Memory Implants
A maverick neuroscientist believes he has deciphered the code by which the brain forms long-term memories.
Theodore Berger, a biomedical engineer and neuroscientist at the University of Southern California in Los Angeles, envisions a day in the not too distant future when a patient with severe memory loss can get help from an electronic implant. In people whose brains have suffered damage from Alzheimer’s, stroke, or injury, disrupted neuronal networks often prevent long-term memories from forming. For more than two decades, Berger has designed silicon chips to mimic the signal processing that those neurons do when they’re functioning properly—the work that allows us to recall experiences and knowledge for more than a minute. Ultimately, Berger wants to restore the ability to create long-term memories by implanting chips like these in the brain.
The idea is so audacious and so far outside the mainstream of neuroscience that many of his colleagues, says Berger, think of him as being just this side of crazy. “They told me I was nuts a long time ago,” he says with a laugh, sitting in a conference room that abuts one of his labs. But given the success of recent experiments carried out by his group and several close collaborators, Berger is shedding the loony label and increasingly taking on the role of a visionary pioneer.
Berger and his research partners have yet to conduct human tests of their neural prostheses, but their experiments show how a silicon chip externally connected to rat and monkey brains by electrodes can process information just like actual neurons. “We’re not putting individual memories back into the brain,” he says. “We’re putting in the capacity to generate memories.” In an impressive experiment published last fall, Berger and his coworkers demonstrated that they could also help monkeys retrieve long-term memories from a part of the brain that stores them.
If a memory implant sounds farfetched, Berger points to other recent successes in neuroprosthetics. Cochlear implants now help more than 200,000 deaf people hear by converting sound into electrical signals and sending them to the auditory nerve. Meanwhile, early experiments have shown that implanted electrodes can allow paralyzed people to move robotic arms with their thoughts. Other researchers have had preliminary success with artificial retinas in blind people.
Still, restoring a form of cognition in the brain is far more difficult than any of those achievements. Berger has spent much of the past 35 years trying to understand fundamental questions about the behavior of neurons in the hippocampus, a part of the brain known to be involved in forming memory. “It’s very clear,” he says. “The hippocampus makes short-term memories into long-term memories.”
What has been anything but clear is how the hippocampus accomplishes this complicated feat. Berger has developed mathematical theorems that describe how electrical signals move through the neurons of the hippocampus to form a long-term memory, and he has proved that his equations match reality. “You don’t have to do everything the brain does, but can you mimic at least some of the things the real brain does?” he asks. “Can you model it and put it into a device? Can you get that device to work in any brain? It’s those three things that lead people to think I’m crazy. They just think it’s too hard.”
