Healthy brains turn sensory input into memories by sending electrical signals through several regions of the memory center, known as the hippocampus. The process is kind of like a game of telephone: when a signal reaches each region, it's re-encoded, so once it reaches its final destination it's a completely different signal than it was at the beginning of the journey. But when there's damage somewhere in the hippocampus, that signal can fail to reach its destination, preventing the memory from forming. That's why people with ailments that affect this area of the brain often can't make new memories, even though they can still recall events from before their brain was damaged.

Back in 2015, researchers at University of Southern California and Wake Forest Baptist Medical center announced that they had successfully mimicked this signal journey to create a memory-restoring "brain prosthesis." To test its effectiveness, the team recruited nine people with epilepsy who were already scheduled to have electrodes implanted into their brains to treat chronic seizures, since adding one more electrode wouldn't be much of a burden.

With the memory electrode implanted, they had patients make new memories while the team "read" the electrical signals created by their brains at two different regions of the hippocampus. Next, they fed those signals into the computer model they had created to mimic the memory-making process, and watched how it translated signals from one region into signals in the next region, as compared with the way the patients' brains actually did it. Over hundreds of trials, the model accurately predicted how the signals would be translated with about 90 percent accuracy.

That 2015 study just showed it was possible. The next step was to prove that it worked. To do that, the team recruited 20 more epilepsy patients to have the electrode implanted in their brains. Next, they recorded the signals in their brains as they performed memory exercises, a lot like they had in the previous study. Then they had the patients do another memory test, except this time they sent specially designed electric signals through the hippocampus in about a third of the exercises.

Over all of the patients, that brain stimulation resulted in an average 15 percent improvement in short-term memory and 25 percent in working memory. Just to make sure it was the computer model and not the electricity alone that helped, they also tried the test with random bursts of electricity. That made memory recall worse, not better, showing that it really was their design that made it happen.

This is primarily aimed at people with severe memory problems — after all, it's a pretty invasive surgery for someone who just wants help remembering people's names at parties — but it's possible this technology could be used for other brain ailments as well. Studying the brain signals generated in vision or movement, for instance, might make a brain prosthesis possible for those skills, too.

To examine how memory can fail you, check out "The Memory Illusion: Why You May Not Be Who You Think You Are" by research psychologist Julia Shaw. The audiobook is free with a 30-day trial of Audible. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.