Sleep Science

Deep-Brain Stimulation May Strengthen Your Memories While You Sleep

Electrical stimulation during a stage of sleep called deep sleep appeared to boost interactions between two brain areas involved in memory.

Bright Iridescent Human Brain of Holographic Paper Craft on Purple Background.
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Every night, when your head hits the pillow, you do more than just dream. Your brain takes all the information experienced that day — formulas crammed for a calculus test, snippets of office gossip, random facts from a celebrity interview — and churns it into memories stored away in our neural hard drives for (hopefully) later use.

This process of nightly record-keeping typically involves two brain regions: the hippocampus, doing most of the upfront work of temporarily storing fresh information, and the neocortex, learning from the hippocampus what memories to keep in long-term storage.

That’s at least been the working theory of systems-level memory consolidation based on rodent and indirect studies of the human brain. But now a group of researchers led by the University of California, Los Angeles Health found direct physiological evidence of exactly how the hippocampus and neocortex partner up to encode and reinforce memories during the third stage of non-rapid eye movement (NREM) sleep called deep or slow-wave sleep. These scientists also found that when you zap your brain during this phase with what’s called deep-brain stimulation, the boost in electricity also appears to boost memory. It’s a finding that adds to a growing body of evidence in support of brain stimulation technology in improving cognitive function.

“This provides the first major evidence down to the level of single neurons that there is indeed this mechanism of interaction between the memory hub and the entire cortex,” Itzhak Fried, professor of neurosurgery, psychiatry, and biobehavioral sciences at UCLA’s David Geffen School of Medicine, said in a press release. “It has both scientific value in terms of understanding how memory works in humans and using that knowledge to really boost memory.”

These results were published Thursday in the journal Nature Neuroscience.

Enhancing a memory circuit

As you can probably imagine, it’s not easy to study the brain head-on without peeling away layers of skin, muscle, and bone. Certain patient populations, like those with epilepsy, make the endeavor a bit easier since they more often undergo surgical procedures to determine the parts of the brain responsible for their seizures, which may include implanting electrodes to directly capture abnormal brain activity.

A patient with epilepsy being outfitted with non-invasive electrodes for an EEG to measure brain activity.

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For their study, Fried and his colleagues rounded up 18 people between the ages of 19 and 47 with drug-resistant epilepsy (meaning that typical medications used for treatment failed to stop their seizures) and intracranial electrodes implanted into their frontal lobes (part of the neocortex). The participants spent two days in a sleep lab where before nodding off, they were tasked with learning and remembering 25 paired images of recognizable famous people, like Marilyn Monroe and Mahatma Gandhi, and animals like a cat or a bird (the pairs were presented as “pet owners” and their pets). A set of new paired images, also 25 in total, were shown the subsequent night.

While sleeping, the participants either got deep-brain stimulation (the second night) or none (the first or control night). The deep-brain stimulation happened in a specific way the researchers call a real-time closed-loop system. Basically, the system, consisting of electrodes tracking shifts in brain waves and activity, listened for when the brain fell into the state of deep sleep associated with memory consolidation. When it did, the system then delivered the pulses of electricity through the participants’ electrodes, prompting neurons in the front lobe and any regions they connected with to fire in sync like members of a marching band stepping in time.

In the morning, the participants were tested on their memory for the associations, as well as their ability to recognize "lure" images similar to the learned associations but differing in some ways. The rule of thumb being the better their memory, the more successful the participants would be at distinguishing the learned images from the misleading lure ones.

Fried and his colleagues believed that by synchronizing the deep-brain stimulation with the natural electrical rhythms of the hippocampus during sleep, they could boost memory processing. And it did: Compared to the night when they didn’t get any stimulation, the participants practically aced their memory tests.

From what the researchers could tell, it all boiled down to deep-brain stimulation enhancing the electrochemical dialogue between the hippocampus and the neocortex. The improved interaction wasn’t only limited to these two regions but also multiple neocortical areas, even in the opposite hemisphere of the brain.

“We found we basically enhanced this highway by which information flows to more permanent storage places in the brain,” said Fried.

Deep brain stimulation for everyone?

Rafael Pelayo, clinical professor at Stanford University’s Sleep Medicine Division, says these findings unveil a bit of the iceberg underwater that is memory consolidation, emphasizing once again how crucial sleep is to human health.

“Sleeping is the best bang for your buck if you want to enhance your thinking, enhance your memory,” Pelayo tells Inverse. “I think this is the bigger point of this [study]. It’s just more evidence that sleep is key to memory formation.”

During dementia, including Alzheimer's disease, the ability to form, retain, and retrieve memories is significantly impaired. The specific impact on memories can vary depending on the stage and type of dementia, as well as the areas of the brain affected.

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But these findings also highlight, Pelayo says, the opportunity of using deep-brain stimulation to maybe get even more bang for our cognitive buck, especially in treating neurodegenerative conditions like Alzheimer’s disease and other forms of dementia. What we could potentially have in the future, says Pelayo, are transcranial devices worn while asleep delivering just the right amount of brain stimulation according to our particular cognitive needs.

“For Alzheimer’s right now, none of the medications [on the market] have great effects yet,” says Pelayo. “So, could we whip the brain into shape by improving this issue? The idea of targeting specific parts of the brain externally with deep-brain stimulation may make a lot of sense.”

Other research efforts exploring the use of deep-brain stimulation are so far promising. One 2022 study out of Boston University found that externally stimulating the brain with small doses of electrical current helped older adults with their short-term memory for up to a month, according to CNN. Another 2023 study published in the journal Cell Stem Cell looked into non-invasive deep-brain stimulation and Alzheimer’s disease in mice and found it stimulated the growth of new neurons as well as turned on biochemical pathways that cleared away plaques associated with the disease.

More research needs to be done until we can find a clear-cut way to zap our brains smarter and better. Until then, go get some quality shuteye.

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