I try to go out on my bike when I and the weather feel up to it , although I did take a bike out for a play in the snow earlier this year. Cycling may have improved my fitness a bit but it has also helped mentally in giving me something to think about . Chatting on here , trying to solve people's questions, and even trying to solve my own can be stimulating.
The feeling you get from having fixed something, filed and polished some scratches out a pair of handlebars or brake levers to successfully rebuilding a wheel can help to improve your mental fitness, or may help prevent a decline .