Ask the Brains; August/September 2007; Scientific American Mind; by Mark A. W. Andrews, Barry L. Beyerstein; 1 Page(s)

Thought-stimulating activities such as Sudoku and crossword puzzles elicit positive emotional reactions from many (if not most) people. Science has not yet found a definitive answer as to why we enjoy these games so much, but research into emotions, though in an early state, has yielded some clues.

In your question you hint at a distinction between pleasure and satisfaction. In fact, MRI brain scans have provided evidence that there is indeed a significant difference between these feelings. Pleasure and happiness are passive emotions that happen to us as the result of outside stimuli. Satisfaction, on the other hand, involves an active pursuit--it is the emotional reward we get after adapting to a new situation or solving a novel problem. Studies have found that novelty is important in evoking satisfaction, which helps to explain why, even though all Sudoku puzzles are similar, solving each one of them instills a sense of accomplishment.