The shape on the screen appears only briefly—just long enough for the test subject to commit it to memory. At the same time, an electrical signal snakes past the bony perimeter of her skull, down through a warm layer of grey matter toward a batch of electrodes near the center of her brain. Zap zap zap they go, in a carefully orchestrated pattern of pulses. The picture disappears from the screen. A minute later, it reappears, this time beside a handful of other abstract images. The patient pauses, recognizes the shape, then points to it with her finger.

What she's doing is remarkable, not for what she remembers, but for how well she remembers. On average, she and seven other test subjects perform 37 percent better at the memory game with the brain pulses than they do without—making them the first humans on Earth to experience the memory-boosting benefits of a tailored neural prosthesis.

If you want to get technical, the brain-booster in question is a “closed-loop hippocampal neural prosthesis.” Closed loop because the signals passing between each patient's brain and the computer to which it's attached are zipping back and forth in near-real-time. Hippocampal because those signals start and end inside the test subject's hippocampus, a seahorse-shaped region of the brain critical to the formation of memories. "We're looking at how the neurons in this region fire when memories are encoded and prepared for storage," says Robert Hampson, a neuroscientist at Wake Forest Baptist Medical Center and lead author of the paper describing the experiment in the latest issue of the Journal of Neural Engineering.

By distinguishing the patterns associated with successfully encoded memories from unsuccessful ones, he and his colleagues have developed a system that improves test subjects’ performance on visual memory tasks. "What we've been able to do is identify what makes a correct pattern, what makes an error pattern, and use microvolt level electrical stimulations to strengthen the correct patterns. What that has resulted in is an improvement of memory recall in tests of episodic memory." Translation: They've improved short-term memory by zapping patients' brains with individualized patterns of electricity.

Today, their proof-of-concept prosthetic lives outside a patient's head and connects to the brain via wires. But in the future, Hampson hopes, surgeons could implant a similar apparatus entirely within a person's skull, like a neural pacemaker. It could augment all manner of brain functions—not just in victims of dementia and brain injury, but healthy individuals, as well.

If the possibility of a neuroprosthetic future strikes you as far-fetched, consider how far Hampson has come already. He's been studying the formation of memories in the hippocampus since the 1980s. Then, about two decades ago, he connected with University of Southern California neural engineer Theodore Berger, who had been working on ways to model hippocampal activity mathematically. The two have been collaborating ever since. In the early aughts, they demonstrated the potential of a neuroprosthesis in slices of brain tissue. In 2011 they did it in live rats. A couple years later, they pulled it off in live monkeys. Now, at long last, they've done it in people.

"In one sense, that makes this prosthesis a culmination," Hampson says. "But in another sense, it's just the beginning. Human memory is such a complex process, and there is so much left to learn. We're only at the edge of understanding it."

To test their system in human subjects, the researchers recruited people with epilepsy; those patients already had electrodes implanted in their hippocampi to monitor for seizure-related electrical activity. By piggybacking on the diagnostic hardware, Hampson and his colleagues were able to record, and later deliver, electrical activity.