It is widely assumed that people need to engage in intellectual activities such as solving crossword puzzles or mathematics problems in order to maintain mental sharpness as they age. In fact, however, simply talking to other people--that is, participating in social interaction, which engages many mental and perceptual skills--suffices. Evidence to this effect comes from a study showing that the more social contact people report, the better their mental skills.
Many medical conditions and treatments that adversely affect a person's mental sharpness also tend to increase that person's social isolation most seriously weakens the force of the evidence cited.