose also that motors and power sources are built into the limb, or even that the neural control is extended to a device outside the body such as an exoskeleton or vehicle. The result would be a person with enhanced strength, speed, mobility, or reach.

Along similar lines are what might be called internal prosthetics; that is, replacements for organs such as the heart and the liver. Artificial hearts have received the greatest attention and have steadily

improved, with reduced risks from the implantation process, longer lifetimes once implanted, and a better ability to restore a recipient to something like normal life. Other internal body parts are also under development, and in some cases commercially available, from skin and blood to tiny implanted devices that automatically release insulin for diabetics. If we reach the point where the artificial versions are superior in capacity or lifetime to natural organs, we might realize the dream of extending the human lifespan by bionic means.

As we imagine the Six Million Dollar Human coming into being through these physical prosthetics, we can also imagine mental prosthetics that go beyond merely injecting electronic pulses into the brain. Such enhancements might, for instance, give the brain additional capacity by holding data in an exterior module, retrieving it on command, and recording whatever experiences are worthy of permanent storage. Or they could give the human brain new levels of computing power, or enable direct brain-to-brain or brain-to-machine communication. Another approach might be to use chemical rather than neuroelectronic means to alter brain function. At least one company is developing an implantable chip that contains several hundred minute reservoirs that can be filled with any desired set of drugs, to be dispensed to the body in variable combinations and dosages under microprocessor control. Although the immediate medical purpose of the device is to deliver therapeutic drugs, there is obvious further potential to modify mental acuity, mood, and personality.

These bionic possibilities require technological advances at every level, as I will discuss later in this book, because the obstacles are formidable. For example, despite the improvement offered by cochlear implants, fully replicating human hearing is an enormous task; the current technology activates only a small fraction of the sensors in the inner ear, the 15,000 hair cells in the cochlea. Consider then what it would take to achieve a reasonable artificial version of human vision, which employs 130 million rod and cone sensors in each eye. There are problems with physical implants as well, and not only the difficult issue of linking a synthetic leg to a brain. If they are to break Olympic running records, runners equipped with bionic legs will need power

sources that are more long-lasting, powerful, and compact than present-day batteries.

But to motivated physicians, engineers, and scientists, these barriers are there to be broken, and to them and humanity in general, any technology that eases suffering by repairing or replacing physical damage should be pursued. Nevertheless, there are legitimate questions, including moral issues, about the wisdom and desirability of bionically modifying people. On the purely medical side, the unwanted possibilities include some already noted, such as infections from the implant process and other harmful effects that might develop over time.

Even if we can avoid undesirable physical effects, bionic modifications might have unwanted psychological outcomes or, expressed more poetically, implantation might damage the human spirit. These problematic effects could include a sense of alienation, such as reported by some cochlear implantees, but the jury is still out on this issue because other implantees have not suffered such strong reactions. For example, the journalist David Beresford, whose severe symptoms of Parkinson’s disease have been largely relieved by a neural implant, recently wrote,

Alternatively, unwanted psychological changes might arise from implants that directly impact the brain in the form of neuroelectronic connections or drug-delivery systems that alter emotional states. To the implantee, such reactions would appear as subjective feelings whose effects would be difficult to evaluate by external diagnosis—another complication when weighing the benefits and drawbacks of changing people in this way.

The potential side effects of implantation require long-term study, only now becoming possible, for example, with a new population of

cochlear implantees. Because severe hearing loss can be diagnosed at an early age, cochlear implants have been placed into children as young as 9 to 12 months. These implantees are the first generation to grow up with neurobionic additions, giving researchers the opportunity to better understand the long-term effects of implants and what it means to be bionic. As an example of the problems that might arise, in the summer of 2003, the FDA and the Centers for Disease Control and Prevention presented research showing that children with certain types of cochlear implants are at increased risk of developing a particular form of meningitis. (However, no one knows yet if the implants are responsible, or if children who are good candidates for implantation also happen to be naturally susceptible to the disease.)

Even if bionic additions and implants are proven to be medically and psychologically safe, other questions remain, such as who should have access to the benefits of bionic alteration? If implant technology can extend life, or enhance mental or physical capabilities, how do we decide who receives these precious gifts, and who does not?

The idea that ethical issues might surround bionic modifications, especially cognitive ones, that one might think are purely beneficial, might seem far-fetched. We are not yet, and we might never be, able to modify people sufficiently to change their mental nature. Some researchers believe that artificially enhanced natural minds, and fully synthetic ones, will prove impossible to achieve. This question engages philosophers, psychologists, and cognitive scientists as well as robotics experts: Can we really build artificial brains and link them to artificial bodies? And even harder to answer is the question: If an artificial brain can be built, is the result a self-aware mind, like the one with which we humans experience our own consciousness? The next chapter addresses this complex and perhaps unanswerable question, when we begin to consider artificial beings as they exist today.