Deep-Brain Stimulation for Memory Improvement During Sleep

The primary idea of how human memory is strengthened when we sleep has also been supported by the first direct data reported by researchers. Although it is well recognized that sleep is essential for improving memory, researchers are still striving to understand exactly how this process occurs in the brain at night.

The leading scientific theory of how the brain consolidates memories during sleep is supported by new study from Tel Aviv University and the University of California, Los Angeles (UCLA) Health. This research was conducted on human subjects. The study team also discovered that focused deep brain stimulation during a crucial phase of sleep appeared to enhance memory consolidation.

The study, which was co-authored by Itzhak Fried, MD, PhD, and was published on June 1 in the journal Nature Neuroscience, may provide fresh information about how deep-brain stimulation during sleep may one day benefit patients with memory problems like Alzheimer's disease. An innovative "closed-loop" technique that accurately matched electrical pulses in one brain region to brain activity recorded from another region was used to achieve this.

The cerebral cortex, which is linked to higher brain functions like reasoning and planning, and the hippocampus, the brain's memory hub, communicate throughout the night, according to the leading explanation for how the brain converts new information into long-term memories while you sleep. When brain waves are particularly sluggish and neurons in various brain regions alternate between quickly firing in sync and silence, this happens during a stage of profound sleep.

"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," said Fried, director of epilepsy surgery at UCLA Health and professor of neurosurgery, psychiatry, and biobehavioral sciences at the David Geffen School of Medicine at UCLA. It is valuable from a scientific standpoint to comprehend how human memory functions and to apply that information to significantly improve memory.

The brains of 18 epilepsy patients at UCLA Health provided a unique opportunity for the researchers to test this idea of memory consolidation using electrodes. The electrodes were inserted into the patient’s brains to assist in determining the cause of their seizures throughout hospital stays, which normally last 10 days. The investigation took place over two mornings and nights. Before going to bed, study participants were shown photographs of 25 famous people, including instantly recognizable figures like Marilyn Monroe and Jack Nicholson. They were tested right away to see if they could remember which celebrity was associated with which animal, and they were checked once more the next morning following a sound sleep.

On another occasion, they watched 25 brand-new celebrity and animal pairs before turning them in. This time, they underwent focused electrical stimulation overnight, and the next morning, their capacity to remember the pairings was evaluated. Fried compared the real-time closed-loop system the researchers developed to this musical conductor in order to offer this electrical stimulation: When patients entered the deep slumber associated with memory consolidation, the system "listened" to the brain's electrical impulses and gave gentle electrical pulses instructing the rapidly firing neurons to "play" in sync.

Following a night of sleep with the electrical stimulation as opposed to a night of undisturbed sleep, each subject examined performed better on memory tests. Important electrophysiological indicators also showed that information was moving between the hippocampus and the whole cortex, offering concrete proof that memory consolidation was taking place.

Fried remarked, "We discovered we essentially improved this highway by which information flows to more long-term storage places in the brain."

In 2012, Fried published a paper in the New England Journal of Medicine that demonstrated for the first time how electrical stimulation might increase memory. Since then, Fried's research has continued to examine how deep brain stimulation may enhance memory and is currently focusing on the crucial sleep stage. To investigate whether artificial intelligence can support the identification and reinforcement of certain memories in the brain, he just won a $7 million NIH grant.

Fried stated, "In our recent work, we have shown that we can improve memory generally. "Whether we have the ability to modulate particular memories is our next challenge."

Reference: “Deep brain stimulation during sleep enhances human brain synchrony and memory” 1 June 2023, Nature Neuroscience.

DOI: 10.1038/s41593-023-01342-3