For the first time, scientists can see how the brain records our memories when we sleep

But the exact way in which the brain stores our memories is poorly understood.

Now for the first time, tiny microelectrodes implanted in the brains of two people with epilepsy show how brain neurons light up during sleep to “replay” our short-term memories to transfer them to more permanent storage. That research published Tuesday in the journal Cell Reports.

“This research is very interesting,” Dr. Richard Isaacson, who heads the Alzheimer’s Prevention Clinic at Weill Cornell Medicine and the New York Presbyterian Hospital.

“Apart from decades of research, it is still somewhat unclear how ‘short term’ memories are stored as ‘long term’ memories that can be recalled later,” said Isaacson, who was not involved in the study.

“Using a brain-computer interface is an interesting way to study memory because it can record patterns of brain cell activity and then look for the right patterns later,” he added.

Track individual neurons

The study was conducted at PT BrainGate, an academic research consortium consisting of Brown University, Stanford University and Case Western Reserve University.

Braingate has spent dozens or more years developing brain-computer interfaces that allow people with amyotrophic lateral sclerosis (ALS) and other neurological diseases, brain injury or loss of limbs to be able to use their brain signals to move computer cursors, robot arms and other assistive devices. to communicate and control his world.

“Neurons are small. They are about 10 microns in size,” said computer neurologist and study author Blata Jarosiewicz. “And the macro electrodes that are approved for human use, such as electrodes that stimulate the deep brain, are too large to record the individual surge activity of each neuron.”

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But in Braingate, surgeons implanted a series of minute electrodes into the brains of two people with sensory and motor paralysis, allowing people to “think” about moving their hands in a direction. By mapping the way neurons behave during thinking, the decoder can translate thoughts into speech or act through artificial fake limbs and robotic assistive devices.

“Different neurons have different direction of choice,” said Jarosiewicz, who was assistant research professor at BrainGate at the time of the study.

“Some increase their shooting rates each time people want to move their hands up; others when people want to move right or left,” he said. “And we can tell from the activation patterns in all the neurons in which direction that person wants to move their hands.”

Play Simon Says

In the study, two people with implantable devices were asked to take a nap where their neuronal activity was recorded as a baseline. Then each of them plays sequential games that are modeled after the 1980 electronic hit game Simon, where the player is asked to repeat the same sequence of light movements as the game has just been displayed.

Instead of moving their arms to follow Simon, of course, the two people used their minds to repeat the game while their neural activity was recorded. Finally, both of them were asked to rest and take a nap.

The results showed that during take that nap neuron activity is identical to that recorded while two subjects actually play the game. This means their brain continues to play Simon after they sleep, repeating the same pattern in their brain at the neuron level.

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“Understanding fully how memory is stored in the brain can help unlock the secrets to optimal cognitive function,” said Isaacson, who is the trustee of the McKnight Brain Research Foundation, which funds research in new treatments and prevention of neurological diseases.

The use of this technology to study brain movements during sleep is why “this study is unprecedented,” Jarosiewicz said. “There aren’t many scenarios where someone will have a multi-electrode array placed in their brain, where the electrodes are small enough to be able to detect the firing activity of individual neurons.”

The procedure is clearly rare. In fact, Braingate only planted 12 such devices in the consortium’s work history, Jarosiewicz said.

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“This supports the idea that to optimize memory and learning functions, people need to prioritize calming activities – most importantly enough sleep – to keep our ‘machines’ working at peak performance,” Isaacson said.

There are several monitoring devices at home, Isaacson said, such as straps and rings worn on the wrist, which claim to be able to track the various stages of sleep that are perhaps the most important for memory consolidation.

Hopefully, he said, “future studies will help clarify certain stages of sleep – deep sleep, REM sleep – where repeat memory occurs most often.”