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In a five-year, $77 million project by the Department of Defense to create an implantable brain device that restores memory-generation capacity for people with traumatic brain injuries, a device has now been developed by Michael Kahana, a professor of psychology at the University of Pennsylvania, and the medical technology company Medtronic Plc, and successfully tested with funding from America’s Defense Advanced Research Projects Agency (Darpa).

Connected to the left temporal cortex, it monitors the brain’s electrical activity and forecasts whether a lasting memory will be created. “Just like meteorologists predict the weather by putting sensors in the environment that measure humidity and wind speed and temperature, we put sensors in the brain and measure electrical signals,” Kahana says. If brain activity is suboptimal, the device provides a small zap, undetectable to the patient, to strengthen the signal and increase the chance of memory formation.

In two separate studies, researchers found the prototype consistently boosted memory 15 per cent to 18 per cent. The second group performing human testing, a team from Wake Forest Baptist Medical Center in Winston-Salem, N.C., aided by colleagues at the University of Southern California, has a more finely tuned method. In a study published last year, their patients showed memory retention improvement of as much as 37 per cent. “We’re looking at questions like, ‘Where are my keys? Where did I park the car? Have I taken my pills?’â” says Robert Hampson, lead author of the 2018 study…

Both groups have tested their devices only on epileptic patients with electrodes already implanted in their brains to monitor seizures; each implant requires clunky external hardware that won’t fit in somebody’s skull. The next steps will be building smaller implants and getting approval from the U.S. Food and Drug Administration to bring the devices to market… Justin Sanchez, who just stepped down as director of Darpa’s biological technologies office, says veterans will be the first to use the prosthetics. “We have hundreds of thousands of military personnel with traumatic brain injuries,” he says. The next group will likely be stroke and Alzheimer’s patients.

Eventually, perhaps, the general public will have access—though there’s a serious obstacle to mass adoption. “I don’t think any of us are going to be signing up for voluntary brain surgery anytime soon,” Sanchez says. “Only when these technologies become less invasive, or noninvasive, will they become widespread.”