What would you give for a retinal chip that let you see in the dark or for a next-generation cochlear implant that let you hear any conversation in a noisy restaurant, no matter how loud? Or for a memory chip, wired directly into your brain’s hippocampus, that gave you perfect recall of everything you read? Or for an implanted interface with the Internet that automatically translated a clearly articulated silent thought (“the French sun king”) into an online search that digested the relevant Wikipedia page and projected a summary directly into your brain?

Science fiction? Perhaps not for very much longer. Brain implants today are where laser eye surgery was several decades ago. They are not risk-free and make sense only for a narrowly defined set of patients--but they are a sign of things to come.

Unlike pacemakers, dental crowns or implantable insulin pumps, neuroprosthetics--devices that restore or supplement the mind’s capacities with electronics inserted directly into the nervous system--change how we perceive the world and move through it. For better or worse, these devices become part of who we are.

Neuroprosthetics aren’t new. They have been around commercially for three decades, in the form of the cochlear implants used in the ears (the outer reaches of the nervous system) of more than 300,000 hearing-impaired people around the world. Last year, the Food and Drug Administration approved the first retinal implant, made by the company Second Sight.

Both technologies exploit the same principle: An external device, either a microphone or a video camera, captures sounds or images and processes them, using the results to drive a set of electrodes that stimulate either the auditory or the optic nerve, approximating the naturally occurring output from the ear or the eye.

Another type of now-common implant, used by thousands of Parkinson’s patients around the world, sends electrical pulses deep into the brain proper, activating some of the pathways involved in motor control. A thin electrode is inserted into the brain through a small opening in the skull; it is connected by a wire that runs to a battery pack underneath the skin. The effect is to reduce or even eliminate the tremors and rigid movement that are such prominent symptoms of Parkinson’s (though, unfortunately, the device doesn’t halt the progression of the disease itself). Experimental trials are now under way to test the efficacy of such “deep brain stimulation” for treating other disorders as well.

Electrical stimulation can also improve some forms of memory, as the neurosurgeon Itzhak Fried and his colleagues at the University of California, Los Angeles, showed in a 2012 article in the New England Journal of Medicine. Using a setup akin to a videogame, seven patients were taught to navigate a virtual city environment with a joystick, picking up passengers and delivering them to specific stores. Appropriate electrical stimulation to the brain during the game increased their speed and accuracy in accomplishing the task.

But not all brain implants work by directly stimulating the brain. Some work instead by reading the brain’s signals--to interpret, for example, the intentions of a paralyzed user. Eventually, neuroprosthetic systems might try to do both, reading a user’s desires, performing an action like a Web search and then sending the results directly back to the brain.

How close are we to having such wondrous devices? To begin with, scientists, doctors and engineers need to figure out safer and more reliable ways of inserting probes into people’s brains. For now, the only option is to drill small burr-holes through the skull and to insert long, thin electrodes--like pencil leads--until they reach their destinations deep inside the brain. This risks infection, since the wires extend through the skin, and bleeding inside the brain, which could be devastating or even fatal.

External devices, like the brainwave-reading skull cap made by the company NeuroSky (marketed to the public as “having applications for wellness, education and entertainment”), have none of these risks. But because their sensors are so far removed from individual neurons, they are also far less effective. They are like Keystone Kops trying to eavesdrop on a single conversation from outside a giant football stadium.

Today, effective brain-machine interfaces have to be wired directly into the brain to pick up the signals emanating from small groups of nerve cells. But nobody yet knows how to make devices that listen to the same nerve cells that long. Part of the problem is mechanical: The brain sloshes around inside the skull every time you move, and an implant that slips by a millimeter may become ineffective.

Another part of the problem is biological: The implant must be nontoxic and biocompatible so as not to provoke an immune reaction. It also must be small enough to be totally enclosed within the skull and energy-efficient enough that it can be recharged through induction coils placed on the scalp at night (as with the recharging stands now used for some electric toothbrushes).

These obstacles may seem daunting, but many of them look suspiciously like the ones that cellphone manufacturers faced two decades ago, when cellphones were still the size of shoeboxes. Neural implants will require even greater advances since there is no easy way to upgrade them once they are implanted and the skull is sealed back up.

But plenty of clever young neuro-engineers are trying to surmount these problems, like Michel Maharbiz and Jose Carmena and their colleagues at the University of California, Berkeley. They are developing a wireless brain interface that they call “neural dust.” Thousands of biologically neutral microsensors, on the order of one-tenth of a millimeter (approximately the thickness of a human hair), would convert electrical signals into ultrasound that could be read outside the brain.

The real question isn’t so much whether something like this can be done but how and when. How many advances in material science, battery chemistry, molecular biology, tissue engineering and neuroscience will we need? Will those advances take one decade, two decades, three or more? As Dr. Maharbiz said in an email, once implants “can be made ‘lifetime stable’ for healthy adults, many severe disabilities…will likely be chronically treatable.” For millions of patients, neural implants could be absolutely transformative.

Assuming that we’re able to clear these bioengineering barriers, the next challenge will be to interpret the complex information from the 100 billion tiny nerve cells that make up the brain. We are already able to do this in limited ways.

Based on decades of prior research in nonhuman primates, John Donoghue of Brown University and his colleagues created a system called BrainGate that allows fully paralyzed patients to control devices with their thoughts. BrainGate works by inserting a small chip, studded with about 100 needlelike wires--a high-tech brush--into the part of the neocortex controlling movement. These motor signals are fed to an external computer that decodes them and passes them along to external robotic devices.

Almost a decade ago, this system was used by a tetraplegic to control an artificial hand. More recently, in a demonstration of the technology’s possibilities that is posted on YouTube, Cathy Hutchinson, paralyzed years earlier by a brainstem stroke, managed to take a drink from a bottle of coffee by manipulating a robot arm with only her brain and a neural implant that literally read (part of) her mind.

For now, guiding a robot arm this way is cumbersome and laborious, like steering a massive barge or an out-of-alignment car. Given the current state of neuroscience, even our best neuroscientists can read the activity of a brain only as if through a glass darkly; we get the gist of what is going on, but we are still far from understanding the details.

In truth, we have no idea at present how the human brain does some of its most basic feats, like translating a vague desire to return that tennis ball into the torrent of tightly choreographed commands that smoothly execute the action. No serious neuroscientist could claim to have a commercially ready brain-reading device with a fraction of the precision or responsiveness of a computer keyboard.

In understanding the neural code, we have a long way to go. Advances in molecular biology, neuroscience and material science are almost certainly going to lead, in time, to implants that are smaller, smarter, more stable and more energy-efficient. These devices will be able to interpret directly the blizzard of electrical activity inside the brain. For now, they are an abstraction, something that people read about but are unlikely to experience for themselves. But someday that will change.

Eventually neural implants will make the transition from being used exclusively for severe problems such as paralysis, blindness or amnesia. They will be adopted by people with less traumatic disabilities. When the technology has advanced enough, implants will graduate from being strictly repair-oriented to enhancing the performance of healthy or “normal” people. They will be used to improve memory, mental focus (Ritalin without the side effects), perception and mood (bye, bye Prozac).

Many people will resist the first generation of elective implants. There will be failures and, as with many advances in medicine, there will be deaths. But anybody who thinks that the products won’t sell is naive. Even now, some parents are willing to let their children take Adderall before a big exam. The chance to make a “superchild” (or at least one guaranteed to stay calm and attentive for hours on end during a big exam) will be too tempting for many.

Even if parents don’t invest in brain implants, the military will. A continuing program at Darpa, a Pentagon agency that invests in cutting-edge technology, is already supporting work on brain implants that improve memory to help soldiers injured in war. Who could blame a general for wanting a soldier with hypernormal focus, a perfect memory for maps and no need to sleep for days on end? (Of course, spies might well also try to eavesdrop on such a soldier’s brain, and hackers might want to hijack it. Security will be paramount, encryption de rigueur.)

An early generation of enhancement implants might help elite golfers improve their swing by automating their mental practice. A later generation might allow weekend golfers to skip practice altogether. Once neuroscientists figure out how to reverse-engineer the end results of practice, “neurocompilers” might be able to install the results of a year’s worth of training directly into the brain, all in one go.

That won’t happen in the next decade or maybe even in the one after that. But before the end of the century, our computer keyboards and trackpads will seem like a joke; even Google Glass 3.0 will seem primitive. Why would you project information onto your eyes (partly occluding your view) when you could write information into your brain so your mind can directly interpret it? Why should a computer wait for you to say or type what you mean rather than anticipating your needs before you can even articulate them?

By the end of this century, and quite possibly much sooner, every input device that has ever been sold will be obsolete. Forget the “heads-up” displays that the high-end car manufactures are about to roll out, allowing drivers to see data without looking away from the road. By the end of the century, many of us will be wired directly into the cloud, from brain to toe.

Will these devices make our society as a whole happier, more peaceful and more productive? What kind of world might they create?

It’s impossible to predict. But, then again, it is not the business of the future to be predictable or sugarcoated. As President Ronald Reagan once put it, “The future doesn’t belong to the fainthearted; it belongs to the brave.”

The augmented among us--those who are willing to avail themselves of the benefits of brain prosthetics and to live with the attendant risks--will outperform others in the everyday contest for jobs and mates, in science, on the athletic field and in armed conflict. These differences will challenge society in new ways--and open up possibilities that we can scarcely imagine.

Dr. Marcus is professor of psychology at New York University and often blogs about science and technology for the New Yorker. Dr. Koch is the chief scientific officer of the Allen Institute for Brain Science in Seattle.