Scientists Zap Sleeping Humans’ Brains With Electricity To Improve Memory

A little brain stimulation at night seems to help people remember what they learned the night before.

A study of 18 people with severe epilepsy found they performed better on a memory test if they received deep brain stimulation while they slept, a team reports in the review Natural neuroscience.

Stimulation was delivered for no REM sleep, when the brain is believed to be reinforcing memories that it intends to use in the future. It was designed to synchronize the activity of two brain areas involved in memory consolidation: the hippocampus and the prefrontal cortex.

“Some have improved by 10% or 20%, others by 80%”, depending on the level of synchronization, explains Dr Itzhak Friedstudy author and professor of neurosurgery at the University of California, Los Angeles.

The findings support a cutting-edge theory of how the brain transforms an everyday event into a memory that can last for days, weeks, or even years. They also suggest a new approach to help people with various sleep and memory problems.

“We know for example that in patients with dementia, Alzheimer’s, sleep doesn’t work very well at all,” says Fried. “The question is whether by changing the architecture of sleep you can help memory.”

Although the results come from a small study of people with a specific disorder (epilepsy), they are “a cause for celebration”, says Dr Gyorgy Buzsakiprofessor of neuroscience at New York University who was not involved in the research.

Rhythms in the brain

During sleep, brain cells activate in rhythmic patterns. Scientists believe that when two areas of the brain synchronize their triggering patterns, they are able to communicate.

Studies suggest that during non-REM sleep, the hippocampus, located deep in the brain, synchronizes its activity with the prefrontal cortex, which sits just behind the forehead. This process seems to help transform the memories of the day into memories that can last a lifetime.

Fried and his team therefore wanted to know if increasing the synchronization between the two areas of the brain could improve a person’s memory of facts and events.

Their study involved patients with epilepsy who already had electrodes in their brains as part of their medical evaluation. This gave scientists a way to monitor and modify a person’s brain rhythms.

They measured memory using a “celebrity pet” test in which participants saw a series of images that matched a particular celebrity with a specific pet. The goal was to remember which animal went with which celebrity.

The patients viewed the images before going to bed. Then, while they slept, some of them received tiny electrical impulses through their brain wires.

“We were measuring activity in a deep area of ​​the brain [the hippocampus]and then, on this basis, we stimulated in a different field [the prefrontal cortex]”, says Fried.

In the patients who received the stimulation, the rhythms in the two areas of the brain became more synchronized. And when those patients woke up, they did better on the celebrity test.

The findings back decades of animal research showing the importance of rhythm and synchrony in forming long-term memories.

“If you want to talk to the brain, you have to talk to it in its own language,” says Buzsaki.

But altering the rhythms in a healthy person’s brain might not improve their memory, he says, because those communication channels are already optimized.

Epilepsy patients may have improved because they started out with sleep and memory problems caused by both the disorder and the medications used to treat it.

“Maybe what happened here just makes the worst memories better,” Buzsaki said.

Even so, he says, the approach has the potential to help millions of people with memory problems. And brain rhythms probably play an important role in many other problems.

“They’re not memory-specific. They do a lot of other things,” Buzsáki says, like regulating mood and emotions.

So adjusting brain rhythms could also help treat conditions like depression, he says.

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