Chances are you have never heard of the neural code. And yet, from both a practical and philosophical perspective, the neural code is  the most important remaining scientific mystery. Analogous to the machine code of a digital computer, the neural code is the software, set of rules, syntax, that transforms electrical pulses in the brain into perceptions, memories, decisions. A solution to the neural code could – in principle – give us almost unlimited power over our psyches, because we could monitor and manipulate brain cells with exquisite precision by speaking to them in their own private language.

The neural code is such a dauntingly complex, technical topic – overlapping with nonlinear dynamics, information theory, and other esoteric fields – that it receives little publicity beyond  specialized journals. Moreover, until recently a complete decoding of the brain seemed impossibly remote, because researchers had limited means of probing the microcircuitry of living brains. Trying to glean the neural code with external scanning methods such as magnetic - resonance imaging or electroencephalography is like trying to learn English by standing outside a baseball stadium and listening to the roar of the crowd. But just in the past decade researchers have begun crafting arrays of microelectrodes that can eavesdrop on hundreds and even thousands of separate neurons simultaneously, and they have acquired ever-more-powerful computers and algorithms for analyzing data.

The immediate goal of many neural-code researchers is producing “neural prostheses” for the disabled. By far the most successful neural prosthesis is the artificial cochlea. More than 80,000 people have been equipped with these devices, which restore at least rudimentary hearing by feeding signals from an external microphone to the auditory nerve. Work on other prostheses is proceeding more slowly. Artificial retinas, light-sensitive chips that mimic the eye’s signal-processing ability and stimulate the optical nerve or visual cortex, have been tested in a handful of blind subjects, but they usually “see” nothing more than phosphenes, or bright spots.

Several groups have recently shown that monkeys can control computers  and robotic arms “merely by thinking,” as media accounts invariably  put it – not telekinetically but via implanted electrodes picking up  neural signals. The potential for empowering the paralyzed is obvious, but so far only a few experiments with humans have been carried out, with limited success. A program to create chips that can restore the memory of those afflicted with Alzheimer’s disease or other disorders is still a year or two away from testing in rats.

The National Institutes of Health and the Defense Advanced Research  Projects Agency (DARPA) nonetheless see enough promise in this  research to pump millions into it every year. darpa is less interested in treating the disabled than in enhancing the cognitive capacities of healthy soldiers. DARPA officials have broached the prospect of cyborg warriors downloading complex fighting procedures directly into their brains, like the heros of The Matrix; controlling jets with their thoughts, like Clint Eastwood in the old flick Firefox; or being remotely controlled, like the assassin in the recent remake of The Manchurian Candidate. “Implanting electrodes into healthy people is not something we’re going to do any time soon,” a DARPA official told me recently. “But 20 years ago, no one would have thought we’d put a laser in the eye either. So this is an agency that leaves the door open to what’s possible.”

Beyond these bionic possibilities, neural-code research could have a  dramatic impact on artificial intelligence, which has thus far failed to deliver on its promise of creating truly intelligent machines. If  the brain’s programming tricks can be transferred to computers and  robots, they may finally become as clever as HAL in 2001 and C3PO in Star Wars. In perhaps the most fantastic scenario of all, long envisioned by AI mavens such as Marvin Minsky and Ray Kurzweil, mastery of the neural code might allow us to transform our psyches into software programs – strings of ones and zeros – that can be downloaded into machines, where we will live forever in cyberspace.

Finally, the neural code could represent the key to one of  philosophy’s oldest and deepest conundrums – the mind-body problem – in the following way: all codes involve the transformation of purely physical phenomena – the positioning of base pairs in a dna strand, the flow of electrons in a computer, the scratch of a pen on paper – into information, which transcends the physical realm. By revealing how the brain transforms a physical process such as the firing of a neuron into information and even meaning, another non-physical phenomena, the neural code may reveal how mere matter becomes a mind. Who knows? Maybe we’ll even solve the riddle of free will. We may finally understand how this wrinkled lump of jelly in our skulls generates a unique self with a sense of personal identity and autonomy, a self that perceives, emotes, remembers, imagines, chooses, acts, creates.

Neuroscientists are still far from converging on a solution to the neural code. They are embroiled in debates over whether informationis represented primarily by signals from individual neurons, by many neurons firing in lockstep, by even higher-level waves of chaotic electrical activity sweeping through the brain, or all of the schemes above and more. These disputes have led some theorists to warn that the neural code may never be fully deciphered. But 60 years ago, some biologists feared the genetic code was too complex to crack. Then in 1953 Francis Crick and James Watson unraveled the structure of DNA, and researchers quickly established that the double helix mediates an astonishingly simple genetic code governing the heredity of all organisms.

Science’s success in deciphering the genetic code, which has  culminated in the Human Genome Project, has been widely acclaimed – and with good reason, because knowledge of our genetic makeup could allow us to reshape our fundamental nature. A solution to the neural code could, in principle, give us much greater, more direct control over ourselves than mere genetic manipulation. It is not too soon to start pondering the potential consequences of this achievement. How will knowledge of the neural code be used, and by whom? Who will be liberated, and who enslaved?

John Horgan, former senior writer at Scientific American, is author of, most recently, Rational Mysticism: Spirituality Meets Science in  the Search for Enlightenment.