It turns out that if you stimulate your brain while sleeping at night you will get better memory

While sleeping at night, the work of fixing the short-term memory information stored in the hippocampus in the human brain to the temporal lobe as a long-term memory is carried out. Recent studies on the mechanism of this memory have revealed that memory stimulation can be enhanced by strengthening the mechanism of memory retention by adding electrical stimulation to the brain when sleeping.

Closed-loop slow-wave tACS improves sleep dependent long-term memory generalization by modulating endogenous oscillations | Journal of Neuroscience
http://www.jneurosci.org/content/early/2018/07/23/JNEUROSCI.0273-18.2018

Overnight brain stimulation improves memory: Non-invasive technique enhances memory storage without disturbing sleep - ScienceDaily
https://www.sciencedaily.com/releases/2018/07/180723142907.htm

This study was conducted by research teams such as Nicholas Ketz and Praveen Pilly of the University of New Mexico. Research has been conducted with funds provided by the US Department of Defense, and research is being conducted on memory improvement in groups of both healthy people and those suffering from diseases.

As mentioned above, in the human brain, long-term memory is created by transferring information to the temporal lobe. When transferring short-term memory accumulated in the hippocampus to the temporal lobe, brain waves with a very slow cycle are produced in the brain, but electric stimulation that exactly matches this electroencephalogram is externally applied to the brain The research team revealed that it is possible to enhance the memory function by giving it.

In the experiment, we first gave the subject a task of finding objects that could pose a threat to ourselves, such as "explosives" and "sniper soldiers". Next, the subjects had sleeping overnight, at that time the subjects were divided into two groups, one group did not have anything attached, the other group had the outside of the head I went to bed while wearing a device for giving electrical stimulation.

The stimulator is based on "noninvasive brain stimulation technique" which can stimulate the brain without stabbing the needle etc in the head. The research team used this device to stimulate an electrical signal with a very slow period of 0.5 to 1.2 cycles (0.5 to 1.2 Hz) per second. At this time, the electric signal is added to the brain with the frequency and phase matching perfectly with the actual brain wave.

Subjects were given tasks similar to the previous day on the day after having made the two groups sleep in this way. The contents of the task is "to find dangerous goods" like the previous day, but the situation given at that time is different from the previous day. After having both tasks executed, it turned out that the group receiving electrical stimulation while sleeping left good results for the other groups. In other words, the memory of the previous day remained stronger in the brain of the group who received electrical stimulation, and based on that memory, we were able to make a decision to protect ourselves from danger.

The research team thinks that this technology shows that it is possible to improve memory without disturbing sleep. It is expected that people who are suffering from memories of daily life, as well as restoring the memory power of those whose brain functions are partly declining due to some kind of disability.