I read a few pages of a book or a few words before going to bed, and when I wake up, I find that I am actually very impressed. Have you had this similar experience?
Scientists have always wanted to study this phenomenon, but it has been limited by technical conditions to collect weak neural activity signals in the human brain at night. With the recent development of wireless data transmission technology in brain-computer interface, the opportunity has finally come.
In experiments involving volunteer testers, researchers have for the first time obtained direct evidence that the motor cortex of the human brain “replays” daytime activity during sleep.
The first author of the paper, Daniel Rubin of Harvard Medical School, said:
What we found was incredible, he (the test subject) basically practiced all night automatically while sleeping.
Related papers have been published in The Journal of Neuroscience, a well-known journal in the field of neuroscience.
Your brain learns faster while you sleep
The subject, codenamed T11, was unfortunately quadriplegic due to spinal cord injury. He implanted the BrainGate project team’s invasive brain-computer interface electrodes, the same set of devices used by T5 testers who participated in the mind-typing study last year.
In this experiment, T11 needs to play a simple video game during the day:
First observe the order in which the colored areas light up, and then move the cursors in sequence according to the recall.
This is a classic task in brain-computer interface research, where the pattern of neural activity is easier to capture and identify, and it has also appeared in related studies many times before.
For 10 consecutive days, T11 needs to do training at 13:45-16:00 in the afternoon, and sleep at 23:00 in the evening until 9:00 in the next morning.
During training, the brain-computer interface can decode and record the neural activity of his brain’s motor cortex in real time.
T11 was not informed of the specific content of the experiment, only to do recovery training as usual, and fall asleep as usual at night.
But during those 10 days, the researchers compared the data recorded by the brain-computer interface while he slept with the data during the day.
After processing the data with means such as Kalman filtering, it was found that nighttime neurons replayed daytime training at higher frequency intervals than expected.
The firing patterns of neurons during T11 sleep were highly consistent with those during daytime training, and on a few occasions they even matched exactly.
The phenomenon, called offline replay, has been previously demonstrated in mice and humans during daytime breaks. This is the first time that replays during human sleep have been observed. And the data shows that the speed of replay at night is 1-4 times faster than that during the day. That is to say, when you are asleep, your brain is not only automatically learning what it learned during the day, but also accelerating it.
And you are completely unaware of this.
The harder the task, the more active the brain
A series of previous studies have also verified that neural activity in the hippocampus and neocortex during sleep in mice can practice maze walking.
And the similar offline replay phenomenon when humans rest during the day, etc.
Combining these findings with experimental results, the researchers came up with a view:
Replay learning may be a retention mechanism across multiple brain regions, including semantic, navigational, and motor control systems. and further support the role of sleep in memory consolidation.
In addition to this, the study also validated several important previous findings:
First, the replay occurs mainly in biological slow-wave sleep (Slow-wave Sleep), more commonly known as the non-rapid eye movement stage (Non-REM Stage), or deep sleep.
Second, replay activity was highly correlated with hippocampal-induced Sharp Wave Ripple.
Sharp ripples are rapid bursts of synchronized neuronal activity that create a high-frequency oscillation.
Third, the harder the task was practiced during the day, the more intense the replayed activity at bedtime.
In future plans, the BrainGate consortium research team intends to systematically change the difficulty of the task and conduct more in-depth research.
The BrainGate Consortium, initiated by clinicians, neuroscientists, and institutions such as Brown University, Harvard Medical School, and Massachusetts General Hospital, aims to use brain-computer interface technology to describe patients who have lost mobility due to neurological disease or injury.
One More Thing
Since the brain is consolidating memory during deep sleep, what is the brain doing during the REM period (that is, the stage where you have the most dreams)?
A previous Science paper explained this.
During REM, MCH neurons in the hippocampus responsible for secreting melanin-clustering hormone help the brain to actively forget unimportant information. Since dreaming mainly occurs during the rapid eye movement period, MCH neurons are active at this time, which is one of the reasons why the content of the dream is forgotten after waking up. So, have you ever woken up and remembered everything you read the day before?
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