We take our hands for granted. Aristotle called the hand “the tool of the tools”, although a hand is a lot more than a mere mechanical appendage. It symbolizes friendship when one “lends a hand” and helplessness when one’s “hands are tied”. We use it to express and explain, to accuse, to bless and to curse. And yet we shamelessly take our hands for granted.
It is true that we don’t know what we have until it’s gone. Losing your hands is the most abject of misfortunes. In 300 B.C., an amputee, if a Stoic, embraced his misery, while others sought help from God. Today, an amputee, if a Stoic, embraces his misery, while others seek help from neurologists.
Neuroprosthetics is exactly what it sounds like: neurologists plant electronics in a patient’s brain that enable one to move a prosthetic, an artificial body part, such as a limb, just by thinking about the action. Even though the discipline is in its infancy, we are sure that it will undoubtedly spur a revolution nature could never have foreseen. However, there’s a catch.
Brain Signal to Machine Output
A hand when moved even voluntarily, feels as though it moved involuntarily. While the process seems instantaneous, it is actually not: the command from the brain takes some time to reach the nerves and therefore the muscles they innervate. They are first fed to the spinal cord, which relays them onto the branches and twigs that constitute your arm.
The commands are electrical, and their ceaseless exchange can be recorded and measured, like any electrical signal, as waves on an oscilloscope. We call the waves they make brain waves. However, what’s astounding is that the brain generates commands and makes brain waves even when there’s no one to listen. Dennis McFarland, a research scientist with the New York State Department of Health’s Wadsworth Center in Albany demonstrated that actual movements and imagined movements result in similar brain activity changes.
An EEG, or electroencephalogram, is a test that records and measures brain signal activity even in patients of stroke-induced paralysis and ALS or Amyotrophic Lateral Sclerosis — what afflicted the eminent cosmologist Stephen Hawking. This was a startling discovery and is the working principle of neuroprosthetics.
Bear in mind that brain signals are essentially electrical signals. What Dennis realized was that one could feed these signals to machines and power them to move, just as the paralyzed person would have previously powered their arms to move. Only if it were that simple. With a dense grid of electrodes attached to their scalp that pulled on dozens of long wires sprawling along the floor, the subjects had to arduously train to control a virtual cursor displayed on a computer screen.
EEG-based neuroprosthetics are no doubt a remarkable achievement, but what vexes neurologists is that they lack resolution. Resolution is one’s ability to distinguish between objects. An EEG-based neuroprosthetic may enable an amputee to control the entire hand, but only the hand in its entirety, not its individual fingers. Paper glasses and eggs don’t stand a chance against such binary, “open and shut” hands.
The embarrassing lack of dexterity is a result of the distance between the electrodes and cortex: the part of the brain that dictates our movements or motor functions. In an EEG-based neuroprosthetic, the electrode and cortex are separated by first skin, then bone, and then tissues and membranes. The signals then received by the electrodes are not very rich. This hindrance restricts EEG-based neuroprosthetics to what one might deem as “simpler” tasks, such as selecting alphabets for communication devices.
To obtain richer signals, electrodes must be planted much deeper or much closer to the cortex. This is achieved by Electrocorticography (ECoG). ECoG overcomes the limitations of EEG by measuring brain activity from the cortex’s surface. To implement this, electrodes are surgically implanted.
ECoG is effective to the extent that subjects acquire control of the virtual cursor in mere minutes! The result reflects an astonishing increase in resolution. This increase makes, say, the artificial hand more dexterous, but not as dexterous as a natural hand is: while by virtue of elaborate technology, the hand can hold paper glasses and eggs, it still cannot operate on the scale of individual fingers. To operate on the scale of fingers, we must, like someone looking for pearls, dive even deeper and procure the richest signals. However, when you go so deep, things get spooky.
If someone with an artificial arm were to be blindfolded and asked to differentiate with her arm between rubber and wood, would she be able to do it? Today, it is highly unlikely. The prevalent technology is unidirectional: signals flow from the brain to the arm, however, not from the arm and back to the brain. An absence of feedback renders the amputee devoid of sensation.
Yet again we find ourselves taking our hands for granted. People assisted by neuroprosthetics crave sensation. They are deprived of texture, temperature, vibration, pain, shape and every other sensation we pay heed to only when a convincing writer asks us to. They’re filled with rapture even at the thought of regaining, not even the entire gamut, but perhaps the tiniest share. A lack of feedback impairs utility as well: it makes for clumsy and inefficient movements and grasps. It is the lack of sensation that, despite a prosthetic’s obvious utility, like a pirate’s hook only more sophisticated, it will never be perceived as “natural”.
Sensations are so important because they shape perception. In this regard, neuroprosthetics entail and present us with a variety of conundrums: could a prosthetic eye unleash in a blind person the same nuances of imagery a sunset unleashed in John Cheever? Could the beholder also see “gold, brass, cauldrons, streaks of lemon yellow and then, unexpectedly, a field of roses”? However, a technology so bewildering and revolutionary also paves the way for dystopian fantasies: could parents in the future, with a remote, control and direct the thoughts of their children who were implanted with electrodes at birth, as they please? Could governors do the same to the governed?
Obtaining the richest signal might have the fortuitous effect of reviving sensations. To obtain them we must measure signals at the scale of individual neutrons. The catch is that neurons are so inextricably tangled that stimulating one will indiscriminately disturb the others beside it. Uncertainty is then inevitable: the thought of moving one finger will unintentionally move another. Even the thinnest and sharpest pin in the universe cannot achieve this: there are more neuronal connections in a cubic centimeter of our brain than there are stars in our galaxy. We currently believe it is this inscrutable complexity that is responsible for consciousness, for what neurologists call qualia: the “experience” of enticing red or boring gray.
At the rate that technologies are currently shrinking, one shouldn’t be surprised if engineers do build a processor small enough to stimulate, if not a single neuron, then at least a patch of neurons. However, this has its own disadvantages and advantages. The immune system frowns upon the introduction of foreign objects in our body. When electrodes are planted for prolonged periods, their conductivity gradually declines as their interfaces become scarred. The insulated electrodes make for poor measurements. This is where neuroprosthetics bring numerous disciplines under the same umbrella: other than neuroscientists, computer scientists and electronic engineers, material engineers are now sought to develop new substrates that might be immune to corrosion.
The development of such a substrate will be a blessing for people suffering from spinal cord injuries. This is the major advantage of stimulating neurons. With the highway and road network now irreparably damaged, the sensations can directly “teleport” to their destinations. Directly stimulating neurons renders the spinal cord redundant. Naturally, this is extremely difficult, but there’s a way out. Either we find the necessary signals, or we relearn how we feel.
In a study conducted by Sliman Bensmaia, a neuroscientist at the University of Chicago, researchers repeatedly poked monkeys in two spots on one hand and trained the primates to move their eyes left or right, depending on whether the second poke was made to the left or right of the first one. The researchers then planted electrodes in the monkeys’ brains and determined the parts of their brain that were stimulated as they poked the different spots.
After successfully mapping the parts, the researchers stimulated the neurons occupying these parts by passing a current through the electrodes. Surprisingly and yet unsurprisingly, this simulated a poke. And yes, in response, the monkeys moved their eyes as though their hands had actually been poked! Bensmaia reported the results at the Society for Neuroscience’s 2012 meeting in New Orleans, Louisiana.
Such a test has only been conducted on monkeys. In fact, monkeys have been trained to play video games simply by thinking about the actions involved. Human brains are much denser and therefore much more difficult to map so scrupulously, neuron by neuron. Today, resolution and sensation are compensated for by technology. Mechanical transducers convert pressure signals generated by the fingers into electrical signals, thereby simulating, if not the “experience”, then at least the sensation of touch. Hopefully, future innovations will enable us to simulate experience as well.
If you think experiences simulated by electrical signals aren’t “authentic”, let me remind you that your experiences or memories of, say, your first day of school, or your child’s first day of school, or your first love or well, rejection, aren’t any different. The experiences you profoundly cherish, the indescribable qualia, your perception, your memories, your very identity can be reduced to nothing more than a unique combination of molecules that incessantly interact with each other.
“Essentially, all experiences of human nature ever produced,” says scientist and physician Miguel Nicotelis, a pioneer in neuronal population coding, “from a caveman’s paintings to Mozart’s symphonies and Einstein’s view of the universe, emerge from the same source: the relentless dynamic toll of large populations of interconnected neurons.”
Are we then, as Gregory House acerbically remarks, “just a bag of chemicals?” This reminds me of another conundrum: If I were to disintegrate your body into its molecules and replicate on Mars whatever unique combination of them constitutes you, would you and your “replica” be the same person? Would the process feel just like waking up from a long, deep sleep? And if it is really you, at what point of integrating the molecules did the replica become you? Who would the replica be before it became you? At what point in its short course, we wonder, does an electrical signal traveling from our sensory organs to our brain become a ravishing, unforgettable experience?