It’s been known before that Sudoku number puzzles improve memory and crosswords vocabulary but the researchers showed that any mental exercise really do limber up the brain and make it more quick-witted.

It has also been thought the only way to improve problem-solving ability was by practicing the specific problem-solving task you wanted to get better at. However, this theory has proven wrong. A study led by a Swiss-American team showed that general problem solving ability could be improved by carrying out unrelated mental exercises and puzzles.
In their experiment, the researchers gave 35 volunteers a series of mental training exercises that were previously designed to improve their working memory and they also had 35 more subjects who were a control group.
The exercises included seeing a sequence of squares appearing one after another on the computer screen every three seconds and then having to decide whether a certain square was at the same position as another one previously seen in the sequence. Simultaneously, They were listening to spoken letters and had to decide whether the currently heard letter was the same as one presented two or three steps earlier in the sequence. If they did well the task became harder, while if they did badly it became easier. The exercises were repeated for between 8 and 19 days. In the end, the researchers assessed their problem-solving ability and compared it to the group who had not taken part in the exercises.

The study results showed that the group who took part in the puzzles had a significantly improved problem solving ability. The study also showed that the more they trained, the more problems they could solve.
However, positive results stayed out where there was no motivation.

This is the first evidence that mental exercises improve intelligence and problem-solving ability. The researchers reported that time spent on crosswords, Sudoko and other number and word games was a high-quality time.