According to Japanese scientists, the best way to train the brain is the mental calculation. The mental calculation is based on actively involving working memory, and working memory is a type of memory that stores information in the mind while we are working with it. It is often short-lived, but some theorists agree that they still differ from each other. Working memory can be used to manipulate stored information, while short-term memory only provides short-term data storage.
It is also possible to train working memory when counting quickly in reverse order, for example, from 100 to 1. However, psychologists recommend a different task – the reverse count minus 3: 400, 397, 394, etc. On the other hand, for example, this exercise: come up with a word for all the letters of the alphabet. It is good because it allows you to resume access to half-forgotten words in memory and use those connections of nerve cells that would have been dormant. It is like in a game where you have to come up with a word that starts with the last letter of the word spoken by another player.