For some of the approximately 10 million people worldwide with traumatic brain injury (TBI), forming and holding onto new memories can be one of the hardest things they’ll do in a day. Now imagine a device implanted in the brain that can help them encode memories by means of small electric shocks.
Initial steps toward such a memory neuroprosthetic are being taken at the University of Pennsylvania, where researchers have started tests on brain surgery patients to try to locate, and influence, the processes that control memory formation.
When people suffer brain injuries, several things happen. Neurons might be damaged from the initial impact or from bruising or swelling in the brain afterward. The axons that connect brain regions might be severely jarred during impact, in some cases literally separating from neurons.
The brain is “a complex network of neurons that all have to communicate with each other,” says Matthew Kirschen, a pediatric neurologist at the Children’s Hospital of Philadelphia, who is not involved in the Penn research. “All you need is a little disruption in axonal process and memory is impaired.”
The Pennsylvania team is one of several in the United States that were funded last year by DARPA, the Pentagon research agency, to design and build stimulators that could influence cognition by constantly recording brain function and zapping particular brain areas with low doses of electricity (see “Military Funds Brain-Computer Interfaces to Control Feelings”).
The Penn team, led by cognitive neuroscientist Michael Kahana, has already begun analyzing brain recordings from patients with severe epilepsy. As part of their treatment, these patients receive a small mesh of electrodes under their skulls, which they wear for two to seven weeks. The electrodes collect EEG recordings that are used to calculate where in their brains their seizures are originating, in preparation for surgery to remove the malfunctioning tissue.
While they undergo this treatment, some patients are also volunteering to let Kahana study them as they play memory games on a computer. The EEG electrodes record the average electrical activity of tens of thousands of neurons at once; Kahana says some of the brain waves measured this way are correlated with memory function.
The link between EEG oscillations and memories isn’t clear, but the Penn researchers suspect that certain frequencies could offer a marker for how well a person will remember things. These include so-called theta oscillations—a type of neuronal activity in the hippocampus, one brain region that’s active in creating new memories. “They are the ones [I] think are the most important for memory formation, and they’re often present in the hippocampus,” says Josh Jacobs, a professor of biomedical engineering at Columbia University who is working on the project.
In 2013, researchers at the University of California, Davis, created brain injuries in 56 rats, seriously diminishing their theta oscillations. They then showed that electrically stimulating the medial septal nucleus, part of the hippocampal region in the brain, helped rats escape faster from a maze.
If the Penn team is able to identify markers of memory formation, it will try to influence them by stimulating the brain with low doses of electricity. The goal is to test whether it’s possible to coax the brain’s circuitry into whatever state represents a specific patient’s best possible memory function.
Kahana, who is director of the university’s Computational Memory Lab, says it’s too soon to say whether the idea will work. “We want the brain to exhibit a certain pattern of electrical activity,” he says. “It’s a big leap [to say] we can somehow nudge it into that state by giving it a little push.”
Electrical brain stimulation is already widely used to stop the physical tremors associated with Parkinson’s disease. Although it’s not clear why the technology works, some think it acts to suppress overexcited neurons. About 125,000 people have received deep brain stimulators; nearly all of the devices are manufactured by the Minneapolis medical-device maker Medtronic.
Medtronic’s device uses a wire to stimulate the brain with steady pulses of electricity. The device the Penn researchers hope to eventually build with Medtronic’s help will be different: Jacobs says it will use dozens of electrodes inside the brain to record and stimulate. The set-up could apply current to pass between the electrodes, which can alter the activity of neurons in regions between them. “You could theoretically record and zap quickly to get the memory-encoding circuitry realigned,” says Jacobs.
More than 270,000 members of the U.S. military have been diagnosed with TBI since 2000 ( see “Brain Trauma in Iraq”), according to DARPA, which feels a pressing need for effective treatments, even though most injuries don’t occur in war zones. The Penn team says that it expects to spend two years studying memory signals and another two years developing a device. Clinical tests in humans, Kahana says, could follow if the research is successful.
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