The researchers call this type of stimulation “synchronization.” They also tested another form of stimulation, known as “mixed phase,” in which the electrode delivered pulses to the frontal lobe without regard for hippocampal activity.
To see if these types of stimuli affect memory, the scientists used an experiment in which patients were presented with pictures of famous people, paired with pictures of celebrities. pet. Each patient then spent one night in which stimulation was given while they were asleep and one night without any intervention. In the mornings after each night, the patients were shown photos of celebrities they had interacted with the night before, as well as “seduce” images of people they had never met before. The team assessed whether the patient could recognize the celebrity, could match the person with the relevant pet, and could reject attractive images.
The researchers found that after the stimulus was synchronized, the ability to recognize previously learned celebrities was better than it was overnight with no intervention. This improvement was not seen in patients exposed to mixed phase stimulation, suggesting that the timing of stimulation is critical for memory enhancement.
“The most interesting part that we didn’t anticipate is that we saw the possibility of elimination,” said Maya Geva-Sagiv, a former postdoctoral fellow in Fried’s lab and study co-author. correctly discard those misrepresented images that have increased. This means that after synchronous stimulation during a good night’s sleep, patients are not attracted to attractive images. Overall, these results indicate an increase in memory accuracy after synchronized stimulation.
This increase in memory accuracy is also reflected in the physiology of the brain. The team found that synchronized stimulation causes an increase in sleep spindles—bursts of neural activity (which, unsurprisingly, look like spindles on an EEG. ) is known to play a role in memory consolidation. According to Geva-Sagiv, the patients with the greatest improvement in memory accuracy also had the greatest increase in sleep spindles. The team also found that after the stimulus was synchronized, the brain coordinated better—hippocampal ripples occurred in tandem with the slow waves and spindles during sleep.
Nir draws an analogy with two children on a swing: the hippocampus on one swing and the neocortex on the other. “All we did was look at one of the swings, and based on its movement, timed some very subtle thrusts to the other swing to get them in sync,” he says. . “Really, the way I think about it is that we’re providing a bit of a headwind—we’re helping the sleeping brain do what it’s doing more efficiently anyway.”
Michael Zugaro, a neuroscientist at the Center for Interdisciplinary Research in Biology at the College de France who was not involved in the study, has previously seen improvement in memory consolidation following an associated form of synchronous stimulation in rats. “It is interesting to see that the general principles that we can find in different species also apply to humans,” he said.
For Buzsaki, more research is needed to see if this process of memory consolidation is similar in healthy people and if the same improvement in memory accuracy can be achieved. The question, he said, is whether the quality of improvement is due to standardizing on something that is “already perfect in your brain but not so perfect in an epileptic patient” or is it something that can be optimized. optimization in everyone. However, both he and Zugaro note that implanting electrodes into the human brain is an invasive procedure that raises serious ethical concerns when performed without a clear clinical need.
Despite that, Fried hopes that these results can help patients with different types of memory disorders. In the future, he wants to develop the technique as a method to amplify certain types of memories and possibly even get rid of bad ones—which could be useful for things like PTSD. For Geva-Sagiv, the ability to stimulate further advances for patients made publishing the study, which had been in the works for a long time, worthwhile. “I am delighted that we can now add more knowledge to this very important area,” she said.
