One of the dominant scientific theories as to how the brain converts new information into long-term memories while sleeping is during a type of overnight dialogue that takes place between the hippocampus and the cerebral cortex which take place during a phase of deep sleep in which brain waves are very slow and neurons across brain regions alternate between rapidly firing in both syn and silence.
Their findings were reached by using a novel “closed loop” system that delivers electrical pulses to one brain region that is precisely synchronized to brain activity recorded from another region. The researchers report that targeted deep brain stimulation during a key time during the sleep cycle appears to improve memory consolidation, and they believe that this study offers insights into how deep brain stimulation while sleeping may assist those living with memory disorders such as Alzheimer’s disease in the future.
The memory sleep theory was tested through the use of electrodes in the brains of 18 epilepsy patients at UCLA Health, the electrodes were previously implanted to help identify the source of their seizures during a hospital say that typically lasts around one and a half weeks. This project was conducted over 2 days, in which the participants viewed photo pairings of animals and 25 easily identifiable celebrities before bedtime. After the viewing participants were tested on their capacity to remember the parings, and aging the following morning after a night of undisturbed sleep.
On the second night, the participants viewed 25 new pairings before going to sleep, but this time they also received targeted electrical stimulation overnight before they were retested for memory recall in the morning. To deliver the electrical stimulation a real-time closed-loop system was created that listens to the brain’s electrical signals and when the patient falls into a deep period of sleep associated with memory consolidation the system delivers gentle electric pulses instructing the rapid firing of neurons to play in sync.
The researchers reported that each participant performed better on the memory testing after receiving electrical stimulation during a night of sleep in comparison to sleep without stimulation. Additionally, key electrophysiological markers also indicate that information was flowing between the cortex and the hippocampus providing physical evidence supporting the memory consolidation theory.
“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,” says study co-author Itzhak Fried, the 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 has both scientific value in terms of understanding how memory works in humans and using that knowledge to really boost memory.”
“We found we basically enhanced this highway by which information flows to more permanent storage places in the brain,” Prof. Fried adds.
Professor Fried previously demonstrated that electrical stimulation can strengthen memory for the first time in 2012, which was published in the New England Journal of Medicine. Since that publication, he has continued to investigate how deep brain stimulation may help to improve memory, and he has recently received a $7 million grant from the NIH to explore if artificial intelligence could help to locate and strengthen specific memories in the brain.
“In our new study, we showed we can enhance memory in general,” Prof. Fried concludes. “Our next challenge is whether we have the ability to modulate specific memories.”
