The History of Brain Implants

From remote control bulls to bionic eyes

Adam Fitchett
Published in
10 min readJul 30, 2018


It’s a sweltering summer’s day in the city of Córdoba, southern Spain. Spectators have gathered to watch a not unfamiliar site in the Iberian peninsula: a man taunting an enraged bull with a crimson red cape. But as the bull charges towards the man, horns poised to pierce his flesh, something extraordinary happens: the man pushes a button on the device he’s holding in his left hand, and – as if like magic – the bull suddenly loses interest, stops charging, and wanders away.

The spectators present on that day in 1963 bared witness to one of the first demonstrations of direct mind control. The bull was fitted with a brain implant, an electrode array embedded in a part of its brain called the caudate nucleus, which when switched on by the man – Yale University neural engineer, Jose Manuel Rodriguez Delgado – caused the bull to instantly shed all its feelings of aggression. Delgado’s demonstration was a key moment in the history of one of humanity’s most controversial technological endeavours: melding mind and machine with brain implants.

^ A bull charges towards Jose Manuel Rodriguez Delgado. The remote he used to control its brain implant is in his left hand.

The Discovery of Bioelectricity

Humans beings have long been acquainted with the electrical nature of living things. The electric eel (actually a fish, not an eel) can produce a shock of 10 volts with its electric organ, and was first named by zoologist Carl Linnaeus in 1766. In the 1770s, a series of experiments demonstrated that the “torpedo fish” (aka electric ray) delivered its over 200 volt shock by electrical means.

But it was Italian physician Luigi Galvani who first provided evidence that all living things were, in a certain sense, ‘electrical’. On a winter’s day in 1780, Galvani was dissecting a dead frog with a metal scalpel, when the frog’s leg suddenly jerked. Galvani realised that the scalpel had accumulated static electricity, which was able to animate the frog through some kind of internal electrical system. Galvani had discovered the basis of the human nervous system.

^ Drawings by Luigi Galvani, who discovered that frog muscles worked via an electrical system

First forays into neural control

If the brain operated via electricity, that meant it should also be possible to manipulate the movements of a living thing with electrical brain stimulation. German neuroscientists Edward Hitzig and Gustav Frisch became the first researchers to achieve this in 1870, when they stimulated the brain of a dog. The movements produced were highly predictable, suggesting different parts of the cerebral cortex were responsible for different muscles.

But what about human beings? Could our brains also be manipulated in this way? A few years later, American neurosurgeon Roberts Bartholomew provided a resounding “yes”.

One of Bartholomew’s patients, a young woman named Mary Rafferty, had developed an ulceration on her head and eventually a gap in her skull, caused by friction from whalebone in a wig. The surgeon couldn’t pass up this opportunity to gain an ideal test subject; with her consent, he stimulated her exposed brain with electrodes, and saw that “[her] arm was thrown out, the fingers extended, and the leg was projected forward”.

Bartholomew jacked up the current, delivering a much stronger stimulation than before. This time, “her countenance exhibited great distress, and she began to cry…she lost consciousness…succeeded by coma”. Mary awoke from the coma, but died a few days later. It’s not clear to what extent the electrical stimulation did or did not contribute to her death.

Bartholomew’s experiments are a sad and shocking nadir in the history of medical and scientific ethics. But nonetheless, the neurosurgeon provided us with definitive proof that – just like with frogs and dogs – human brains could also be manipulated by electrical stimulation. The groundwork for neural implants had been set.

Fearful monkeys and remote controlled bulls

Jose Manuel Rodriguez Delgado is probably the most controversial figure in the history of brain implants. Not just for the technologies that he built and demonstrated, but also for his views on how those technologies should be used.

In the late 1940s, the lobotomy, an operation in which the frontal lobe of a psychiatric patient is removed or destroyed in order to pacify them, was in vogue on both sides of the Atlantic. A young Delgado wondered whether such damaging surgical interventions could be avoided by designing electrical implants that would achieve the same effect.

Delgado designed compact implantable systems, the size of a large coin, which he implanted in the brains of epilepsy and schizophrenia sufferers who had failed to respond to other kinds of treatment. He also created a “chemitrode” which could release drugs on command into a particular particular part of the brain.

Aside from his famous bull experiment, Delgado carried out many other demonstrations of how a brain implant could be used to alter mood. In one study, he showed how a female macaque could save herself from attack by an aggressive alpha male by pulling a lever that would activate electrodes stimulating his caudate nucleus. In another study, stimulating the brain of a calm, gentle woman sent her into a fit of rage where she smashed her guitar against a wall.

Delgado’s research lead to a public backlash, with fears about the Orwellian implications of the brain stimulation technology. Delgado himself was a keen advocate of using the devices to control human behaviour. Combined with the controversies surrounding lobotomy and electroshock therapy, the backlash was enough to seriously slow down the development of neural interfacing technologies.

^ Delgado and his wife Caroline with a monkey that has been fitted with a brain implant

Making the deaf hear, and the blind see

Amongst all the controversy over remote controlled monkeys and bulls, it’s easy to forget the huge, positive medical achievements that have come from the field of neural interfaces. By far the most successful “neuroprosthetic” ever devised is the cochlear implant, a device which has allowed thousands of deaf people to hear.

The cochlea is a spiral shaped organ found inside the ear which converts sound waves (mechanical signals) to neural impulses (electrical signals), which the brain can then interpret, allowing us to hear. In many deaf people, the tiny hairs in the cochlea that carry out this transduction have become damaged and no longer work.

The first implantable system to directly stimulate the cochlear nerve and bypass the damaged cochlea, thus effectively curing deafnes, was created by American engineers William House and John Doyle in 1961. Today, over 200,000 people around the world have been given the gift of hearing through such a device.

Implants to allow the blind to see have also been created, although progress with these has been much slower than with the cochlear implant. As early as the 1950s, scientists discovered that electrical stimulation of the visual cortex, the part of the brain that interprets visual information, could elicit colourful visual hallucinations called phosphenes. You can see phosphenes yourself if you rub your eyes for a couple of minutes.

The first implantable device designed to stimulate the retina, the light-sensitive part of the eye, was tested in 2002. This device was called the Argus I, and was created by American engineer Robert Greenberg. Although only allowing for the perception of simple shapes, this implant was the first example of an astounding medical achievement, something that would have once been relegated to the category of a miracle.

Earlier this year, engineers at Lausanne’s Federal Institute of Technology unveiled a retinal implant good enough to actually render a blind individual legally non-blind. They boast that the device could allow the user to live a relatively normal life. Developing technologies to restore sight and hearing to disabled individuals is undoubtedly one of the most astounding of humanity’s achievements.

^ The Argus II “bionic eye” (retinal prosthesis), successor to the Argus I, the first retinal prosthetic every tested

Going Deep

Almost everyone knows someone with Parkinson’s Disease (PD). The debilitating motor disorder, which mainly affects the elderly, starts off as a slight tremor in the hands, and eventually progresses to complete paralysis and death. Human beings have triumphed over many natural hurdles, tripling our lifespan over the last few centuries. But this increased lifespan leaves us with the ominous feeling that we all may one day suffer from diseases such as Parkinson’s and Alzheimer’s.

Thankfully, here the field of neural engineering also comes to the rescue. Most PD sufferers are treated with the drug L-dopa, which is converted in the brain to dopamine, the key chemical required to effect motor coordination. However, for some sufferers pharmaceutical treatment is not enough, and a more radical technique is required: deep brain stimulation.

Scientists working with monkey models of PD in the early 1990s discovered that lesioning (i.e. physically destroying) a part of their brain called the subthalamic nucleus (STN) could alleviate the monkeys’ symptoms. They thus reasoned that an artificial lesioning, achieved through electrical inhibition of the neurones in the STN, could achieve the same effect in humans. This was demonstrated in 1995.

Today, thousands of people have been fitted with deep brain stimulation systems to treat not just PD, but also epilepsy, chronic pain, depression and obsessive compulsive disorder. So-called “closed loop” systems have been developed that can detect when a patient requires help, and then deliver the correct stimulation automatically.

The introduction of closed-loop systems has resulted in some interesting findings about human psychology. Our sense of self, while seeming unquestionably real, is more likely to be a kind of illusion constructed by our brain. Users of closed-loop brain stimulation devices sometimes report that the system dissolved their sense of self and agency. This can be deeply troubling for many people, and could pose a significant barrier to the widespread adoption of neural implants.

^ An x-ray of a patient with a deep brain stimulation device

Moving Forward

Deep brain stimulation has been a great success for people with movement coordination issues, but what about paralysed individuals who cannot move at all? For them, a much more impressive technology is required: bionic limbs, integrated with neural interface devices.

In 2000, Brazilian neural engineer Miguel Nicolelis stunned the world when he showed them a monkey that could control a robotic arm with its mind. Eight years later, Nicolelis demonstrated a system where the monkey could use a brain implant control an entire robot walking on a treadmill.

Prosthetic limbs have become increasingly impressive over the last decade. What’s holding back such prosthetics however, is the interface with the nervous system. Most importantly, prosthetic systems currently lack something very important that most of us don’t even realise we have: proprioception.

Proprioception is an internal sense that allows us to orient our limbs with respect to each other. Without it, we would have to stare at our limbs at all times in order to move them correctly. For users of neurally-interfaced prosthetic limbs today, that’s their reality: a painstakingly slow and awkward process, in which every movement must be taken very carefully to avoid slip-ups.

Many engineers are attempting to develop feedback systems that will stimulate the nerves in the leg to create an artificial proprioceptive sense. So far, this approach has proved highly promising, although we’re still a long way from every paralysed person in the world being able to get fitted with such a system.

^ American Les Baugh was fitted with these prosthetic arms in 2014

The Light Fantastic

Since the earliest experiments by Bartholomew and Delgado, brain implants have manipulated neural activity through electrical stimulation. This made a lot of sense, given the electrical nature of the nervous system. However, a new technology called optogenetics could challenge the dominance of this electrical paradigm.

Invented by American engineer Ed Boyden, optogenetics uses light instead of electricity to stimulate and inhibit neurones. Genetic engineering technologies allow light-sensitive channels to be made inside neurones of a particular type. These channels can then be activated by tiny lights implanted in the brain.

While electrical stimulation can be a bit of a sledgehammer-like tool, stimulating large numbers of neurones of various types, optogenetics allows brain stimulation to be much more precise. An optogenetic implant could use different colours of light, combined with different types of light-sensitive channel, to both stimulate and inhibit different kinds of neurone at the same time.

^ A mouse fitted with an optogenetic implant

Will we become cyborgs?

Although today all brain implants are used for medical purposes, to restore lost or absent function to patients, many have speculated about a future in which healthy humans could become cyborgs that use brain implants and other neuroprosthetics to augment their mental and physical faculties.

British engineer Kevin Warwick made waves in 2002 when he had an electrode array implanted in his arm which allowed him to control a robotic hand. Today, there is global community of individuals who call themselves “grinders” or “biohackers” who have augmented themselves with implanted devices such as magnets and RFID chips. In 2017, artist Neil Harbisson had a device fitted that allows him to “hear” colour through vibrations in his skull.

The rare examples notwithstanding, neural implants have so far failed to make a breakthrough as mainstream technologies for healthy individuals. This is partly down to the large risks involved: implantation of a device in the brain can lead to infection or stroke, something that most healthy individuals are not willing to risk to obtain minimal augmentation. Current devices also tend not to be wireless, which restricts everyday functionality.

However, large scale interest in commercialising brain implants has surfaced in recent years. Most notably, entrepreneur Elon Musk, of Tesla and SpaceX fame, has started a company called Neuralink that aims to create flexible brain implants. Musk believes that human beings will be out-paced and possibly dominated by artificial intelligence if we don’t augment ourselves as soon as possible.

Whether or not it is our destiny to become cyborgs, it is clear that with both commercial and medical interest on the rise, brain implants are a technology that will become increasingly prevalent over the next few decades. They could change our lives, and perhaps even change what it means to be human.